ClarkVision.com

To Clarkvision.com Galleries

Digital Camera Sensor Performance Summary

http://www.clarkvision.com/imagedetail/digital.sensor.performance.summary

R. N. Clark Email contact (is encoded to prevent spam):
has the following form: username@qwest.net where
username is rnclark

All images, text and data on this site are copyrighted.
They may not be used except by written permission from Roger N. Clark.
All rights reserved.



Contents

Data on this page are from the references below and from the Digital Camera Sensor Analysis pages on this site: http://www.clarkvision.com/imagedetail/index.html#sensor_analysis



Introduction

Modern digital cameras contain electronic sensors that have predictable properties. Foremost among those properties is their relatively high Quantum Efficiency, or ability to absorb photons and generate electrons. Second is that the electronics are so good in most cameras, that noise is as low as 3 or 4 electrons and rarely worse than about 15 electrons from the sensor read amplifier. With the low noise and high Quantum Efficiency, along with the general properties of how the sensors collect the electrons generated from photons, it is possible to make general predictions about camera performance. An important concept emerges from these predictions that we are reaching fundamental physical limits concerning dynamic range and noise performance of cameras. See References 18, 20 (from electronic sensor companies) and Reference 24 (from University class lecture notes) for more details about the above well-established concepts and how electronic sensors operate.

The ideal sensor absorbs every photon, each photon would generate an electron and every electron would be collected and counted to form the image, all done with no added noise. Would images from such a camera be perfect (no noise and infinite dynamic range)? NO! All measurements of light (photons) still have inherent noise, called photon noise. The dynamic range is not infinite, but would have a maximum of the number of photons collected. For example, if you collected 1,000 photons, the dynamic range would be 1000:1 or almost 10 photographic stops.

Dynamic range is defined in this document and elsewhere on this site as:

where the full well capacity in electrons represents the number of photons detected (see Reference 20). In the perfect sensor (previous paragraph), the read noise would be zero, but the minimum signal is 1 photon and the noise would be square root 1 = 1 photon, giving the dynamic range of 1000. In real digital cameras, amplifier and analog-to-digital converter noise contributes to the read noise, so each ISO has a different measured read noise, resulting in changes in the dynamic range with different ISOs. This article will present data and models of the read noise, full well capacity, and dynamic range.

In the physics of photon counting, the noise in the signal is equal to the square root of the number of photons counted because photon arrival times are random. The reason for this dependence is Poisson Statistics (Wikipedia has an excellent article on Poisson statistics). For example Table 1 shows the signal-to-noise ratio when detecting different numbers of photons.

Table 1a
Photons Noise Signal-to-noise
Ratio
9 3 3
100 10 10
900 30 30
10000 100 100
40000 200 200
90000 300 300

Why is this important? It turns out that the noise making up the majority of images we view from good modern digital cameras is dominated by photon counting statistics, not other sources. So to make an image with a high signal-to-noise ratio, one must collect the most photons possible. Modern electronic sensors have a method for collecting the electrons from photons and storing them in the sensor until the electrons are transferred from the chip to the electronics in the camera where the signal is amplified, digitized and converted into an array of numbers to be recorded in a memory card and later displayed as an image by a computer.

Both CCD and CMOS silicon sensors used in today's digital cameras exploit a property of semiconductors. Silicon is a semoconductor. When a photon is incident on the silicon, the photon may be absorbed, and the energy from the photon excites an electron, moving it into what is called the "conduction band" from the low energy state called the "valence band." There is an energy gap, called the "band gap" across which the electron must move. The band gap sets the lower limit (longest wavelength) of the photon energy that can be absorbed by the electron to move it into the conduction band (see Reference 24 for more details). For silicon, that wavelength is about 11,000 angstroms (1.1 microns) in the infrared. Photons with wavelengths shorter than this value have higher energies, and those energies include wavelengths visible to our eyes, called the visible spectrum. Once an electron is excited unto the conduction band, the challenge is to capture it before it moves far (like electrons flowing great distances in a copper wire, where electrons are flowing in the conduction band).

The electric field in the silicon is modified by adding impurities (called doping, e.g. parts per million of arsenic or boron or other elements in the columns in the periodic table on each side of silicon) to control were the electrons flow. Voltages are applied to the silicon, and when a photon is absorbed, primarily by the electrons in the valence band, the electrons will excited into the conduction band and flow toward positive voltage. These electrons are also called "photoelectrons." The local electric fields produced by the doping and applied voltages trap the electrons in small regions (pixels in imaging sensors). The trapped electrons correspond to absorbed photons, and in the sensor industry, photons and electrons are interchanged in describing sensor performance.

Thus, when a digital camera reads 10,000 electrons, it corresponds to absorbing 10,000 photons. So the graphs shown in this article that are in units of electrons, like Sensor Full Capacity, also indicate how many photons the sensor pixel captured. The camera electronics also generates a small amount of noise, and from a measurement perspective, that noise is in electrons and the noise source, whether camera electronics or from photon noise, gets mixed into the images you observe. With measurement techniques, the various noise sources can be isolated and their individual contributions measured. This article summarizes available data for numerous sensors, both digital cameras and from sensor manufacturer data sheets.

Fundamental factors set sensor performance of semiconductors like CMOS and CCDs. These include the absorption length in silicon, the efficiency of photon absorption (which is very high, typically 40-50% for modern digital cameras), and electron charge density in the silicon. Blue wavelength photons have shorter absorption lengths in silicon than red or green photons. Major factors in limiting the maximum number electrons captured in a semiconductor image sensor are the absorption length and electron densities. The wavelength-variable absorption lengths in silicon are exploited in the development of the Foveon sensor and some Sigma digital cameras, for example, allowing a single spatial pixel to separate red green and blue colors. Unfortunately, the absorption lengths overlap too much for fine wavelength discrimination. Table 1b shows the absorption lengths.

Table 1b
Absorption in Silicon
Wavelength
(angstroms)
Wavelength
(microns)
Color Absorption
(1/e) Length
in Silicon
(microns)
4000 0.40 ~violet 0.19
4500 0.40 ~blue 1.0
5000 0.50 ~blue-green 2.3
5500 0.55 ~green-yellow 3.3
6000 0.60 ~orange 5.0
6500 0.65 ~red 7.6
7000 0.70 ~red limit 8.5
Data from Reference 25.

The absorption lengths of photons in Table 1B are the 1/e depth (e = 2.7183), or the 63% probability of absorption length. Some photons can, in reality travel several times this distance before being absorbed. These absorption lengths impact performance as pixels become smaller. For example, small sensor digital cameras currently have pixels smaller than 2-microns. What happens when red photons enter the silicon and after 5 microns only 63% of them are absorbed, and after 10 microns (10 pixels) 13% are still moving through the silicon being absorbed at greater distances from the original pixel? If the absorbed photon results in an electron in the conduction band, it likely contributes to photons several pixels away from the target pixel.

What follows are sensor performance data. For each property, note the trends. See the section on the Sensor Performance Model. for details of the model.

Full Well Capacity

The property that describes the capacity to hold the electrons in each pixel that are generated from photons is called the "Full Well Capacity." As a pixel holds more electrons, the charge density increases. There are finite upper limits to the charge density of electron storage, and undesirable side effects can occur, including charge leaking into adjacent pixels, called blooming (e.g. see reference 19). Blooming was common in early CCDs causing streaks from brigh objects in the image.

Full well capacities of some cameras and sensors are shown in Figure 1. Because of the finite and fixed absorption lengths of photons in silicon (Table 1b), the full well capacities are basically a function of pixel area (and not volume).


Figure 1. Digital camera and sensor Full Well Capacities are shown. Digital camera data are shown as brown diamonds, and sensor data from manufacturer's data sheets are shown in blue squares. Data values are from Table 2. Note the Canon 20D and 30D use the same sensor. Details of the model are given below, see Sensor Performance Model. The model uses an electron density of 1700 electrons/square micron (the higher the electron density, the greater the problem with side effects, including blooming).


Signal-to-Noise Ratio

Full well capacity is important for maximum signal-to-noise ratio and dynamic range. Figure 2 shows the signal-to-noise ratio at ISO 100 on an 18% gray card. Eighteen percent is close to the average scene intensity in regular photographs, so Figure 2 shows the typical signal-to-noise ratio in a typical photograph. Dynamic range is shown in Figure 4, and shows a small trend with pixel size.

Full well capacity does not necessarily indicate low light performance even though more electrons (electrons excited and collected by the absorption of photons) means better low light performance. For example, the Nikon D50 plots low in Figure 1. But that full well occurs at ISO 200 where most other cameras are at ISO 50 to 100. Thus, the Nikon D50 is actually more sensitive, and this is indicated on the Unity Gain ISO data discussed below and presented in Figure 6 (where the Nikon D50 plots very high). Low light performance is controlled by the Quantum Efficiency of the device combined with the total photons the device collects.


Figure 2. The signal-to-noise ratio of an 18% gray card assuming the camera meter would place 100% reflectance at the saturation level of the sensor at ISO 100 (in practice many cameras are close to this exposure level). Note the D50 has a minimum ISO of 200, so the signal-to-noise ratio is for ISO 200, and plots square root 2 lower (for a ISO 200 signal-to-noise ratio plot, the D50 would appear relatively higher). There is a clear trend of increasing signal-to-noise ratio with increasing pixel size. Data from Table 2. Details of the model are given below, see Sensor Performance Model.

Read Noise

For detecting the lowest signals, read noise is a controlling factor. Read noise is expressed in electrons, and represents a noise floor for low signal detection. For example, if read noise was 10 electrons, and you had only one photon converted in a pixel during an exposure, the signal would mostly be lost in the read noise. (It is possible to see an image where the signal is 1/10 the read noise; see: Night and Low Light Photography with Digital Cameras http://www.clarkvision.com/photoinfo/night.and.low.light.photography.) Older CCDs tend to have read noise levels in the 15 to 20 or more electrons. Newer CCDs in better cameras tend to run in the 6 to 8 electron range, and some are as low as 3 to 4 electrons. The best CMOS sensors currently have read noise in the 3 to 4 electron range. Figure 3 shows read noise for various cameras and commercially available sensors. One can see that there is no real trend with pixel pitch.

Read noise dominates the signal-to-noise ratio of the lowest signals for short exposures of less than a few seconds to a minute or so. For longer exposures, thermal noise usually becomes a factor. Thermal noise increases with temperature, as well as exposure time. Thermal noise results from noise in dark current, and the noise value is the square root of the number of dark-current generated electrons. Thermal noise will be discussed in more detail in the future on this web page when more dark current data becomes available.


Figure 3. Read noise for various sensors. Data from Table 2. Note older cameras (e.g. Canon 10D, S60) have higher read noise than newer models. Currently Canon's technology leads in read noise performance. Lower read noise values = better performance. Nikon currently clips the average read noise at zero, losing some data. Canon includes an offset, so processing by some raw converters can preserve the low end noise, which can be important for averaging multiple frames to detect very low intensity subjects (as in astrophotography).

Dynamic Range

A large dynamic range is important in photography for many situations. The pixel size in digital cameras also affects dynamic range. Dynamic range is defined here to be the maximum signal divided by the noise floor at each ISO. The noise floor is a combination of the sensor read noise, analog-to-digital conversion limitations, and amplifier noise. These three parameters can not be separated when evaluating digital cameras, and is generally called the read noise. The measured read noise near unity gain is essentially equal to sensor manufacturer's published specifications for read noise, so the zero signal case is read noise limited. As you might have surmised by now, with the larger pixels collecting more photons, those larger pixels also have a higher dynamic range. Figure 4 shows the maximum dynamic range possible from each sensor, based on full-well capacity / best read noise, assuming no limitation from A/D converters. Figure 5 shows the measured dynamic range from 3 cameras with significantly different pixel sizes as a function of ISO. The full sensor analyses for these 3 cameras (as well as other cameras) can be found at: http://www.clarkvision.com/imagedetail/index.html#sensor_analysis. One sees that actual dynamic range of a digital camera decreases with increasing ISO as long as the range is not limited by the A/D converter. At higher ISOs, it is obvious that large pixel cameras have significantly better dynamic range than small pixel cameras, but at low ISO there is not much difference. If 14-bit or higher analog-to-digital converters were used, with correspondingly lower noise amplifiers, the dynamic range could increase by about 2 stops on the larger pixel cameras. The smallest pixel cameras do not collect enough photons to benefit from higher bit converters.


Figure 4. Dynamic range of sensors. Many sensors are limited to just under 12 photographic stops by the camera's 12-bit analog-to-digital (A/D) converter. The 14-bit A/D limit is difficult to achieve in the high speed, low power applications of a digital camera, thus current 14-bit cameras are only slightly improving over 12-bit systems; see Figure Figures 5 and 8 for more information. Look for future DSLRs to use 14 or 16 bit A/Ds. The film dynamic range is for similar spatial resolution as the digital sensors and applies to slide film; print film does slightly better, but is not up to the large pixel digital cameras. Sensor data is from Table 2. Details of the model are given below, see Sensor Performance Model. Ultimately, with zero electronics noise, dynamic range would be limited by the number of photons collected, thus would still show a dependence on pixel size.


Figure 5. The measured dynamic range for 4 different cameras is shown. Large pixel cameras have a larger dynamic range. The small pixel camera has a very good dynamic range, but that range rapidly deteriorates with increasing ISO. The large pixel cameras produced up to 2007 were limited by 12-bit analog-to-digital converters at low ISOs. The lower noise, 14-bit Canon 1D Mark III has boosted performance beyond the slightly larger pixel 1D Mark II. High ISO performance is about 1/2 stop better, similar to what was claimed by Canon when the camera was announced. This improvement is due to a better fill factor and lower read noise. Without the low noise 14-bit converter, the Mark III would plot to the lower left of the Mark II. The flattening of the dynamic range toward lower ISOs is due to noise in the camera electronics, such as the A/D converter (See Figure 8 for models of noise sources).

Unity Gain

A concept important to the fundamental sensitivity of a sensor is the Quantum Efficiency. But in terms of camera performance other factors also play a role, including the size of a pixel, and the transmission of the filters over the sensor (the Bayer RGBG filter, the IR blocking filter, and the blur filter). Larger pixels collect more light, just like a large bucket collects more rain drops in a rain storm. A parameter that combines the quantum efficiency and the total converted photons in a pixel, which factors in the size of the pixel and the transmission of the filters (the Bayer RGBG filter, blur filter, IR blocking filter), is called the "Unity Gain ISO." The Unity Gain ISO is the ISO of the camera where the A/D converter digitizes 1 electron to 1 data number (DN) in the digital image. Further, to scale all cameras to equivalent Unity Gain ISO, a 12-bit converter is assumed. Since 1 electron (1 converted photon) is the smallest quantum that makes sense to digitize, there is little point in increasing ISO above the Unity Gain ISO (small gains may be realized due to quantization effects, but as ISO is increased, dynamic range decreases). Figure 6 shows the Unity Gain ISO for various cameras and sensors that can be purchased from manufacturers. It is clear that there is a trend in ISO performance as a function of pixel size. Gains for various cameras are shown in Table 3 as a function of ISO. Note in practice for 14-bit systems lower ISO may be employed if the A/D converter does not limit performance. In comparing actual performance of 14-bit A/D converters (e.g. see Figure 8a) and the read noise in Table 4, the lowest read noise performance remains the same (~ISO 1600) for both 12-bit DSLRs and 14-bit DSLRs. Thus the Unity Gain ISO values in Figures 6a and 6b apply equally well for all cameras currently tested to set optimum performance in low light. In practice, set the gain at the nearest 2x ISO (e.g. ISO 400, 800, 1600, 3200), as the data obtained at other ISOs are often simply multiplied by the camera's digital processor. In many cases, it is usually difficult to see the performance difference between ISO 800 and 1600 except for the lower dynamic range decrease at the higher ISO.


Figure 6a. Unity gain is shown as a function of pixel pitch. Digital cameras are shown in brown diamond symbols, and values computed from sensor manufacturer data sheets are shown in blue squares. The lowest value of ISO 100, at pitch 2.3 microns, is for the Canon S70 P&S camera, while the highest digital camera value, at ISO 1600, is for the Canon 5D with 8.2 micron pixels. This indicates that the Canon 5D collects about 16 times the number of photons as a Canon S70 small pixel camera, given the same f/ratio and exposure time. However, ISO depends on the camera manufacturer's choice of amplifier gain, thus Unity Gain ISO is only a guide. For example, the Canon 5D and 1D Mark II collect similar numbers of photons with the same pixel size, but have different Unity Gain ISOs. The Nikon D3, with an 8.46-micron pixel pitch plots off the top of the chart; see Figure 6b. See Figures 1, 2, and 7 for other indicators of light collection performance. Data from Table 2.


Figure 6b. Unity gain is shown as a function of pixel pitch. Same data as in Figure 6a, with expanded scale.

Low Light Sensitivity Factor

Unity Gain ISO describes the high signal part of an image (the highlights) at high ISO, and read noise the performance corresponding to the low signal end of the photograph. But if a camera was delivering more photons to a pixel, then read noise alone does not give a complete story of the performance in the shadows. The "Low-Light Sensitivity Factor" describes the high iso shadow performance (Figure 7). It also describes the low light performance in shadows of exposures up to tens of seconds at high ISO. In astrophotography, a high Low-Light Sensitivity Factor would record the most faint stars, at least for exposures where thermal noise did not dominate.


Figure 7 The Low-Light Sensitivity Factor describes the camera performance in shadows or darkest parts of an image at high ISO. Low-Light Sensitivity Factor = Unity Gain ISO divided by read noise in electrons. A higher value shows better performance in recording shadow detail at high ISO. Derived from data in Table 2.

Noise Sources

At high signal levels (most of the range of a digital camera image), noise is dominated by photon noise, the inherent random arrival times of photons at the sensor. At the lowest signal levels, other sources contribute. There is sometimes confusion over what are the sources of such low level noise. For example, Table 4 below shows apparent read noise is high (when expressed in electrons) at low ISO and decreases with increasing ISO. Figures 8a and 8b show the sources and reasons for these trends. At low ISO large pixel cameras, typical of DSLRs collect enough photons that photon noise is small compared to read noise and noise from the analog-to-digital converter (ADC). Some call this quantization noise, and while such noise contributes to the total ADC noise, other noise sources in the ADC stage dominate, especially on newer cameras with 14-bit ADCs (the Canon 40D in Figure 8a). On small pixel cameras, the analog gain is high enough that at low signals, read noise dominates the noise sources and ADC noise is a small factor (Figure 8b). The small pixel camera in Figure 8b looks like is has better low ISO performance than the large pixel cameras in Figure 8a, but that is not the case, because the large pixel cameras collect many times more photons/pixel in a given exposure. The true low signal performance in these cases is illustrated in Figure 7.


Figure 8a Noise sources of total apparent read noise for 2 cameras: the 12-bit ADC in the 1D Mark II shows the ADC noise limits performance at low ISO, while sensor read noise dominates at high ISO. The 14-bit Canon 40D has an ADC stage with relatively low performance, and thus the camera is still limited by ADC noise at low ISO and does not achieve 4x improvement over the 12-bit system. A 4x improvement is not expected based on typical ADC performance; see reference 15 and examine 12 and 14-bit ADC specifications for devices running in the many megahertz range. The data indicates, however, that better ADCs could improve the low ISO performance (including dynamic range), and we see this in the Canon 1D Mark III (as indicated by a slight improvement in Figure 5: the smaller pixels of the Canon 1D Mark III plot at a similar performance level as the larger pixel Canon 1D Mark II). From reference 15, 16-bit ADCs appear to be needed, as only such high performance devices have the signal-to-noise ratios needed for these sensors.


Figure 8b Small pixel cameras have analog gain stages with high gain such that the 12-bit ADC is not a limiting factor. See Figure 7 for effective low signal performance. Even though the sensor is read noise limited at low signals, the small pixels collect many fewer photons in a given exposure compared to large pixel cameras.

Apparent Image Quality (AIQ)

Apparent image quality is a subjective measure, that includes resolution and signal-to-noise ratio. While it is not a new concept, I present my own working definition:

AIQ = StoN18 * MPix / 20.0 = sqrt(0.18*Full well electrons) * Mpix / 20.0,

where StoN18 is the signal-to-noise delivered by the sensor on an 18% gray target, assuming a 100% reflective target just saturates the sensor, and Mpix is the number of megapixels. StoN18 is computed from pixel performance before Bayer de-mosaicking: indicative of the true performance of each pixel. Table 2 shows calculated AIQ. Actual image quality depends on the lens delivering a certain resolution, so use these values as a rough guide of what might be possible. More information on AIQ and comparison to film can be found at: http://www.clarkvision.com/imagedetail/film.vs.digital.summary1.html.


Figure 9 Apparent Image Quality. The models use the same equation and parameters as the model in Figure 4. The model closely predicts performance for all modern cameras (within about 10% for large pixels, and 20% for small pixels). Older cameras and sensors fall below the model, e.g. typically due to low fill factors. Higher quantum efficiency (QE) sensors than the model (45%) would plot above the model (by a factor of square root 2, 1.41x higher AIQ for a ~100% QE sensor). Solid colored lines indicate constant sensor size in megapixels. Dashed colored lines indicate constant format sized sensors. The "Full-Frame" sensor is the same size as 35-mm film. As one moves to the left along a constant format line, AIQ first increases until diffraction begins to take effect, then AIQ decreases. Diffraction at f/8 is used for the Full Frane, 1.3x-crop, and 1.6x-crop sensors, and f/7 for the 4/3 sensor (long dashed lines), f/4 for the Full Frame and 2/3" small-format sensor, and f/2.8 for the smallest sensor shown, 1/1.8" (short dashed lines). The smaller f/ratios are needed as sensor size decreases in order to make the model fit observed data. This indicates smaller format cameras must have very high quality lenses in order to deliver performance at high megapixels. Diffraction limits the effective megapixels. When pixels become very small, they hold so few electrons that dynamic range suffers, and this causes the turn down in AIQ at pixel sizes below 2 microns pixel pitch.

The data for AIQ for some sensors in Figure 9 plot below the model curves. This is best seen in the trend below the 1.6x-crop model. Those points represent older cameras that had lower efficiency (e.g. the Canon 10D, plotting at 7.4 micron pixel pitch), probably due to lower fill factors, lower quality microlenses, and lower quantum efficiencies. The newer cameras plot close to the model lines. The Nikon D3 plots below the model because of the reported low full-well capacity (more data at ISO 100 are needed to confirm the D3 full-well capacity).

The AIQ model and sensor data in Figure 9 is for the lowest ISO filling the pixel with electrons. AIQ for higher ISOs drops approximately with the square root of the ISO, so quadruple the ISO and the AIQ drops by 2x. If new sensors came out with higher quantum efficiency (about a 2x improvement is possible), the AIQ would be increases by the square root of the increase, so a 1.4x improvement is possible.

Sensor Performance Model

The sensor models in Figures 1, 2, 4, 6, 7, and 9 is simple but accurately describes many sensors. Note the greater the distance in data points from the model generally occurs for older sensors. e.g. probably due to lower fill factors, lower quality microlenses, and lower quantum efficiencies. Newer sensors tend to plot closer to the model.

The model assumes a quantum efficiency similar to current digital camera sensors (~45%), a full well capacity = 1,700 electrons per active square micron (the electron density), read noise = 4 electrons (except in Figure 4 a model with read noise =2 electrons is also shown), and a 1-micron dead space between pixels. would have an active area of 9 square microns collecting 9*1,700 = 15,300 electrons. For the small format sensors, the dead space was decreased to 1/2 micron only in Figure 9, AIQ. AIQ is limited in the model by 2 factors: 1) diffraction, and 2) lower dynamic range as pixel size decreases. The model limits resolution (effective megapixels) to the Modulation Transfer Function at 50% response (MTF50). MTF50 occurs at f-ratio / 1.56 microns/pixel. For example, at f/8 the MTF50 occurs at 5.13 microns, so pixels smaller than about 5 microns will be limited in spatial resolution with a diffraction limited f/8 lens. AIQ is decreased linearly in the model when dynamic range (defined as full well divided by read noise) falls below 10 photographic stops. This breakpoint is seen in the constant-format curves (dashed lines) below 2-microns in Figure 9.



Data Tables

Below are tables that give other derived parameters for many cameras along with data from the manufacturer's data sheets for their sensors. Methods for determining gain, full-well capacity, and read noise can be found at references 1-5. Specific procedures are described in Procedures for Evaluating Digital Camera Sensor Noise, Dynamic Range, and Full Well Capacities; Canon 1D Mark II Analysis http://www.clarkvision.com/imagedetail/evaluation-1d2.

The noise model for digital cameras is:

N = (P + r2 + t2)1/2, (eqn 1)

Where N = total noise in electrons, P = number of photons, r = read noise in electrons, and t = thermal noise in electrons. Noise from a stream of photons, the light we all see and image with our cameras, is the square root of the number of photons, so that is why the P in equation 2 is not squared (sqrt(P)2 = P). The signal corresponding to equation 1 would simply be the number of photons, P, so the signal-to-noise ratio, SNR, in a pixel is:

SNR = P/N = P/(P + r2 + t2)1/2. (eqn 2)

It is this predictable signal and noise model that allows us to predict the performance of digital cameras. It also shows us that those waiting for the small pixel camera to improve and equal the performance of today's large pixel DSLR will have a long wait: it simply can not happen because of the laws of physics. So, if you need high ISO and/or low light performance, the only solution is a camera with large pixels. Related to this topic, see also: The f/ratio Myth and Digital Cameras http://www.clarkvision.com/photoinfo/f-ratio_myth, and The Depth-of-Field Myth and Digital Cameras http://www.clarkvision.com/photoinfo/dof_myth.

Table 2
Digital Camera Sensor Performance Data

                        Sensor           Appar-    Sensor Dynamic       
                    --------------------   ent         Range                 12-bit
                    full   Read  Thermal Image    (full well/         Pixel   Unity 
Camera or    Type   well   Noise  Noise  Qual-        read noise)    Spacing  Gain  Mega-       Sensor size
Sensor               (electrons) e-/sec  ity  QE  linear*   stops   (microns) ISO*  Pixel   pixels         mm       reference
                                (@ ~10C) AIQ  %
--------------------------------------------------------------------------------------------------------------------------------
KAF-4320     CCD  550,000   22     7      68  65  25000     14.6     24.0    10070  4.3 2084 x 2084   50.02x50.03   K4320
KAF-1301E    CCD  220,000   15            13  65  15600     13.8     16.0     4030  1.3 1280 x 1024   22.0 x 17.1   K1301
Nikon D2Hs                                                            9.4           4.0 2464 x 1632   23.1 x 15.1
KAF-18000CE  CCD  100,000   18           121  39   5560     12.4      9.0     1830 18.0 4904 x 3678   46.05x 35.0   K1800
KAI-11002    CCD   60,000   30            56  37   2000     11.0      9.0     1465 10.8 4008 x 2672   37.25x 25.70  K11002
Sigma SD10                                                            9.0           3.5 2304 x 1536   20.7 x 13.8
Nikon D3     CMOS  65,600    4.9          69      13400     13.7      8.46         12.1 4256 x 2832   36.0 x 23.9
Canon 5D     CMOS ~80,000e   3.7          76     ~20000e   ~14.3e     8.2     1600 12.7 4368 x 2912   35.8 x 23.9   13
Canon 1DMII  CMOS  79,900*   3.9          49  38  20500     14.3      8.2     1300  8.2 3504 x 2336   28.7 x 19.1    3
Nikon D70    CCD   24,500    6.3          20       3890     11.9      7.9     1070  6.0 3008 x 2000   23.7 x 15.6    10
Nikon D50    CCD   30,500    7.5          22       4060     12.0      7.9     1488  6.0 3008 x 2000   23.7 x 15.6    3
Nikon D40    CCD                                                      7.9           6.0 3008 x 2000   23.7 x 15.6
Pentax*istDs CCD                                                      7.8           6.0 3008 x 2008   23.5 x 15.7
KAI-16000    CCD   30,000   16            59  45   1875     10.9      7.4      730 16.1 4904 x 3280   36.1 x 24.0   KAI16000
Canon 10D    CMOS  44,200   10            28  26   4420     12.1      7.4     1120  6.3 3072 x 2048   22.7 x 15.1   10
Canon 300D   CMOS  45,500   10            29       4550     12.1      7.4     1110  6.3 3072 x 2048   22.7 x 15.1   1
Canon 1DsMII CMOS                                                     7.2          16.6 4992 x 3328   36   x 24
Canon 1DMIII CMOS  70,200    4.0          57      17500     14.1      7.2     1000 10.1 3888 x 2592   28.1 x 18.7
Leica M8     CCD                                                      6.85         10.3 3936 x 2630   27   x 18
KAF-10500    CCD   60,000   15            56  40   4000     12.0      6.8     1465 10.8 4010 x 2686   27.0 x 18.0   K10500
KAF-31600    CCD   60,000   16           167       3750     11.9      6.8     1465 32.1 6536 x 4912   46.05x 35.0   KAF31600
Sony IMX021  CMOS                                                     6.5          12.5 4320 x 2888   28.0 x 22.3   
Canon 1DsIII CMOS                                                     6.4          21.1 5616 x 3744   36.0 x 24.0
Canon 30D    CMOS  51,400    3.6          39      14270     13.8      6.4     1200  8.2 3504 x 2336   22.5 x 15.0   10
Canon 20D    CMOS  51,400    3.6          39      14270     13.8      6.4     1200  8.2 3504 x 2336   22.5 x 15.0   10
Canon 20Da   CMOS  51,400    3            39      17130     14.1      6.4     1200  8.2 3504 x 2336   22.5 x 15.0
Canon 350D   CMOS  43,000    3.7          35      11600     13.5      6.4     1040  8.0 3456 x 2304   22.2 x 14.8
Nikon D200   CCD   32,680    7.4          38       4416     12.1      6.1      800 10.0 3872 x 2592   23.6 x 15.8    3
Nikon D80    CCD                                                      6.1          10.2 3872 x 2592   23.6 x 15.8
Sony A100    CCD                                                      6.1          10.2 3872 x 2592   23.6 x 15.8
Pentax K10D  CCD                                                      6.07         10.2 3872 x 2592   23.5 x 15.7
Olympus E330 NMOS                                                     5.74          7.5 3136 x 2352   18.0 x 13.5
Canon 400D   CMOS                                                     5.7          10.1 3888 x 2592   22.2 x 14.8
Canon 40D    CMOS  43,400    4.2          45      10300     13.3      5.7     1300 10.1 3888 x 2592   22.2 x 14.8 
Nikon D300   CMOS  42,000    4.6          53       9130     13.1      5.5     1000 12.3 4288 x 2848   23.6 x 15.8   17
Nikon D2X    CCD                                                      5.5          12.2 4288 x 2848   23.7 x 15.7
KAF-8300     CCD   25,500   16            29  40   1594     10.6      5.4      623  8.6 3326 x 2504   19.7 x 15.04  K8300
Olympus E300 CCD                                                      5.3           8.0 3264 x 2448   17.3 x 13.0
KAI-10100    CCD   25,000   10            36  45   2500     11.3      4.75     610 10.8 3676 x 2856   17.86x 13.49  KAI10100
Olympus E410 MOS                                                      4.7          10.0 3648 x 2736   17.3 x 13.0
Olympus E3   MOS                                                      4.7          10.0 3648 x 2736   17.3 x 13.0
Sony ICX205  CCD   10,000                                             4.65          1.4 1360 x 1024    7.6 x  6.2   ICX205
YM-3170A     CMOS  35,000   20    <2      13       1750     10.8      3.3      427  3.2 2056 x 1544   6.40 x 4.80   4
Canon S60    CCD   22,000   13.6          16       1616     10.7      2.8      268  5.0 2592 x 1944   7.18 x 5.32
MT9D131      CMOS  17,000    3.6              37   4700     12.2      2.8      207  1.9 1600 x 1200   4.63 x 3.52    MT9D131
Fuji F30     CCD                                                      2.67          6.3 2848 x 2136   7.60 x 5.70 
Nikon 8800   CCD                                                      2.7           8.0 3264 x 2448   8.80 x 6.60
Canon S70    CCD    8,200    3.2          14       2562     11.3      2.3      103  7.1 3072 x 2304   7.18 x 5.32   3
Panasonic
   Lumix LX2 CCD                                                      2.1          10.2 4224 x 2376   8.9  x 5.0
Canon S3 IS  CCD                                                      2.0           6.0 2816 x 2112   5.76 x 4.29
Canon G7     CCD                                                      1.97         10.0 3648 x 2736   7.18 x 5.32 
Casio
    EX-Z1000 CCD                                                      1.97         10.0 3648 x 2736   7.18 x 5.32 
Panasonic
  Lumix FZ50 CCD                                                      1.97         10.0 3648 x 2736   7.18 x 5.32 
Samsung NV10 CCD                                                      1.97         10.0 3648 x 2736   7.18 x 5.32 (Sony CCD)
Canon SD950  CCD                                                      1.9          12.1 4000 x 3000   7.60 x 5.70
Sony H5      CCD                                                      1.87          7.2 3072 x 2304   5.76 x 4.29
Sony ICX629  CCD                                                      1.86          7.2 3112 x 2328   5.76 x 4.29 ICX629
Sony W300    CCD                                                      1.80         13.4 4224 x 3168   7.60 x 5.70
Sony DSC-H7  CCD                                                      1.76          8.1 3264 x 2448   5.76 x 4.29
Panasonic
      FZ18   CCD                                                      1.76          8.1 3264 x 2448   5.76 x 4.29
Notes:
AIQ = StoN18 * MPix / 20.0 = sqrt(0.18*Full well electrons) * Mpix / 20.0, where StoN18 is the signal-to-noise of the sensor on an 18% gray target, assuming a 100% reflective target just saturates the sensor, and Mpix is the number of megapixels.
full well iso is the lowest iso where the camera reaches full well (=100 for DSLRs and 50 for the S60 and S70 point and shoot cameras). Example, the Canon 1D Mark II at iso 800 has a gain of 1.6, so: 1.6 * 4095 * 800/100 ~ 52400.
*At ISO 100, the Canon 1D MII records a maximum of 52,300 electrons; at ISO 50, 79,900 electrons are recorded, but that occurs about 3/4 of the 12-bit linear scale, at 3071 on the 12-bit DN range.
An "e" following a value means estimate.
The Kodak KAF-18000CE is targeted as a medium format sensor; see reference 12.
Possible dynamic range of the sensor is theoretical and in practice is often limited by the 12-bit (or 10-bit) analog to digital converters in many cameras.
Sensor sizes from manufacturer's data sheets or product reviews.

Some additional parameters, grouped by camera for easier comparison are shown below.

Table 3a Camera Gain in 12-bits
                                     Gain (electrons / 12-bit DN)
        -----------------------------------------------------------------------------------
         Canon  Canon Canon Canon Canon Canon  Canon Canon Nikon Nikon Nikon  Canon Canon
         1DMII   5D    20D   10D   350d  300D   40D*  400D D200  D70   D50    S60   S70
-------------------------------------------------------------------------------------------
ISO  50   26.03 32.6                                                          5.4   2.06
ISO 100:  13.02 16.3  12.4  11.4  10.2   11.1  12.5  11.0  7.98               2.7   1.03
ISO 200:   6.51  8.2   6.2   5.5   5.1    5.6   6.2   5.48 4.0   6.0   7.45   1.3   0.51
ISO 400:   3.25  4.08  3.1   2.7   2.56   2.78  3.1   2.74 2.0   2.98  3.72   0.7   0.26
ISO 800:   1.63  2.0   1.5   1.4   1.3    1.4   1.6   1.37 1.0   1.34  1.86
ISO1600:   0.81  1.0   0.8   0.7   0.6    0.7   0.78  0.68 0.5         0.93
ISO3200:   0.41  0.5   0.4

* = 14-bit system. Canon 1D Mark II values from reference 3. Canon 1DMII are newer values determined Feb 12, 2006 with firmware 1.2.4, reference 3.
Canon 10D values from Tam Kam-Fai posted on digital_astro@yahoogroups.com, 20D, 300D, D70 ISO 400 values from Terry Lovejoy, reference 1. Canon S60 5-megapixel point and shoot digital camera from this study.
The 5D, 350D ISO 400 values are from reference 13. Reference 21 derives similar gains for the Canon 5D. The 20D value also agrees with reference 13 where 3.09 electrons/DN is reported. Reference 13 reports the 10D at ISO 400 has a gain of 2.34 electrons/DN, 15% lower than used here. 40D and 400D data from References 14.

Table 3b Camera Gain in 14-bit Systems
                                     Gain (electrons / 14-bit DN)    
        ----------------------------------------------------------------------------------- 
         Canon   Canon   Nikon   Nikon
         1DMIII   40D     D3     D300
------------------------------------------------------------------------------------------- 
ISO  50   4.8 
ISO 100   4.8     3.40            2.74
ISO 200   2.4     1.70    4.1     1.37
ISO 400   1.2     0.85    2.1     0.67
ISO 800   0.60    0.42    1.1     0.32
ISO1600   0.30    0.21    0.5     0.16
ISO3200   0.15            0.25    0.082
Notes:
Canon 1D Mark III and 40D are from Clarkvision analyses. Note the 1D Mark III does not change gain between ISO 50 and 100. ISO 50 photos will be saturated a stop lower.
Canon 1DMIII saturates at 70500 electrons at DN 15280 out of 16383, ISO 50 (1360 electrons/square micron).
Canon 40D saturates at 43400 electrons at DN 13824 out of 16383, ISO 100 (1336 electrons/square micron).
Nikon D3 info derived from references 16 and 21; Reference 21 derives a saturated full well capacity of 65,568 electrons. This is in contrast to the stated (December 2007) 340,000 electrons in reference 16 (which is several times the full well capacity on a per square micron basis that any other CMOS or CCD sensor). For example, 340,000 gives 4761 electrons per square micron much higher than any published value I have seen. I will use ~137,000 electrons as the full well, which gives 1918 electrons / sq. micron, still a value that is probably too high.
Nikon D300 data derived from reference 17; Reference 17 states the camera saturates at 12-bit DN 3830. The full well capacity should be about: 2.74 * 16383 * 3830/4095 ~ 42,000 electrons.

Table 4a Read Noise
                             Read Noise (electrons)
        ----------------------------------------------------------------------------------
         Canon  Canon Canon Canon Canon Canon  Canon Canon Nikon Nikon Nikon  Canon Canon
         1DMII   5D    20D   10D   350d  300D   40D*  400D D200  D70   D50    S60   S70
------------------------------------------------------------------------------------------
ISO  50:  30.6  59.7                                                          13.6  4.1
ISO 100:  16.6  30.1  25.3  15.9   21.6        17.9        10.0                     3.4
ISO 200:   8.95 15.6  13.5  11.0   11.5         9.9         8.1       13.4          3.2
ISO 400:   5.56  8.4   7.5  10.6    7.2         6.5   7.0   7.7   6.3               4.3
ISO 800:   4.04  5.2   4.8   9.0    4.9    10   5.2         7.4  13    7.47
ISO1600:   3.90  3.7   3.6   9.0    3.7         4.3         7.4
ISO3200:   3.93  3.7

* = 14-bit system. Full well depth (electrons for max DN at iso 100) (maybe we should call this the "camera maximum DN well depth", because it is not necessarily the real full well depth). Canon 1D Mark II values from reference 3. Canon 1DMII values determined Feb 12, 2006 with firmware 1.2.4.
Canon 10D values from Tam Kam-Fai posted on digital_astro@yahoogroups.com, 20D, 300D, D70 values from Terry Lovejoy, reference 1, and http://www.astrosurf.org/buil/20d/20dvs10d.htm The Canon 5D, 350D, and 20D values computed from the gains above and read noise in DNs from Table 3 of Reference 13. 40D and 400D data from References 14. For comparison, reference 21 derives for the Canon 5D, read noise = 32.7 electrons at ISO 100; 15.5 at ISO 200, 8.9 at ISO 400, and 3.8 at ISO 1600.

Table 4b Additional Analyses
                             Read Noise (electrons)
        ----------------------------------------------------------------------------------- 
         Canon   Canon  Nikon   Nikon 
         1DMIII   40D    D3     D300
------------------------------------------------------------------------------------------- 
ISO  50   24.4
ISO 100   24.4   20.1
ISO 200   12.2          17.6     6.6
ISO 400    7.4    6.6    9.7     5.9
ISO 800    5.1                   5.1
ISO1600    4.2    4.2    4.9     4.6
ISO3200    4.0                   4.7
ISO6400    4.1 
Notes:
Canon 1D Mark III data from Jerry L., analyzed here by Clark.
Canon 40D analyzed here by Clark. Nikon D3 info derived from references 16 and 21. Nikon D300 data derived from reference 17.

Table 5
                                  ISO 100
               Maximum    Possible Signal-to-noise Pixel
Camera          Signal     Maximum    18% Gray    Spacing         Sensor size
             (electrons)                card     (microns)    pixels           mm
---DSLRs ---
Canon 1DMII    52,300        229         97         8.2    3504 x 2336     28.7 x 19.1
Canon 10D      44,200        210         89         7.4    3072 x 2048     22.7 x 15.1
Canon 300D     45,500        213         90         7.4    3072 x 2048     22.7 x 15.1
Nikon D70      48,800        221         94         7.9    3008 x 2000     23.7 x 15.6
Canon 20D      51,400        227         96         6.4    3504 x 2336     22.5 x 15.0
---P&S ----
Canon S60*     22,000        105         44         2.8    2592 x 1944     7.18 x 5.32
Nikon 8800                                          2.7    3264 x 2448     8.80 x 6.60
Canon S70                                           2.3    3072 x 2304     7.18 x 5.32
Panasonic
  Lumix FZ20                                        2.2    2560 x 1920     5.76 x 4.29
Signal-to-noise assumes photon noise limited. Read noise, and other factors can only degrade this number (read noise is insignificant for the maximum possible and 18% gray card signal-to-noise ratios for the cases shown here). * The Canon S60 full well is for ISO 50. P&S means point and shoot. The Canon 20D full well and signal-to-noise is conditional on an initial number that may have a large error bar.

References

1) http://www.pbase.com/terrylovejoy/dslr_tech

2) http://www.axres.com/technote1.html.

3) http://www.clarkvision.com/imagedetail/index.html#sensor_analysis.

4) http://www.dpreview.com/news/0009/00090603ymedia3mpcmos.asp

5) CCD Chip Data Tables

6) http://www.microscopedealer.com/products/photosystems/nikon_dxm1200f.htm

7) Example data sheet: Kodak KAF - 0261E 512(H) x 512(V) Pixel Full-Frame CCD Image Sensor Performance Specification http://www.datasheetcache.com/Kodak/KAF0261E%20Rev.%20%20D%20Preliminary.pdf

8) CCD Gain. http://spiff.rit.edu/classes/phys559/lectures/gain/gain.html

9) Charge coupled CMOS and hybrid detector arrays http://huhepl.harvard.edu/~LSST/general/Janesick_paper_2003.pdf

10) Canon EOS 20D vs Canon EOS 10D and Canon 10D / Canon 20D / Nikon D70 / Audine comparison http://www.astrosurf.org/buil/20d/20dvs10d.htm

11) http://www.photomet.com/library_enc_fwcapacity.shtml

12) The Kodak KAF-18000CE Image Sensor 4904 (H) x 3678 (V) Full-Frame CCD Color Image Sensor http://www.kodak.com/global/plugins/acrobat/en/digital/ccd/products/fullframe/KAF-18000LongSpec.pdf

13) Evaluation du Canon EOS 5D, pour les applications astronomiques http://www.astrosurf.com/buil/5d/test.htm

14) Faint Light Application of Canon EOS 40D http://astrosurf.com/buil/eos40d/test.htm

15) Analog Devices A/D Converter Specifications http://www.analog.com/IST/SelectionTable/?selection_table_id=124

16) Comparison Elements Between Nikon D3/D300 and Canon 40D for Faint Light Applications http://astrosurf.com/buil/nikon_test/test.htm

17) A comparison of the Nikon D300 and Canon 40D sensors by Emil Martinec, 2007, http://theory.uchicago.edu/~ejm/pix/20d/posts/tests/D300_40D_tests

18) Optical Measurement Technique GmbH (includes sensor data).

19) Concepts in Digital Imaging Technology CCD Saturation and Blooming

20) Concepts in Digital Imaging Technology CCD Noise Sources and Signal-to-Noise Ratio http://learn.hamamatsu.com/articles/ccdsnr.html

21) Technical comparison of Nikon D3 and Canon EOS 5D camera characteristics, by Peter Facey, http://www.brisk.org.uk/photog/d35dcomp.html

22) Concepts in Digital Imaging Technology Dynamic Range http://learn.hamamatsu.com/articles/dynamicrange.html

23) Optimum Scaling Buried-Channel CCD's, Chatterjee, P.K.; Taylor, G.W. Electron Devices, IEEE Transactions on Volume 27, Issue 3, Mar 1980 Page(s): 553 - 562

24) ASTR 511 (O'Connell) Lecture Notes, CCD'S IN ASTRONOMY, University of Virginia, 2007. http://www.astro.virginia.edu/class/oconnell/astr511/lec11-f03.html

25) Concepts in Digital Imaging Technology, Quantum Efficiency http://learn.hamamatsu.com/articles/quantumefficiency.html

K1301) Summary Specification, Kodak KAF-1301E Image Sensor. www.kodak.com, February 5, 2003, Revision 3.

K4320) Summary Specification, Kodak KAF-4320E, April 19, 2004, Revision 1.0.

8300) Summary Specification, Kodak KAF-8300CE Image Sensor. www.kodak.com, Revision 1.1.

10500) Summary Specification, Kodak KAF-10500 Image Sensor. www.kodak.com, Revision 3.0 MTD/PS-0962, September 26, 2006.

K11002) Summary Specification, Kodak KAI-11002 Image Sensor. www.kodak.com, Interline CCD, Revision 1.0 MTD/PS-0938, January 30, 2006.

K1800) Summary Specification, Kodak KAF-1800CE Image Sensor. www.kodak.com, May 16, 2005, Revision 4.

KODAK) Kodak Full-Frame CCD Products (Full Frame means the full chip is used, not full 35mm frame).

KAI10100) Kodak MAI-10100 Image Sensor, 10.8 mpixels.

KAI16000) Kodak KAI-16000 Image Sensor, 16.1 mpixels.

KAF316000) Kodak KAF-31600 Image Sensor, 32.1 mpixels, 2006, revision 2.

SONY) SONY CCD Image Sensors.

ICX205) Sony ICX205 4.65 micron pixel CCD; data table and link to pdf at www.ccd.com.

ICX629) ICX629 Sensor: High-Resolution Diagonal 7.208 mm (Type 1/2.5) 7.24M-Effective Pixel Digital Still Camera CCDs for Consumer Products Support VGA Resolution Moving Picture Imaging.

ICX476) ICX476 Sensor: High-Resolution Diagonal 9.102 mm (Type 1/1.8) 8.13M-Effective Pixel Digital Still Camera CCD for Consumer Products

Hamamatsu) Hamamatsu Solid State Division CCD sensor specifications.

MT9D131) Micron MT9D131 1/3.2 inch CMOS Image Sensor.


Notes

DN is "Data Number." That is the number in the file for each pixel. I'm quoting the luminance level.

16-bit signed integer: -32768 to +32767

16-bit unsigned integer: 0 to 65535

Photoshop uses signed integers, but the 16-bit tiff is unsigned integer (correctly read by ImagesPlus).


Home Page: ClarkVision.com

Back to: Digital Camera Sensor Analysis pages on this site: http://www.clarkvision.com/imagedetail/index.html#sensor_analysis

Back to: Digital Imaging Information index on this site: http://www.clarkvision.com/imagedetail

First published November 16, 2006.
Last updated February 23, 2008