Photographic Noise Performance Measures Based on RAW Files Analysis of Consumer Cameras
Abstract
:1. Introduction
2. Theoretical Background
2.1. Noise in CMOS Image Sensors
- The read noise is decomposed in two independent components: pre and post amplifier noises. For low ISOs, the post amplifier term is the dominant one and for large ISOs the input read noise is the most important. The gain of the amplifier is related to the ISO dial in the camera: double the ISO, double the gain G. The RAW domain values in DU can be input-referred to the domain dividing by the gain factor, e.g., . Since these two components are independent, the read noise is:
- In modern cameras, the ADC noise has been reduced so much that not only for high ISOs, but even at base ISO (typically ISO 100). It means that the read noise can be simplified to only the input read noise . Since signal is also amplified by the same factor G, the output remains approximately constant for all ISOs. As a consequence, the sensor that shows this behavior is named ISO-invariant.
- The read noise drops at a certain ISO. To achieve this, a single amplifier model is not enough; since the output noise is , it must at least double when ISO is doubled. The way to model this behavior is by using a two stage amplification, where first is a low noise amplifier. From base ISO to the ISO where the sensor changes from a low to high gain mode, the read noise increases with ISO. At that ISO it drops and above that ISO it grows again. These sensors are called dual gain sensors and they allow to increase the dynamic range at high ISOs as we will analyze later. The read noise model for a dual sensor is:
2.2. Signal to Noise Ratio, Exposure and ISO
- Even for poor noise performance sensors (large read noise), if exposure can be set so that light arriving to the pixel corresponding to the darkest area of the scene is high enough to guarantee that the photon noise is dominant, the is as good as the one you would get with an ideal perfect sensor, since , independent of the sensor. The limit on increasing the exposure is given by the full well capacity (when the sensor saturates and highlights are burnt). The higher is the full well capacity of the pixel, the better, since the greater is the before saturation.
- In the deepest shadows (small signal values S), the key factor is the read noise. The smaller is the read noise, the better.
- If you increase exposure, the grows more quickly in the shadows than in the highlights. Doubling the exposure doubles the in the shadows where the read noise dominates and improves the in the highlights by a factor of . Therefore, in situations of very low exposure, such as night photography, each additional captured photon is priceless.
- Increasing exposure is not the same as increasing “exposure”. For photon noise to be dominant, it must be satisfied that or its equivalent in electrons . If you raise the ISO (greater G), it increases , but the read noise also grows with G. The best way to ensure that photon noise is much larger than read noise is by doing s very large, that is, G small for the same value of S. Thus, the condition must be understood as: the exposure s should be as large as possible.
- If the extra photon is captured because the aperture size is increased (lower f-stop), the depth of field is reduced; if you are photographing a landscape you do not want a shallow depth of field.
- If extra light is achieved because the exposure time is increased, there is a risk of trepidation (photography with no tripod) or missing the moment (fast action photography).
- If exposure time is so long that the sensor heats up too much, dark current noise begins to be a major problem.
2.3. Dynamic Range
2.4. Photographic Noise Performance Measurements
2.4.1. Same Format but Different Resolution Sensors
2.4.2. Any Format and Resolution Sensor
3. Materials and Methods
3.1. Description and Source of Material
3.2. Experiment: Canon 50D Noise Model at ISO 100
4. Results
4.1. Canon 50D Analysis
4.1.1. Canon 50D: Signal to Noise Ratio Curves
4.1.2. Canon 50D: , Exposure and ISO
4.1.3. Canon 50D: Read Noise Model and Exposure
4.2. and ISO for Dual Gain ISO Invariant Sensors
4.3. Comparative Performance Evaluation
4.3.1. Pixel Curves
4.3.2. Pixel Dynamic Range
4.3.3. Photo Level Results
5. Discussion and Conclusions: How to Expose in Digital Photography
Funding
Acknowledgments
Conflicts of Interest
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Camera | Dimensions | Mp | Pixel Size | k |
---|---|---|---|---|
Canon 50D | 15.1 | 4.7 | 2.23 | |
Canon 5DMIII | 22.3 | 6.3 | 4.83 | |
Canon M10 | 18 | 4.3 | 2.17 | |
Canon 80D | 24 | 3.7 | 2.03 | |
Canon 5DMIV | 30.1 | 5.4 | 4.00 | |
Nikon D5100 | 16.2 | 4.8 | 2.29 | |
Nikon D750 | 24 | 6 | 4.69 | |
Nikon D5500 | 24.2 | 3.9 | 1.97 | |
Nikon D7200 | 24 | 3.9 | 2.05 | |
Nikon D500 | 20.9 | 4.2 | 2.79 | |
Sony 7RMII | 42 | 4.5 | 3.42 | |
Fuji XT-2 | 24 | 3.9 | 1.69 |
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Igual, J. Photographic Noise Performance Measures Based on RAW Files Analysis of Consumer Cameras. Electronics 2019, 8, 1284. https://doi.org/10.3390/electronics8111284
Igual J. Photographic Noise Performance Measures Based on RAW Files Analysis of Consumer Cameras. Electronics. 2019; 8(11):1284. https://doi.org/10.3390/electronics8111284
Chicago/Turabian StyleIgual, Jorge. 2019. "Photographic Noise Performance Measures Based on RAW Files Analysis of Consumer Cameras" Electronics 8, no. 11: 1284. https://doi.org/10.3390/electronics8111284