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12.1 Desensitizing at Development
However, some cameras can record not only the region represented as white when the exposure bias amount is 0, but also brighter region in RAW data. In order to check whether your camera can do it or not, do an experiment with this software as shown below. First, take a picture as the highlighted portion of details that looks brighter continuously will be gone. Then, adjust the "Exp. bias" slider to the - side. At this time, if you see the details appear on the region which has gone when the "Exp. bias" was set to 0, your camera can record the region which looks more brighter than white in RAW data. If you execute this experiment carefully, you can find the breaking point from which details of the highlighted portion do not appear at above a certain exposure bias value. For example, the detail appears at a value up to -1/2EV. However, it will not appear when the value is more than that. At this time, this means that your camera has recorded the RAW data with an allowance of 1/2EV. To put it the other way around, the upper 1/2EV level of sensor's dynamic range has not been used. In some cameras, such function only works when ISO speed is increased. Although the highlighted portion will not be gone up to 1/2EV, it is not good to take a picture by using the region fully. Because linearity may have been lost already in the region. In order to use the region fully, check a test shooting whether its color representation can be achieved to the level that you satisfy. There is no other way in this case. If you know techniques up to this level, for example, in a certain subject, you might create a clean picture with little noise by setting the exposure bias amount as 1/2EV. Refer to '12.2 Linearity and Saturation of Image Sensor.'
However, at a certain level, even the light quantity is increased, the output level of the signal does not increase anymore. This is Saturation. This causes overexposure even on the RAW data. This does not mean that you can use the sensor fully up to right before the saturation occurs. Degradation of color representation occurs when the given light quantity is out of the region where the output signal is proportional to the light quantity. Normally a camera is designed to create a JPEG picture with this proportional region. However, it is not a perfect proportion and it includes allowable range which shows the level that can be allowed at maximum. If the allowable ranges differ between a camera manufacturer settings and your setting, use your own setting. The difference doesn't mean fault of your camera. You just try to adjust the exposure bias toward underexposure until the exposure enters in your allowable range. If this does not work well, that the camera is no good anymore. We recommend you to buy a new one. There is no other way. If you are able to prevent degradation of color representation by taking a picture with underexposure setting, a noise may increase. Since that is a capability of a camera sensor, you have to find a middle ground between the color representation and the noise. In a contrary sense, in a case of some subject, you may set the exposure out of the allowable range of a manufacturer setting. In this case, set overexposure within the range which is described in 'Desensitizing at Development', to obtain a clean picture with little noise. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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