![]() ![]() But as the Signal dips into the shadows the camera’s noisier ADC input results in SNR worsening faster. Same IQ as ISOless in HighlightsĪt base ISO such a system records highlights like its ISOless counterpart does, all else being equal. This effectively reduces the information carrying capacity of this system by two stops from 14 to 12 bits (photographers would call it Dynamic Range, in stops). ![]() This means that for a given Exposure the photosites can collect more information about the scene than the electronics are able to process into raw data in one go. Figure 2: Simplified Scene Information Transfer in a Non-ISO-Invariant Imaging System at base ISOĬontrary to the situation in the earlier ISOless case, where the noise floor* of each stage was the same or lower than at the photosites, by the time the signal of this imaging system as set up reaches the ADC and related circuitry the noise floor is two stops higher than at the photosites. Non ISOless: Downstream DR Lower than Sensor’sįor a given exposure this is the path that faces scene Information collected in the non ISO invariant range of a digital camera on its way to being converted to digital numbers and written to the raw file. Many cameras do not actually work like this, but in many cases this model represents a decent and intuitive approximation. Refer to the earlier article for a more in-depth description of the diagram above and remember that this is a simplified model chosen for ease of getting the point across. As do kings of darkness such as the Sony a7S or Nikon D5. Most Canon DSLRs fall into this category today. Such cameras are sometimes improperly referred to as ISOful. The photographer can in such a case choose out of the full information available at the photosites what smaller subset of it to store in the raw data by the selection of different in-camera ISOs. In this article we’ll look at a class of imagers that are not able to store the whole information available at the photosites in one go in the raw file for a substantial portion of their working ISOs. Figure 1: Simplified Scene Information Transfer in an ISO Invariant Imaging System at base ISO All digital cameras become ISO invariant above a certain ISO, the exact value determined by design compromises. Cameras that are considered to be (almost) ISOless from base ISO include the Nikon D7000, D7200 and the Pentax K5. It is able to do so because the information carrying capacity (photographers would call it the dynamic range) of each subsequent stage is equal to or larger than the previous one. For a given Exposure the best information quality (IQ) about the scene is available right at the photosites, only possibly degrading from there – but a properly designed** fully ISO invariant imaging system is able to store it in its entirety in the raw data. We’ve seen how information about a photographic scene is collected in the ISOless/invariant range of a digital camera sensor, amplified, converted to digital data and stored in a raw file.
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