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Does a “raw” picture convey a divine truth? (Taking “divine truth” here to mean “analog sensor’s signal modulo the specified bit depth and some linear transform

by jakear 5y ago

Does a “raw” picture convey a divine truth? (Taking “divine truth” here to mean “analog sensor’s signal modulo the specified bit depth and some linear transform”)

hypertele-Xii 5y ago
There is no truth. It's lenses all the way down.
Derbasti 5y ago
The raw file contains light level recordings affine to the real scene illumination. (The black point is raised, which is why it's affine, not linear). (Assuming no bright pixels are clipped). Each rgb channel is a filtered spectrum. But note that the color filters are essentially arbitrary, and only roughly correspond to the color filters of your eyes or your screen. Also note that some cameras pre-process even raw data, for example with vignetting correction or noise reduction. Some phones even do image fusion and color correction, then re-rawify the data by mosaicing and linearization.
jillesvangurp 5y ago
The point is that this is not a linear transform. To make the captured raw data look like a normal photo, a number of steps need to happen and several of those steps are about tricking human brains into believing the photo matches what your eyes would have perceived. These steps aren't actually linear because of a dynamic range mismatch between your eyes, the camera sensor and the output medium (screen and paper). It's a game of fitting the captured scene with e.g. 11 stops of dynamic range to an output medium that has maybe 5 or 6 stops of dynamic range in order to trick human eyes with closer to 20 stops of dynamic range into believing what it sees on the print is "real/plausible". That is of course a very subjective process that involves a lot of choices regarding how to shape your curves and compress the available data. Additionally, human brains do "funny" things with colors and actually re-construct/imagine things that aren't there. Getting the white balance and color grading "right" is another set of steps and what is right depends both on the conditions under which you capture the scene as under which conditions you view the end result. Most phone cameras and in camera processing software algorithms for all of this that produce a certain look that is pleasing under most circumstances. But those are basically just a hard coded interpretation of the raw data. The point of post processing is having finer control over that process and the ability to use more expensive/better algorithms.

by jakear 5y ago

Does a “raw” picture convey a divine truth? (Taking “divine truth” here to mean “analog sensor’s signal modulo the specified bit depth and some linear transform”)

hypertele-Xii 5y ago

There is no truth. It's lenses all the way down.

Derbasti 5y ago

The raw file contains light level recordings affine to the real scene illumination. (The black point is raised, which is why it's affine, not linear). (Assuming no bright pixels are clipped). Each rgb channel is a filtered spectrum. But note that the color filters are essentially arbitrary, and only roughly correspond to the color filters of your eyes or your screen. Also note that some cameras pre-process even raw data, for example with vignetting correction or noise reduction. Some phones even do image fusion and color correction, then re-rawify the data by mosaicing and linearization.

jillesvangurp 5y ago

The point is that this is not a linear transform. To make the captured raw data look like a normal photo, a number of steps need to happen and several of those steps are about tricking human brains into believing the photo matches what your eyes would have perceived. These steps aren't actually linear because of a dynamic range mismatch between your eyes, the camera sensor and the output medium (screen and paper). It's a game of fitting the captured scene with e.g. 11 stops of dynamic range to an output medium that has maybe 5 or 6 stops of dynamic range in order to trick human eyes with closer to 20 stops of dynamic range into believing what it sees on the print is "real/plausible". That is of course a very subjective process that involves a lot of choices regarding how to shape your curves and compress the available data. Additionally, human brains do "funny" things with colors and actually re-construct/imagine things that aren't there. Getting the white balance and color grading "right" is another set of steps and what is right depends both on the conditions under which you capture the scene as under which conditions you view the end result. Most phone cameras and in camera processing software algorithms for all of this that produce a certain look that is pleasing under most circumstances. But those are basically just a hard coded interpretation of the raw data. The point of post processing is having finer control over that process and the ability to use more expensive/better algorithms.