Gamma adjustment of RAW files

[Abitconfused]

Does gamma correction of RAW images occur in the camera or when a RAW file is opened by post-production software?

[dje]

Ed I believe it's in the pp software. You might be interested in my recent thread and Colin's explanations.

Dave

[Abitconfused]

OK, then, Gamma is applied in Camera Raw at 2.2. This correction, as I understand it, is to accommodate human perception of brightness not necessarily to match monitor contrast. Although, the monitor should be adjusted to a gamma of 2.2 as well. So it is safe to say that a RAW file IS exactly what the sensor receives...true?

[dje]

OK, then, Gamma is applied in Camera Raw at 2.2. This correction, as I understand it, is to accommodate human perception of brightness not necessarily to match monitor contrast. Although, the monitor should be adjusted to a gamma of 2.2 as well. So it is safe to say that a RAW file IS exactly what the sensor receives...true?

Ed I think you could say that in most cases, the RAW file image data is straight out of the sensor A/D converter. However I believe Nikon and maybe one or two other maunfacturers do offer a compressed version as an option.

As for your other point about human perception and display gamma, I wish I could answer that but I can't. The more I read on this matter the more I get confused. There are a lot of debates on this topic on the web, some of them quite heated !

What I can say with some confidence is that the gamma correction applied during processing has to be there to compensate the display gamma otherwise the picture would be too dark. However there are arguments about where human perception comes in which I just cant get a handle on.

Dave

Dave

[Abitconfused]

Thanks Dave, I think sometimes that those who know the perfect answer just aren't talking and spend their time filing patent applications.

[John Morton]

Does gamma correction of RAW images occur in the camera or when a RAW file is opened by post-production software?

I believe the answer is "both" because the straight Analogue-to-Digital conversion from the sensor data to the RAW file has to be corrected to make it 'viewable' in that the actual RAW data is very dark and lacking in contrast (according to those who have actually seen such files as they really are straight from the sensor).

So, there are adjustment curves being applied - which produce the 'viewable' JPEG image seen on the camera's display, rendered in the camera's histogram, and thumbnailed when the RAW file is downloaded to a computer; but, these adjustments are 'parametric' and not permanent so the whole process of using a RAW converter is about adjusting these in-camera parameters and replacing them with settings chosen by the photographer rather than defaulted to by the camera.

[dje]

I believe the answer is "both" because the straight Analogue-to-Digital conversion from the sensor data to the RAW file has to be corrected to make it 'viewable' in that the actual RAW data is very dark and lacking in contrast (according to those who have actually seen such files as they really are straight from the sensor).

So, there are adjustment curves being applied - which produce the 'viewable' JPEG image seen on the camera's display, rendered in the camera's histogram, and thumbnailed when the RAW file is downloaded to a computer; but, these adjustments are 'parametric' and not permanent so the whole process of using a RAW converter is about adjusting these in-camera parameters and replacing them with settings chosen by the photographer rather than defaulted to by the camera.

John good point about the jpeg. As you say, there is a jpeg produced in camera (even with raw shooting) which is used for camera display and is also embedded in the raw file. The jpeg would have the normal processing including gamma. However I dont believe there is normally any gamma encoding done to the main raw data that comes out of the camera.

Dave

[Macmahon]

OK, then, Gamma is applied in Camera Raw at 2.2. This correction, as I understand it, is to accommodate human perception of brightness not necessarily to match monitor contrast. Although, the monitor should be adjusted to a gamma of 2.2 as well. So it is safe to say that a RAW file IS exactly what the sensor receives...true?

For me, the authority on this stuff is Jeff Schewe. His book "The Digital Negative" is worth reading.
What he says is that RAW capture is linear (and from the point of view of the physics of a sensor "simply counting photons" that makes sense.) He says "One of the first jobs raw converters perform is converting the linear capture to a gamma-encoded space to make the captured levels more closely match the ways our eyes see them." Whether the gamma is 2.2 or not depends on the colour space you convert to. sRGB? 2.2 . Adobe RGB? 2.2 . ProPhoto RGB? 1.8
However, whatever colour space the RAW is first converted to, it must be converted again in some application to the monitor's space for you to view it. Almost all monitors are profiled to a 2.2 gamma colour space.
Cheers
Tim