Hi guys, I have a bit of trouble getting my head around linear and non-linear images being generated by Canon's RAW conversion utilities. Canon provides a "TIFF 16bit/channel linear" mode in their RAW conversion software. Is that linear image data what is produced by the image sensor in the camera? Out of curiosity I converted a RAW image to "TIFF 16bit/channel linear" mode and opened it up in Photoshop. It looks really dark. I increased the gamma until it looked pretty much like the same image in "TIFF 16bit/channel" (non-linear) mode. Surprise, surprise... the gamma is about 2.5. I deduce from that that either - the RAW conversion software applies a gamma of 2.5 to every image by default in non-linear mode (likely), or - the nature of the image sensor is such that it applies a gamma of 2.5 and the RAW conversion software applies the inverse gamma to produce the linear mode image (less likely). If the first case is true, doesn't that mean that my great 16bit RAW image is already degraded by the gamma application? Doesn't that mean that certain values in the histogram do simply not occur anymore because they have been "gammaed" together with brightness values in the neighbourhood? One thing may be worth mentioning in this context: When I opened the image in Photoshop I applied the Adobe RGB (1998) profile to it (I _applied_ it, I did not convert the image to it) since that is the color space I usually shoot in and I have my EOS 10D configured as such. However, since color spaces describe the "meaning" of "color numbers", so to speak, that color space can only be the correct color space for either the linear _or_ the non-linear image. I strongly suspect it is correct for the non-linear image since it works fine on JPEGs as well and JPEGs look pretty similar to the TIFFs produced in non-linear mode. I may get a bit disillusioned here about RAW images that I always thought are "a direct image of what the image sensor sees". To complicate the matter even more: Adobe RGB (I always thought, please correct me if I am mistaken) as a working color space is linear. Hence, every image I have on my screen in Photoshop is in a linear color space. By the use of my monitor profile an inverse 2.5 gamma (this is all roughly of course, color profiles contain much more information than that) is applied to the image _only for display_. My monitor then, by its nature applies a gamma of 2.5 to the image when displaying the image, hence the inverse gamma applied by the color management system for display purposes. That is why images in Photoshop just look right on the screen. However, when I _apply_ a linear color space such as Adobe RGB (1998) to an image, I basically tell Photoshop that the image data is linear. Hence, if I apply Adobe RGB (1998) to the linear RAW image it should just look right (but as previously mentioned it looks far too dark). If I apply Adobe RGB (1998) to non-linear RAW image it should look somehow odd depending on the (unknown) nature of the non-linearity (but it just looks fine). It almost seems that the linear image is not linear at all but has a gamma less than 1 (the reciprocal of 2.5) applied to it. But that is probably not the solution, or is it? Sorry for so many words. I thought I better explain the issue in detail. I am curious what others think about all this. Maybe someone knows the answer to all this. Thank you anyway for listening. Malte.
