[old_tv_nut]

Photoshop tells you the RGB values in its working color space (sRGB, ProPhoto, or whatever you have chosen) which includes a non-linear transfer function, for example, the "gamma correction" in sRGB. It does not tell you linear amounts of red, green and blue light primary colors. Although not strictly logarithmic (like photographic F-stops), it is similar, and makes for useful, readable histograms.

Photoshop is aimed at the needs of photographers and artists, not scientists. Some operations in Photoshop may actually work in linear space (the conversion from one set of primaries to a different set, for exmple) but this is buried in the middle of the process and is not displayed to the user.

Another example of something Photoshop/Camera Raw and Lightroom do without mentioning it is to apply an S-curve transfer function to images. This base curve can be modified by the contrast adjustment. It is essential to getting pleasing photos (as Kodak discovered in the late 1800s), but Photoshop never tells the user what the curve actually looks like. This curve is applied before any Curves adjustment made by the user, so even if you leave the Curves adjustment set to linear, the overall process has an S-curve built in.

There are many other details to photo-editing software that are designed to make the best looking and therefore not scientifically accurate photos, just as was the case with film.

The S-curve both compensates for the reduced contrast impression of the eye when viewing a print as compared to the original scene, and also makes it possible to use a display device or print process with limited contrast range to display a scene that originally had a much higher contrast range, without hard clipping of highlights and shadows.