When cameras record data in raw format, they do not record three channels for each pixel. Each pixel only records one channel. When the data is converted from a raw format into a conventional format, the additional channel data is generated based on the color filter array used in the camera. << http://en.wikipedia.org/wiki/Color_filter_array >>
If you're going to be this picky, you ought to admit that at this stage they aren't called pixels, but photosites; the source you link contradicts you on this, hewing to the standard convention. Also, it seems a bit strange that you would only provide a cite for one of the least controversial parts of your statement.
Because values indicate a linear increase in brightness, this range of values allows for the brightest value to be only 254x brighter than the darkest value. Thus the dynamic range of 8-bit data is only 7.989 stops.
While thought-provoking and news to me, this also strikes me as misleading (you do not provide a cite here, which would be very helpful).
Even if values DR=0 and DR=255 denote brightness levels below or above the "measured" dynamic range that do not plot along with those other values in a linear fashion, it is simply missing the point to argue that they are not at least usable parts of the dynamic range of an image and therefore record something of the dynamic range of a scene. Even if full black and full brightness are not "accurate," they provide points of contrast for the final image, and so the usable, not real, DR is barely more than you suggest. It's a bit like asking the color of black or white, and then arguing from the answer that because they aren't technically colors that they cannot be mixed on a palette. If there is some photographer who seriously believes that DR=0 and DR=255 are unreliable (or even worse, useless), they have not spent enough time taking actual photographs.
I also question the assumption that DR always scales in a linear fashion. Silicon is peculiar and, as evidence of this, the DxO data shows that DR (as it is represented in RAW files, at least) falls off in a non-linear fashion when ISO is raised
. In fact, there doesn't appear to be any set relationship at all.
Even if the sensor was originally able to record a wider dynamic range, any data from that larger range is discarded along with the bits that recorded it. Some data loss can be avoided by using a non-linear value system. With the gamma correction of 1, Photoshop bends the curve to get 14 stops of dynamic range out of the 8 bit space.
You act as if Photoshop has done something scurrilous. No, my friend, the fact that "Photoshop" (in truth, every type of image processing software, including the camera manufacturer's RAW converter, those of third party makers, and that done in-camera) can get "14 stops" means that there are, in fact, 14 stops compressed (in a linear or non-linear matter hardly matters; you run into similar issues in color switching your camera from sRGB to Adobe RGB) into that 8 bit space. The camera, and the camera's RAW and any third-party RAW converters, have to set or assume a floor, ceiling, and steps (or a "curve," though I suspect that in many cases there is no actual function, but instead something analogous to a look-up table for quick transcribing and interpretation of brightness levels). Just because the steps are coarser or finder does not mean that the top inside value cannot represent a shade nearly 14 stops, or 9 or 31 or 1000, brighter than the lowest. The 8-bit value is, in truth, arbitrary.