Histogram / RAW conversion comparison

[neuroanatomist]

I see nothing about the histo using a log scale. Am I just missing it? I'd like to make this knowledge useful but I don't understand how it helps me...

I think the rationale for using a base-2 log scale here is simply to convert the luminance data to 'stops' - i.e., a change of one unit means a doubling of the intensity of that pixel.

Are the units you referred to the spaces between the vertical dotted lines? Moving the Brightness slider to the right, from 0.0 to 1.0, moves the tones to the right but not an entire "unit" to the right

The units are the numbers along the bottom; the dashed lines are every two units. So, changing the brightness sliderfrom 0.0 to 1.0 for your image will move the largest peak on the histogram from about -1.0 to about 0 (a change of one unit).

Does the first 3 spaces on the left being so much skinnier than the rest of them have anything to do with anything? Why are they so much narrower? Why is one of the dotted lines in bold? And what's with the gray sections at either end? Are they aesthetic only? But then why are 3 of the units in the gray sections?

The spaces on the left aren't narrower, the dotted lines are still every two units. The solid line at -9.0 isn't a division, that's the black point of the histogram; it's actually a moveable slider - you can drag it, and when you drag it into the portion of the histogram with pixels you'll see the contrast of the image change.


The dotted line at 0.0 is bold because that's the 'origin' - in this case, I believe that zero point is middle (18%) gray as the camera would meter it.


The gray zones at either end aren't just aesthetic - they represent areas of the histogram that fall outside the dynamic range of your camera's sensor. You shot this with an original 5D, correct? That has a 12-bit sensor, while newer cameras have 14-bit sensors which gives them a wider dynamic range. You can see that represented in a comparison of the DPP RAW histogram for a 40D (14-bit) vs. 5D (12-bit):





Hope that provides some clarity - I have not idea why nothing along these lines are in the help documentation.