I use raw histograms in my cameras 6D and 7D (ML) and I would like to use a raw image analyzer like Rawdigger, but of course, something that is open source instead. I found Rawnalyze, but the creater has past away. With raw-based overexposure indicator in Darktable, I am able to see the the same clipped colour channels (with white balance turned off) as I do see in ML raw histograms, but I don´t see the a raw histogram in Darktable.
FWIW, I had a play with Dave Coffin’s DCRAW some time back. It can output a file of the raw pixel values which I loaded into Excel and produced a graph from. I didn’t get as far as doing it per channel, just overall. This was under Windows. The command I used was
dcraw -c -4 -D _6D_2886.cr2 | C:“Program Files”\GnuWin32\bin\pgmhist.exe > outfile.txt
and you can see the CR2 input file and the output going to “outfile”. If I remember this depends on the extra executable PGMHIST to give histogram data. I think DaveC pointed me to that, he was very helpful.
As an example, here is a graph with no. of pixels as Y axis, and along X, a dynamic range of roughly 11.5 stops divided into 250 “bins” (if my maths was correct!) -
((was just going to upload jpeg but website or my browser not working properly…)
Substituting g’mic for pgmhst.exe makes a basic histogram without much fuss:
dcraw -c -4 -D 6D2886.cr2 |gmic -.ppm -display_histogram
The -.ppm tells gmic to slurp the image from stdin, and -display_histogram should be self-explanatory.
The problem with it for your purposes is one of resolution; the image depicts the bins of the raw integer data, but the statistics printed following the command line are in gmic’s 0-255 normalized range. I just played a bit with -display_histogram’s parameters, but I can’t get at anything that in particular tells me the exact values of the bins where the highlights start to bunch up. If someone has used -display_histogram to analyze raw data, I’d be interested in what you did with the parameters…
Dcraw seems to do what Rawdigger does. Is there a tutorial for dcraw with commands to check for example SNR and DR in a image? I use Ubuntu.
I have used RawTherapee for many years, but first today I found the raw histogram. But to me it feels strange that it clips the highlight before the histogram hits the right wall, see my print screen.
RawTherapee raw histogram, hitting an invisible right wall.
Clipped green and blue channels in Darktable. White balance turned off.
Raw histogram straight out and print screened from my 6D. Super flat picture style (doesn’t matter but that’s why it i s pale). 9% of the green channel clipped. 5% of blue channel clipped. Less than 1% of red channel clipped.
_MG_0167.CR2 (25.3 MB)
The white level for your camera is 15180. That’s about 7% less than the theoretical max value for 14 bit files (16383). I guess for that reason the raw histogram does not hit the right wall. To be confirmed by @ilias_giarimis
Thanks. That sounds reasonable.
“Confirmed” … although I am not sure if the histogram shows the clipping after our conservative WhiteLevel setting … if not it’s the “typical” 15283 as mentioned in camconst comment
BTW the histogram clipps out the below Black level values which is around 2048 … and the real difference is more than 7% (16383 - 2048) / (15180 - 2048)