Histograms

Based on the discussions in the LightZone forum and my own experiments I found that histogram ≠ histogram.

I created in DPP a slightly processed JPG of the same image I used in my previous post. I opened then the JPG image both in DPP and LZ and the RGB histograms were different even the images looked the same. I had earlier assumed that the differences in the histograms were caused by different processing of the raw image, but that is not true. The histograms don't visualize the same thing!

Canon Digital Photo Professional

LightZone

I found a piece of software ImageJ that has an option to copy-paste the channel histogram data into Excel. I then generated a simple channel intensity vs. pixel count chart and that corresponds quite well with the DPP histogram. It looks like the scaling of the y-axis in DPP is not linear, e.g. the first peak in blues is about a third of the highest peak in DPP but in Excel it's about two thirds (200k vs 320k). I tried to change the x-axis to logarithmic so that I could have produced the histogram in LZ, but the result wasn't the same. I guess LZ shows some kind of luminosity vs. channel intensity histogram as the x-axis would indicate.

Linear and logarithmic histograms generated in Excel

Experimenting with different digital darkroom software

I have used a long time Canon's Digital Photo Professional (DPP) for processing my raw images. Sometime ago I found RawTherapee (RT) and used it a little, but wasn't really fond of it. I found the learning curve too steep. Couple of weeks ago I learned about LightZone (LZ) and it has been more to my taste than RawTherapee. In LightZone I have more control of the process than I do in DPP, but LZ is easier to grasp and achieve what you want to than RT.

Today I was trying to create similar styles as DPP has (mainly landscape and portrait) and I found significant differences how the programs process the raw image and found that my task is not going to be that easy.

Here are the images, no additional processing, just "developing" the raw image. Images are taken with Canon 600D, EF-S 18-55mm f/3.5-5.6 IS II (@ 55mm, f/9.0, 1/800s, ISO 200).

Digital Photo Professional

RawTherapee

LightZone

Findings

DPP's and RT's RGB curves look quite similar, but the LZ produces totally different curves. The peaks at the shadows have in LZ moved to midtones and the small peaks at high tones are in LZ significantly higher. In fact the in LZ the highest peaks are at high tones as in the two other programs they are in the shadows. The differences are also visible in the image. The Canon's version of the paint of the tram is faded and worn and in LZ the reds and yellows shine bright. RT is somewhere in between, little emphasing reds, nearer to Canon.

I will continue experimenting.