DPP: RAW vs RGB White Point Setting

Well, I have this underexposed portrait open in DPP (top screenshot), the color picker reading 208/127/114 off the cheek.

I choose to adjust the white point. Under the RAW tab, I draw the right border of the histogram to the left. The color picker now reads 252/169/151 (middle screenshot).

I reset the RAW histogram border to its default end position, switch to the RGB tab and again draw this histogram's right border to the left, until the color picker reports the same value for the red component as it did for the RAW tab edit (R=252, bottom screenshot), but the full reading is now 252/171/158. Compared to the RAW tab edit, the green and blue component values went up higher here, producing a substantial saturation reduction as well as more contrast.

I would appreciate if anyone explained to me why this happens and how to put that difference of response to good use.
I know there is an informative 1-hour video on DPP, but that would take a week to download over this lousy internet connection of mine.

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I'm not going to be able to help you at all but I do have a question at the risk of sounding completely ignorant, where the heck do you get the color picker?? I'm using DPP 3.9.2 and I can't find it anywhere.

Go into DPP's preferences, go to the Tool Palette section, and set the Tone Curve to RGB. Try this again and I'll bet you get the same result between the RAW and RGB tabs.

The picker is Colour Watcher, a separate utility, very handy and free. It reads values off the screen, therefore, when playing with pictures saved in different color spaces, you should be aware that the picker reports values as converted to the monitor's gamut.

http://www.broadhurst-family.co.uk …/TheColourWatch​erTool.htm


When I did the test above, the Tone curve mode was set to Luminance RGB. If I change that to RGB RGB, the issue remains unchanged.

In both Tone curve modes, though, the RGB readings perfectly match between Brightness edit and White point edit, when either is done under the RAW tab.

This is my guess at an explanation: The histogram on the RAW tab represents the state of the data after WB but before gamma correction tone curve and profile (Picture Style) are applied. This is deduced from the fact that changing the WB causes the histogram to change, while changing P.S. or clicking the Linear box have no effect on it. Whether the histogram is from before or after demosaicing is unknown, but at any rate P.S. application is done together with gamma correction by applying separate curves to each channel and varying them slightly to emphasize one color or another or to affect saturation. In Neutral/Faithful curves are closer to one and another, but there are still differences that reflect the profile for the particular model. The RGB tab manipulates data in a later stage in the workflow, post-P.S. In other words, there are differences in the relationships between the color channels in the data used by the RAW tab and the rendered data used by the RGB tab.

Rereading my post above, it seems very technical and perhaps confusing to newbies who may read this. So let me simplify it to the statement, the RAW tab works on RAW data and the RGB tab works on rendered data that is ready to be saved as a jpg or a tif. They are different.

Thanks agedbriar, I'll check it out. Love your screen name.

agedbriar wrote in post #11202974
When I did the test above, the Tone curve mode was set to Luminance RGB. If I change that to RGB RGB, the issue remains unchanged.

In both Tone curve modes, though, the RGB readings perfectly match between Brightness edit and White point edit, when either is done under the RAW tab.

"Tone curve mode" makes a *big* difference for the "RGB tab" curve.
I still think this is at least contributing to the issue (the "RGB tab adjusted" image looks like it has an edited curve in luminance mode, definitely not RGB mode.)

Easiest way to check is to Ctrl+Click on the histogram in the RGB tab and switch from "Luminance" to "RGB". Then you will see the change immediately. Otherwise you (probably) need to restart DPP.
Gave it a try on an underexposed image of my girfriend and the difference is huge. I could post the image here, but then she'd kill me. So if anyone needs an example, I'll see if I can find another image

Here's a discussion about the differences between Raw and RGB tab: http://forums.dpreview​.com …32&thread=34659​692&page=1
Also mentions the curves work different.
On page 2 it is also mentioned:

I tend to agree with that, at least where the right/top/bottom are concerned...

Oh, and some more DPP (3*.8 ) tutorials by Eddie Tapp:
http://www.usa.canon.c​om …ArticleAct&arti​cleID=1228

There's also one on "RAW & RGB Histograms" (Haven't watched it yet)

Edit: Watched it, nothing new.

Elie,

I think I pretty much understood your explanation, but I redid the original exercise with Picture style Standard, and the differences in RGB values between the RAW and RGB white point edit are about the same as in Faithful, not bigger.


René,

Indeed, previously, I didn't restart DPP. Following your advice to access the parameters by clicking on the RGB histogram (it's right-click on the PC), I can see the difference in the histogram display, but if I adjust the white point to match the R value to what the RAW adjustment produced, the G and B values still don't match. Under Luminance RGB, G and B are higher than from RAW, under RGB RGB they are lower (by about the same amount) - never the same triplet that the RAW edit produced.

I have read before about that advice to leave the borders of the RAW histogram alone. However, the tests I have done in connection with this topic seem to indicate that adjusting the white point on the RAW histogram gives the cleanest (brightness-only) result, with less impact on saturation and contrast than an equivalent adjustment on the RGB histogram, regardless of Tone curve mode, has.

Thanks for the link to the discussion in dpreview, it looks promising.

agedbriar wrote in post #11205709
Elie,

I think I pretty much understood your explanation, but I redid the original exercise with Picture style Standard, and the differences in RGB values between the RAW and RGB white point edit are about the same as in Faithful, not bigger.

René,

Indeed, previously, I didn't restart DPP. Following your advice to access the parameters by clicking on the RGB histogram (it's right-click on the PC), I can see the difference in the histogram display, but if I adjust the white point to match the R value to what the RAW adjustment produced, the G and B values still don't match. Under Luminance RGB, G and B are higher than from RAW, under RGB RGB they are lower (by about the same amount) - never the same triplet that the RAW edit produced.

I have read before about that advice to leave the borders of the RAW histogram alone. However, the tests I have done in connection with this topic seem to indicate that adjusting the white point on the RAW histogram gives the cleanest (brightness-only) result, with less impact on saturation and contrast than an equivalent adjustment on the RGB histogram, regardless of Tone curve mode, has.

Thanks for the link to the discussion in dpreview, it looks promising.

So, it makes some sense that the RGB levels are going to adjust the color channel levels in a different way than the luminance/Raw tab levels. The RGB adjustments will among other things directly affect channel saturation and channel luminance in a different way from just using say the Brightness slider or the white point slider in the Raw tab. I'm just guessing because I don't have any in-depth DPP understanding, but it seems to reflect what I've seen from playing around.

Thanks for your replies, guys.

With what you and Anonimo on dpreview said in mind, I'm now just playing with the commands and observing how the picture and the various tools displays react. Seeing things that eluded me when I was just intent to get the pictures right.

I'm looking forward to the optical network, now under construction here, finally getting operative, so I can enjoy those videos as well.