Managing clipping

[kpz]

I have my highlight warning indicator activated with the preferences set to defaults, so it shows red pixels when at least one channel is at 250 or above in RGB.

However, I do not understand how the levels tool works in relation to this. I mapped the value 255 to 249, presumably preventing any clipping. Yet I still see red pixels. Why is this? It occurs even after zeroing out all other adjustments (unless I missed one...).

[fdisilvestro]

Hi, you adjusted only the combined RGB. You need to do it for every channel (R, G, B)

[kpz]

edit: deleted because of incorrect information.

[kpz]

I investigated more and it seems this is a bug. When I adjust from below (moving up to 249) it has the expected behavior. Further, I cannot find a pixel that is actually 250 or above in any channel in the attached screenshot. So it must be some problem with the clipping warning rendering, not the actual computation of RGB values.

Is there a way I can report this to Phase One?

[Bart_van_der_Wolf]

I investigated more and it seems this is a bug. When I adjust from below (moving up to 249) it has the expected behavior. Further, I cannot find a pixel that is actually 250 or above in any channel in the attached screenshot. So it must be some problem with the clipping warning rendering, not the actual computation of RGB values.

Hi, I don't think this a bug. The input controls (under the histogram) allow to change the Raw data's clipping, but the output controls (above the histogram) then take the end-result and maps that to the limits given. The output controls are not intended to adjust clipping.

BTW, there are better tools to address clipping. In particular, the combination of a Luminosity masked layer and e.g. the HDR highlight tool works wonders.

Is there a way I can report this to Phase One?

In general, you can file a support ticket (link is near the bottom of the page) at:
https://www.phaseone.com/en/SupportMain

Cheers,
Bart

[digitaldog]

The best tool for examining actual clipping, not clipping due to some rendering of the raw, is RawDigger. Actual clipping is something you want to avoid through actual exposure (assuming you are clipping data you don't wish to clip, again through actual exposure which is solely an attribute of aperture and shutter).


https://www.rawdigger.com

Articles on exposing for raw:
http://www.onezone.photos
http://schewephoto.com/ETTR/
https://luminous-landscape.com/the-optimum-digital-exposure/
http://digitaldog.net/files/ExposeForRaw.pdf
https://www.fastrawviewer.com/blog/mystic-exposure-triangle
https://www.fastrawviewer.com/blog/red_flowers_photography_to-see-the-real-picture
https://www.rawdigger.com/howtouse/exposure-for-raw-or-for-jpegs
https://www.rawdigger.com/howtouse/calibrate-exposure-meter-to-improve-dynamic-range

[kpz]

Hi, I don't think this a bug. The input controls (under the histogram) allow to change the Raw data's clipping, but the output controls (above the histogram) then take the end-result and maps that to the limits given. The output controls are not intended to adjust clipping.

BTW, there are better tools to address clipping. In particular, the combination of a Luminosity masked layer and e.g. the HDR highlight tool works wonders.

Sorry, reading this and Andrew's answer makes me realize I'm being imprecise with my language. Thank you both for the correction.

Let's suppose I want to force all pixels to be at most 249 in all RGB values.

If I set the output control at 249 as in the screenshot, and the highlight warning at 250, then I reason I should see no highlight warning, since all pixels should have their R, G, and B channels mapped to 249 or less. Yet I see a highlight warning. Why is this?

I could not actually find a pixel with a channel mapped to 250 or more, though perhaps I was not searching hard enough, which made me think the red warning pixels were a bug. It is quite possible I'm wrong.

[Bart_van_der_Wolf]

Sorry, reading this and Andrew's answer makes me realize I'm being imprecise with my language. Thank you both for the correction.

Let's suppose I want to force all pixels to be at most 249 in all RGB values.

If I set the output control at 249 as in the screenshot, and the highlight warning at 250, then I reason I should see no highlight warning, since all pixels should have their R, G, and B channels mapped to 249 or less. Yet I see a highlight warning. Why is this?

In my reasoning, the clipping indicators point to Raw data being clipped, either by over- or underexposure, or e.g. by pulling in the input controls at the bottom of the Levels dialog. Whatever these input controls are set to, the range between the minimum and maximum is mapped to the output range that you can set in the upper output controls..

So, originally, input level 0 is mapped to output level 0, and input level 255 is mapped to output level 255. When you lower the input controls to 250, then everything between 250 and 255 will be clipped to 250. In both cases, your setting of the highlight warning to 250, will show the same clipping warning, but only if you set the input control to 250 will the clipping really take place.

The output mapping takes whatever is offered as range, e.g. 0-255 or 0-250, and maps all those input pixel values in the range to the output values you set in the upper controls of the Levels dialog. It does not change the clipping of the input data, it just changes the output levels mapping.

I think this is working as designed.

Cheers,
Bart

[kpz]

My apologies, but while that makes sense I'm not sure how it explains the phenomenon I'm seeing.

The highlight warning shows pixels with an "output" of at least 250 (in any channel). You agree that the top slider controls the maximum output level. Hence, with the top level slider set to 249, no pixel should have an output value of 250 or greater. So the highlight warning should never trigger.

Where is the problem with this reasoning?

(I agree my question actually has nothing to do with "clipping" in the sense of raw data capture saturating.)

[32BT]

My apologies, but while that makes sense I'm not sure how it explains the phenomenon I'm seeing.

The highlight warning shows pixels with an "output" of at least 250 (in any channel). You agree that the top slider controls the maximum output level. Hence, with the top level slider set to 249, no pixel should have an output value of 250 or greater. So the highlight warning should never trigger.

Where is the problem with this reasoning?

(I agree my question actually has nothing to do with "clipping" in the sense of raw data capture saturating.)

I understand your question and think it is a reasonable question. I don't believe that clipping warning has anything to do with the input data. From the looks however, it suggests there is indeed additional processing taking place in the form of sharpening or similar (lens optimisation?) Which pushes edge pixels back over the limit. So perhaps turning off sharpening, detail enhancement, and lensprofile adjustments etc will help.