How to render best raw highlight clipped indication?

[KarlMagnusLarsson (Magnus Larsson)]

Hello RT experts,

How to render best raw highlight clipped indication, using existing RT functionality, up to RT-dev in git?

Is this the best approach, or can it be improved?:

1. processing profile → Neutral
2. color management → No profile
3. Clipped highlight indication → on

I would like to find the best way to mimic a RAW histogram highlight clipping indication. The RAW histogram is good, but I would like to connect any raw clipped pixels to the picture.

I use RT built from git source on Debian testing.

[Thanatomanic (Roel)]

Interesting question. I think a little more is required:

1. Processing profile → Neutral
2. Color Management
   a. Input Profile → No profile
   b. Working Profile → ACESp0
   c. Abstract Profile → Linear g=1
3. White Balance → Turn off
4. Preferences (first page) → Clipping Indication → Threshold for clipped highlights → 255
5. Clipped highlight indication → Turn on
6. Toggle through the red/green/blue channels to show individual clipping

Edit: if you do these steps, the regular histogram will strongly resemble (but not be identical to) the raw histogram. But I believe this gives a very good indication where the raw channels have clipped.

[KarlMagnusLarsson (Magnus Larsson)]

@Thanatomanic Thank you for the input. I plan to add these steps to a processing profile for easy checking.

I did the steps you indicated whilst checking the effect on clipped highlight indication.

Aha, White balance! Good catch. Of course!

I added “gamut button → on” to let the clipping respect the working profile you propose. I have added to the list.

While it is nice to have an ordered list with step numbers, I suppose that the ordering is not important? I changed to a bullet list to indicate that.

What is the purpose of “Working Profile → ACESp0” and “Abstract Profile → Linear g=1”?

• Processing profile → Neutral
• Gamut button (Editor) → on
• Color Management
  • Input Profile → No profile
  • Working Profile → ACESp0
  • Abstract Profile → Linear g=1
• White Balance → Turn off
• Preferences (first page) → Clipping Indication → Threshold for clipped highlights → 255
• Clipped highlight indication → Turn on
• Toggle through the red/green/blue channels to show individual clipping

Is there more?

[Thanatomanic (Roel)]

@KarlMagnusLarsson

While it is nice to have an ordered list with step numbers, I suppose that the ordering is not important? I changed to a bullet list to indicate that.

Correct.

@KarlMagnusLarsson

What is the purpose of “Working Profile → ACESp0” and “Abstract Profile → Linear g=1”?

The ‘Linear g=1’ setting ensures the data is not ‘gamma-encoded’, but linearly maps the light intensities in the raw file to output pixels. In theory this should not change the amount of clipping, but in a quick test I see that it does slightly. Working with linear data should be preferred if you want to emulate the raw file as close as possible.
ACESp0 is a huge color space, so no gamut-based clipping will occur.

[KarlMagnusLarsson (Magnus Larsson)]

@Thanatomanic

The ‘Linear g=1’ setting ensures the data is not ‘gamma-encoded’, but linearly maps the light intensities in the raw file to output pixels. In theory this should not change the amount of clipping, but in a quick test I see that it does slightly. Working with linear data should be preferred if you want to emulate the raw file as close as possible.
ACESp0 is a huge color space, so no gamut-based clipping will occur.

ok.

@Thanatomanic

ACESp0 is a huge color space, so no gamut-based clipping will occur.

ok. I found a reference here: Academy Color Encoding System - Wikipedia

I wonder if there is another way, or if what I see is just an artifact coincidence, but if I do the steps above and then do:

• RAW → Demosaic → None
• Zoom to 100%

Then I get a similar highlight clip indication compared to before, but with different colors in clipped areas, compared to the black/gray highlight indication. Does “RAW → Demosaic → None” bring us closer to a pure RAW clipping indication? Is what I see just a side effect of something else, or is it an intended feature?

I understand that it is impossible to talk about better/closer RAW clip indication, since I have not offered a mathematical description of what I mean with RAW clipping. I think I mean ‘RAW values at or above white point’, but I am not sure.

[heckflosse (Ingo Weyrich)]

You can use Capture Sharpening mask view to show the areas which are clipped in the raw file.

set the contrast threshold to 1 and enable the mask view. Areas rendered in black are clipped in the raw file

Edit: this method is not 100% correct, because the mask is blurred with a gaussian sigma of 2. But at least you can get an idea where there are clipped areas.

[KarlMagnusLarsson (Magnus Larsson)]

Hello @heckflosse. Your method works fine, for me. It is also easy to switch between methods once all settings are dialed in.

I have added 3 pictures with the different methods. The picture is a flower with the central part blown out. This is also visible in the raw histogram in upper left.

1: Method as proposed by @Thanatomanic. (clipped highlight indicator used).

2: Method as proposed by @heckflosse. (Capture sharpening mask and contrast threshold = 1).

3: Set demosaic → None, magnify to 100% and activate highlight clipping indicator (not visible in regular non magnified view).