How to extract the darkest and lightest value

Here you go

https://filterforge.com/filters/8512.html

Thanks a lot, Sphinxmorpher. I have looked at your filter, and looked again, and again but I don't get it. Sorry.

My guess is that the part that I need starts with the Minimum just after the'Assemble RGB'. Instead of the Result of 'Assemble RGB', I put my image or Noise that has values >1 and/or <0 into the Minimum component. The part I don't get, is the 'Extract R' and 'Extract G inverse'. Are these the highest and lowest values in the image?

I see where the culprit is why it's not working for HDR : the Maximum and Minimum components are not made for HDR.

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For now just divide/multiply the input by a reasonable range (e.g. Input / 1000 -> Auto Levels -> Output * 1000)

I would like to work more precise, so really getting the highest and lowest value from the HDR image to do exact scaling. The LookUp component would do, if only it would know at which coordinate to sample. Dividing by 1000 (even by 10) makes things less precise. With an addition of two NOT HDR images, I can never get bigger than 2. With other operations I might. So I'd really like a image dependent scaling divisor.

The problem is even a bit more complicated for values <0. There I need to add the biggest negative value, so I get to a minimum of 0. Then get the highest value and do the division.

I was surprised that the Maximum- and Minimum Level components are only working on the input image, and we are not able to plug it in somewhere down the line. That would solve the thing and be very handy in a lot of cases.

Sphinxmorpher, thanks for your time and effort,
Beat

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About the inverted G value - if you apply Minimum on an inverted image and then invert the result you get the Maximum. So it is really just an optimization to avoid two bitmap based components (i.e. a maximum and a minimum - they are slow).

I get it now. I am still thinking to basic and havn't paid too much thoughts about optimizing. I am already glad if I get going what I intend to - and learn about the different components. It's really great toying with this stuff.

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I started working on a HDR version - but I'm having some difficulties with the internal precision of the Minimum and Maximum components.

I noticed too, that the Minimum and Maximum components cannot work with HDR. I also noted that with normal (LDR) signals, I sometimes have to put in up to 3 or 4 max components in sequence to get an even grey value (Radius of all of them at 100).

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That is very expensive and actually quite difficult with subsampling taken into account too

Please forgive me if I talk nonsense, I am really new to FF, but I think that extracting the max or min value would only need a sampling once of all pixels, so no subsampling needed here. We would need 2 components like Maximum Level and Minimum Level (from the External category), only with a map input.

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Actually it might be an idea for the renderer - we already have an option for clipping HDR values before subsampling. It would be useful with a "Scale HDR to LDR". Of course that wouldn't help in intermediate processing steps when constructing a filter.

That's it exactly. I am trying to do just that, scaling the HDR into the LDR range. If there would be or become in future such a component, that would be great. In the meantime we have to come up with 'a cunning plan'

Please keep me updated of anything you might find and thanks for your kind help.

Beat

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Sphinxmorpher wrote: I think you're better off rendering your intermediate HDR result to a new file/tab and the use the build in input min/max to scale in a second processing step. Get the idea?

Okay, that was a bad advice. It turns out that even the Minimum/Maximum Level components in the External category does not support HDR. This makes it impossible to convert HDR to LDR in FF in a manner that scales the complete HDR range into LDR. Ouch. I'll add an entry to the wish list.