Understanding Tone Processing and Local Contrast

[theDavid]

Hi, 

 

I have question about the Tone Mapping Persona tools which I really love. I would like to better understand what is happening under the hood when using Tone compression tool and Local Contrast.

 

Usually for realizing what some tool does I use SliceTool in Nuke, which shows me what is happening with the curve after using the tool. On images below we see what tonemap tools do to the curve of the linear gradient ramp. Some results are pretty crazy like when local contrast is combined with Tone Processing. 

 

 

 

 

 

 

 

 

I thought that if I apply same curve as I got from Tone Processing with a normal Curve Adjustment I will get same result, which is not truth. Here is an example.

 

 

 

 

 

 

I would like to know what is happening to the image under the hood with Tone Processing and Local Contrast. I am curious if this effect is possible to replicate with other adjustments or tools. For example lately I use 3DLut Creator with Affinity, I am interested if this effects are possible to recreate with tools in 3DLut Creator and save it to .cube file. If anybody knows more about this topic please enlighten me.

 

[James Ritson]

Hi theDavid, sorry this topic has gone unanswered for so long, I've had a little mull over your questions and done some experimentation. It is indeed possible to replicate similar tone mapping/tone compression using Photo's Curves adjustment, but you have to experiment with the min/max range. I've attached some screen grabs showing the before/after of a Curves adjustment with different min/max setups. It can always use further tweaking though - just placing another node or moving an existing one has a huge impact tonally. On the interior example I also used a Shadows/Highlights adjustment just to pull back that blue sky tone in the window.

 

I've also managed to achieve some similar results by duplicating the pixel layer several times and running variations of a laplacian kernel on each one using the Custom Blur filter (it's just a convolution matrix grid). I don't think these target the kind of result you're after though, but there are various white papers available on local laplacian filtering as a method of tone mapping.

 

In truth, I'm not sure exactly what happens behind the scenes (I could only offer half-guesses really, that might involve gaussian and laplacian filtering), that's best left to a developer to answer accurately. Hope that helps!

[anon1]

Hi theDavid, sorry this topic has gone unanswered for so long, I've had a little mull over your questions and done some experimentation. It is indeed possible to replicate similar tone mapping/tone compression using Photo's Curves adjustment, but you have to experiment with the min/max range. I've attached some screen grabs showing the before/after of a Curves adjustment with different min/max setups. It can always use further tweaking though - just placing another node or moving an existing one has a huge impact tonally. On the interior example I also used a Shadows/Highlights adjustment just to pull back that blue sky tone in the window.

 

I've also managed to achieve some similar results by duplicating the pixel layer several times and running variations of a laplacian kernel on each one using the Custom Blur filter (it's just a convolution matrix grid). I don't think these target the kind of result you're after though, but there are various white papers available on local laplacian filtering as a method of tone mapping.

 

In truth, I'm not sure exactly what happens behind the scenes (I could only offer half-guesses really, that might involve gaussian and laplacian filtering), that's best left to a developer to answer accurately. Hope that helps!

Could you make a tutorial about the in out points of the curves adjustment please?

And also about some options using custom matrix calculations

 

That would be terrific

 

Thanks in advance