CTL Script: "Relative Color Filter for WB and primaries correction"

[yasuo (Ohnishi, Yasuo)]

Hi,
I made my second CTL script, named “Relative Color Filter for WB and primaries correction”. It operates as front-end color filter for Alberto’s WB and primaries correction CTL script. ART has already local editing color filter based on hue value or ΔE in RGB. But this script operates in the other way based on relative RGB value. It is basically same with my previous CTL script , “Relative Color Area Correction”.

It contains 2 scripts, relcolfilter_wb.ctl and _wbchmix.ctl. Former is main script of this filter and latter is same as Alberto’s wbchmix.ctl except ART_main being disabled. And relcolfilter_wb.ctl needs _wbchmix.ctl and _artlib.ctl in same directory for operating.

CTL scripts cannot control ART’s local editing mask function, but this CTL script emulate local editing mask in ART.

https://drive.google.com/file/d/1L2yF2OwYxB1ZFOlz2xR_binku0c7HHoE/view?usp=sharing

How to use:

You may download this tool from above link, and copy them in your ART’s ctlscripts directory. You can select this tool from color / tone correction.

And you can see following dialog.

Select the target color, and check “Show target area” on. Then move the pivot, skew, strength slider for adjusting editing area. If you check “Apply uniform strength” on, editing effect will be same in target area.
After deciding editing area, check “Show target area” off, and you use other sliders for color editing.
Color editing effect of this tool is softer and smoother than the effect of “Relative Color Area Collection” tool.

Example.
In following image, grass and tree green is too bluish, and I would like to change green area to more yellowish.

First, select target color green, and check “Show target area” on.

But editable area is too narrow, so with skew and pivot slider make the area broader.

And to exclude some areas, use local editing mask in ART.

After deciding editing area, check “Show target area” off, and use other sliders for color editing.

[paulmatth (Paul Matthijsse)]

Hello Ohnishi,

I tried your new CTL script and it seems to work (very) well, so thank you! But I’ll need some more time for testing/playing to see what it really can do. Perhaps more than I can think of at this moment…

One question though, you wrote:

@yasuo

CTL scripts cannot control ART’s local editing mask function, but this CTL script emulate local editing mask in ART.

But one can create an area mask in ART and apply any CTL script on that mask alone, isn’t it? Or do I misunderstand something?

@yasuo

Color editing effect of this tool is softer and smoother than the effect of “Relative Color Area Collection” tool.

I can confirm that !

[yasuo (Ohnishi, Yasuo)]

@paulmatth

But one can create an area mask in ART and apply any CTL script on that mask alone, isn’t it? Or do I misunderstand something?

Yes.
However, I needed a color selection tool (mask) based on a completely different method.

My starting point is editing to remove uneven color cast across different hue regions from film scanned images.

Normal (uniform) color casts are generally easy to remove using existing image editing software. However, it is very difficult to remove uneven color casts across different hue regions like following image. You can see uneven yellow cast in the image.

Figure 1 Uneven yellow cast image

One reason for this is that the hue values ​​of each color region in a color cast are very different from each other. You may see a single color cast area, but it is a sort of illusion. The second reason is that most color selection tools in image editing software are based on ΔE or hue values, a kind of “absolute” value. It is not appropriate to select this type of color cast.

I selected the uneven yellow cast using the existing tools and the results are shown below.

Figure 2 With parametric mask

Figure 3 With color similarity mask

I can select only some part of the yellow cast.

To remove uneven color cast with existing tools, you must split the color cast region into multiple color regions and create an edit instance for each color cast region. It’s very complicated and difficult.

My color selection tool allows me to select the yellow cast all, but some parts must be excluded.

Figure 4 With my color selection tool

The difference in color selection is due to the following reasons: Existing color selection tools are based on ΔE or hue values, a kind of “absolute” value. My color selection tools are based on the difference in r, g, and b values ​​within a single pixel, a kind of “relative” value. The difference between “absolute” and “relative” values ​​results in different color selection.

My color selection tool is not perfect, but it is more useful than existing color selection tools for this kind of editing. Only ‘relative’ value-based color selection tool can select color area across different hue regions, and it is lack or insufficient in existing image editing software in common.

That’s why I stick at my own mask function.

[paulmatth (Paul Matthijsse)]

Thank you @yasuo for your detailed explanation. I understand better now what you meant with the masks and why you need to have your own.

[Urtaur (Javier Pérez)]

Elegant tool!

[yasuo (Ohnishi, Yasuo)]

Thank you!

[yasuo (Ohnishi, Yasuo)]

I have updated this tool. You can download it from following link.

relcolfilter_wb_v2.zip

I have rearranged items on dialog and added some parameters as same as “Relative Color Correction” tool.

Also added a tool tip to the “Skew” parameter. Therefore, this version must be used with ART Ver.1.21.1 or later.