Hi,
I made another new Python plug-in for GIMP3. This plug-in apply Sigmoid curve to the selected layer parametrically. You can download it from below link.
If you install it, you can start it from [color] menu.
It duplicates original target layer and applies edits on the duplicated layer.
You can adjust the applying curve with Contrast, Symmetric Point, Darkest Point (Black point), Brightest Point (White point), and you can easily confirm the shape of the curve on the dialog.
The default calculation mode is legacy mode (the curve calculation is performed in perceptual RGB space), however you can switch it to linear mode (the curve calculation is performed in linear RGB space).
I have updated this script. In this version, you can select curve graph display mode from “Perceptual” and “Linear”. And also I added mid point and symmetry point marker on X axis.
If you select “legacy” as “Calculation space”, it calculates the curve in perceptual TRC encoded space, and with “linear”, it calculates the curve in linear color space. If you select “specify Gamma”, you can adjust the Gamma of the calculation color space with slider.
I have internationalized this plug-in (ver. 2.0). In this version, I provide following language translation files.
CatalĂ
Deutsch
Español
français
Italiano
Japanese
Korean
Magyar
Nederlands
Polski
Translation files are “locale” directory under this plug-in’s directory.
Even if your language is not included this list, you can easily make your language locale file. Throw “defaut.txt” in locale directory to online AI translation service, and save the result as [your language code].txt in locale directory. For example, you would like to add Vietnamese translation, save the result as vi.txt in locale directory. You can find the list of language code in [Edit] > [Preferences] > [Interface]>[Language].
And if you use Mac OS, please set your language explicitly in preferences and do not use system language setting. Otherwise my plug-in will be displayed in English.
Run the Sigmoid curve plug-in and check each channel image using target channel selector. You must check what channel has the highest or lowest mean value or standard deviation.
In this image, R channel has highest mean value, you must correct the R channel first. And it seems that B channel mean value is relatively low, so, in next, correct the B channel.
In this plug-in, basically using Sigmoid correction to change the image brightness level. So to lower the R channel level, you must move IP to 100.0 and change contrast value as far the R level becomes similar level with other channels.
After once complete the editing process and correct the R channel, you run this plug-in again to correct the B channel level. In this turn, you set the IP under 50, but not 0, because it seems that in highlight it is needed to raise the blue lever but in shadow it is not needed to raise it.
In the result image it seems that concrete parts is too bluish, so to diminish the blue cast in those parts, you make blue mask with he relative RGB color mask maker plug-in and edit the mask to cover the concrete parts.
Colors => Levels, I select Channel Red, because that is the Color Cast, now White Point Selection for all channels, I click near the Master Point. I set the sliders Channel Red, observing the displayed values in the Reference Point and visually
