Feature/rainbow eraser for color images (#1034)

* Add rainbow_artifacts_eraser helper

This helper file contains the methods necessary to perform a fourier transform on the picture, to remove frequencies responsible for rainbow artifacts on Kaleido screens, and performe the reverse fourier transform

* Replace blurring method with frequency removal method to erase rainbow effect on Kaleido 3 screens

* High performance improvements by using rfft2 instead of fft2

* Fine-tuned the settings and added the perpendicular direction for a better final rendering

The finer settings allow for more information to be retained in the final image, while still effectively removing the rainbow effect.

Adding the perpendicular direction results in a better rendering of the final image (avoiding visual artifacts related to suppression at the main angle).

* Revert the addition of perpendicular angles and lower attenuation_factor

It was a mistake to add the perpendicular angles in the previous commit: I had the rainbow effect removal process called 2 times when I did this, for testing purposes (One before downscale and one after downscale).

The proper way to call the process is only after the downscale. And in this case it is not necessary to remove frequencies along the perpendicular angles.

In the mean time, attenuation_factor=0.15 has proven to work well along a collection of testing images.

It should be my latest commit for this feature

* Also attenuate high frequencies at 45°

CFA is sometimes orientated at 135°, sometimes at 45° so until we find if there is a law depending on the screen size, e-reader model or something, the best we can do is attenuate high frequencies on those two directions

* fix imports

* Update comic2ebook.py

Calculate is_color with (opt.forcecolor and img.color)

pass is_color to img.optimizeForDisplay

* Update image.py

Remove color check condition, because now we process colored images too.

Pass is_color to erase_rainbow_artifacts

* Update rainbow_artifacts_eraser.py

Add support for colored images: Convert to YUV, extract luminance channel, do FFT -> Filter -> IFFT on luminance channel, insert back to YUV, convert back to RGB

To maximize compatibility until we know for sure the orientation of CFA for each device, filtering is now done on 135° + 45° axis

After more testing, attenuation_factor is decreased to 0.10

* Update comic2ebook.py

Rename rainbow eraser param

* Update image.py

rename rainbow eraser param

* Update KCC.ui

Rename rainbow eraser checkbox and tooltip

* Update KCC_ui.py

Rename erase rainbow checkbox and tooltip

* Update KCC_gui.py

Rename erase rainbow checkbox and option

* Update README.md

rename erase rainbow param

* Update KCC_gui.py

correct param name for eraserainbow

---------

Co-authored-by: Alex Xu <alexkurosakimh3@gmail.com>

README.md

@@ -264,7 +264,7 @@ OUTPUT SETTINGS:
   --spreadshift         Shift first page to opposite side in landscape for two page spread alignment
   --norotate            Do not rotate double page spreads in spread splitter option.
   --rotatefirst         Put rotated spread first in spread splitter option.
-  --reducerainbow       Reduce rainbow effect on color eink by slightly blurring images
+  --eraserainbow       Erase rainbow effect on color eink screen by attenuating interfering frequencies
 
 CUSTOM PROFILE:
   --customwidth CUSTOMWIDTH