(Kalles Fraktaler) analytic log(DE) post-processed with ImageMagick

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Online claude

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« on: March 30, 2018, 02:34:37 AM »
Mandelbrot set, power 2.  Magnification 7E7 near 1/3 child of 1/3 child of ... 1/3 child of cardioid.  Inspired by Dinkydau's "density near the cardioid" series.

log(DE) colouring, with black far exterior, then rainbow from red to violet, with white interior (none visible).

analytic (derivative-based) DE with jitter, single frame rendered at 6480x9360 with KF-2.13.1 test version (unreleased)

post-processed with ImageMagick to reduce noise and enhance colours:
Code: [Select]
convert dense-large.png -depth 16 \
  -colorspace RGB -channel RGBK -normalize  -blur 7x2 \
  -colorspace YUV -equalize -colorspace RGB -blur 7x2 -resize 50% \
  -colorspace YUV -equalize -colorspace RGB -blur 7x2 -resize 50% \
  -colorspace YUV -equalize -colorspace RGB -blur 7x2 -resize 50% \
  -colorspace YUV -equalize -colorspace RGB -blur 7x2 -resize 50% \
  -colorspace sRGB -depth 8 dense-equalize-yuv.png

excerpt.png is 1:1 rendered pixels straight from KF, cropped to central region

larger version is rendering now, raw image data will be 4x4 frames at 6480x9360 with stratified jitter


Linkback: https://fractalforums.org/fractal-image-gallery/18/analytic-logde-post-processed-with-imagemagick/1118/

Offline gerrit

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« Reply #1 on: March 30, 2018, 07:20:46 AM »
What does the postprocessing do?

Online claude

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« Reply #2 on: March 30, 2018, 07:33:56 AM »
convert # imagemagick program
dense-large.png # read input file
-depth 16 # convert to 16bit
-colorspace RGB -channel RGBK -normalize # convert to linear RGB colourspace (presumably from sRGB with non-linear gamma) and normalize channels (each channel is normalized individually/separately, this changes hues in general)
-blur 7x2 # separable Gaussian blur with radius 7 and sigma 2
-colorspace YUV -equalize -colorspace RGB -blur 7x2 -resize 50% # convert to YUV colour space, perform histogram equalization (of each channel separately, afaik), convert to linear RGB colour space, blur, downscale: these steps are repeated a few times
-colorspace sRGB -depth 8 # convert to 8-bit sRGB (typical colour space for web images)
dense-equalize-yuv.png # save output file

the intent is to equalize colours in a perceptual colour space (YUV) while avoiding noise (by blurring) and avoiding desaturation from blur/downscaling (this is why the equalize/blur/resize 50% is repeated instead of doing it all at once)

without equalization (just gamma-correct downscaling) it looks like the attached.  with typical gimp downscale (not gamma correct) it looks similar, but darker
see https://web.archive.org/web/20121223021721/http://www.4p8.com/eric.brasseur/gamma.html

Online claude

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« Reply #3 on: April 03, 2018, 07:00:04 AM »
here's a higher resolution version post-processed with custom C code (two programs, one for tile assembly beating the 2G element limit of GNU Octave, another for in-place image equalisation beating ImageMagick's excess memory usage).

colours don't look as good as the ImageMagick version imo, still experimenting...


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