[v1.104] JPEG decoding with dithering

[XnTriq]

1. Go to Settings → Load format settings… → Read.
2. Set DCT to Floating.
3. Set Dithering to None.
4. Convert a JPEG to PNG.
5. Repeat the conversion with Dithering = Ordered.
6. Repeat the conversion with Dithering = Floyd-Steinberg.

The resulting PNGs are identical

[Xn User]

Which method compression in JPEG file was be used ? This very need for report , I mean what 1x1 1x1 1x1 or 1x2 1x1 1x1 or 2x2 1x1 1x1 )
And test was be do with classic JPEG compression methods or JPEG LI compression methods ?

[XnTriq]

testorig.jpg

Encoder: libjpeg
Chroma subsampling: 4:2:0 (2×2,1×1,1×1)

[xnview]

testorig.jpg
Encoder: libjpeg
Chroma subsampling: 4:2:0 (2×2,1×1,1×1)

if i check the code of libjpeg, it seems that dithering is only used when quantize with colormap

[Xn User]

Right , Dithering must be do use only for 1x2 1x1 1x1 or 2x1 1x1 1x1 or 2x2 1x1 1x1 , for 1x1 1x1 1x1 dithering not need use )
I also asked in JPEGLi https://github.com/libjxl/libjxl/issues/4146 , you can see what XnView MP and ACDSee Pro 5.0 with IDE_ACDstd 5.0.56.0000 reading file with differ , in result XnView MP with Floyd-Steinberg colors a little rude if compare with ACDSee Pro , I see rude gradients

[Xn User]

Please , add all this algorithms https://surma.dev/things/ditherpunk/ and will be learn which is better
In the end will better if this algoritms will be apply optionaly to all lossy or images with less colors
this for testing methods of dithering https://surma.dev/lab/ditherpunk/lab.html

[XnTriq]

Related: Ximagic Quantizer