slow performance vs img2sixel

[Alsan]

when the image size is small, almost the same between gosr and img2sixel, but when the image size is large, ie: 2560x1920, gosr and img2sixel are 4.44s and 04s respectively.

i use the following two commands for test:

cat /tmp/t.png | time gsor -
img2sixel /tmp/t.png

[Alsan]

and when i resize the image to a smaller size, it works fine again.

cat /tmp/t,png | time gosr -resize 640x480 -

0.58s used.

[mattn]

Since sixel need to work with, primary colored imagesCurrent implementation makes paletted images dynamicly . If it use palette.Plan9 or palette.WebPage, it become bits more faster. (But rough colored images may be generated.)

I pushd fix branch. fix branch provide two flags -dither (default true) and -palette (default medan).

$ cat image.png | gosr -dither=false -palette=webpage

This become more faster.