Encode function should accept an explicit palette for writing ctype = 3 PNGs about upng.js HOT 3 CLOSED

Hi, we wanted users to avoid such low-level work with images. I recommend to do following steps:

Convert your image to RGBA8 format (4 bytes per pixel). Then, use UPNG.encode() with cnum=0 (lossless compression).

UPNG uses palettes whenever possible, to save space. So it will store the image with a palette (ctype=3). Since you asked for lossless, the palette will be identical to yours. Only the colors within a palette may be reordered.

from upng.js.

I am aware of this option, but it requires an unnecessary quantize step.

from upng.js.

There is no quantization inside UPNG during the lossless mode. It just finds unique colors again, and puts them into palette. It should not take more than 3 milliseconds of time and 4 MB of RAM for a 1Mpx image.

You can also prepare the input for UPNG.encode._main, but it is not documented anywhere.

from upng.js.