JPEG image is "blocky"

[oliver-moran]

First, thanks very much for your library, which I am using in Jimp. Without this library and pngjs Jimp would not be possible.

An issue was raised about the picture below being "blocky" when it is decoded (especially the blurry background elements): jimp-dev/jimp#134

A test case using Jimp is as follows:

var Jimp = require("jimp");

Jimp.read("image.jpg").then(image => {
    image.quality(100).write("out.png");
});

If I convert the image to a PNG using GIMP and perform the same test on that image then the issue doesn't present. For that reason I think the issue lies here.

[ArmorDarks]

Hm, seems like library no longer maintained...

[benwiley4000]

Thanks @oliver-moran, and sorry for the delayed response. Could you confirm this issue still exists after recent updates?

[hipstersmoothie]

@benwiley4000 I'm a maintainer on jimp and running @oliver-moran code with the image. Blocky-ness seems to be gone now!

[benwiley4000]

Cool!

[hipstersmoothie]

IDK if it's fully fixed though. I found another issue where encoding and decoding right after one another produces a slightly different image.

const fs = require('fs')
const jpeg = require('jpeg-js');
const jpegData = fs.readFileSync('./exampleImages/npm.jpg');
const rawImageData = jpeg.decode(jpegData);
const jpegImageData = jpeg.encode(rawImageData, 100);

const Jimp = require('jimp')

fs.writeFileSync('./out.jpg', jpegImageData.data)

I know it's not super noticable, but if you zoom in on the u in you the pixelation around the letters gets slightly darker

Input:

Output:

[benwiley4000]

Ok I'll reopen

[hipstersmoothie]

It almost looks like its grouping together 4 pixels and only using 1 color from the 4

[patrickhulce]

The original issue may have been related to and partially fixed by #25 if they were progressive JPEGs. If not, probably separate issue we should try to hunt down :)

Given jimp-dev/jimp#121, it seems like it's still definitely on the decoding side not encoding side?

[hipstersmoothie]

yeah that makes sense since it happens when just decoding and then encoding to another format