convert error in this png about cgbi-to-png

[jakubknejzlik]

Hi, I’m not sure what’s the issue. Is it the cgbi in zip archive cannot be converted to png?

[dos1in]

The test code is

const cgbiToPng = require('cgbi-to-png');
const fs = require('fs');

var cgbiBuffer = fs.readFileSync('./AppIcon.png');
var pngBuffer = cgbiToPng.revert(cgbiBuffer);
fs.writeFile('target.png', pngBuffer, function(err) {
    if(err) {
        return console.log(err);
    }
    console.log('The file was saved!');
}); 

[dos1in]

Hi, does this problem have a solution?

[jakubknejzlik]

Hi @JChord sorry for the delay. I can reproduce this in tests, also checked the PNG and script logging. The difference I've noticed is that png you provided has iCCP colour profile, which could be cause of the problem. Do you know the xcode version that generated the ipa file? It's also lighter than the test file:

AppIcon.png:

chunk type (start: 8)
chunk type (end: 23): CgBI
chunk type (start: 24)
chunk type (end: 48): IHDR
chunk type (start: 49)
chunk type (end: 2626): iCCP
chunk type (start: 2627)
chunk type (end: 19085): IDAT
chunk type (start: 19086)
chunk type (end: 19097): IEND

Test png file:

chunk type (start: 8)
chunk type (end: 23): CgBI
chunk type (start: 24)
chunk type (end: 48): IHDR
chunk type (start: 49)
chunk type (end: 64): gAMA
chunk type (start: 65)
chunk type (end: 77): sRGB
chunk type (start: 78)
chunk type (end: 121): cHRM
chunk type (start: 122)
chunk type (end: 478): iTXt
chunk type (start: 479)
chunk type (end: 499): pHYs
chunk type (start: 500)
chunk type (end: 539): iDOT
chunk type (start: 540)
chunk type (end: 19667): IDAT
chunk type (start: 19668)
chunk type (end: 38484): IDAT
chunk type (start: 38485)
chunk type (end: 38496): IEND

AppIcon.png after exporting it from macos preview app:

chunk type (start: 8)
chunk type (end: 32): IHDR
chunk type (start: 33)
chunk type (end: 2616): iCCP
chunk type (start: 2617)
chunk type (end: 2973): iTXt
chunk type (start: 2974)
chunk type (end: 19369): IDAT
chunk type (start: 19370)
chunk type (end: 24060): IDAT
chunk type (start: 24061)
chunk type (end: 24072): IEND

Exported output from AppIcon.png using library:

chunk type (start: 8)
chunk type (end: 32): IHDR
chunk type (start: 33)
chunk type (end: 2610): iCCP
chunk type (start: 2611)
chunk type (end: 21849): IDAT
chunk type (start: 21850)
chunk type (end: 21861): IEND

Also could you provide original png file from project sources?

[jakubknejzlik]

The best guess right now is the difference in iCCP format of IDAT package. The script (rewritten from python) "shuffles" back the RGB values (they are in reverse order in cgbi) which is correct way for sRGB, but may not be correct for iCCP.

[chenquincy]

@jakubknejzlik I get this issue too. Can this problem be solved?

Here is the original png file: png file

[jakubknejzlik]

Hi @chenquincy, thanks for your report. Unfortunately I currently don't have time budget to investigate this issue, but pull requests are always welcome.

[SagePtr]

Both failed images are interlaced. So it looks like interlaced images are not yet supported at this moment, the row lengths are not necessary 1 + width*4 in them as the pixels are rearranged.

Also, in the code the image is assumed to be 8bit RGBA, i have no idea what types are really supported in that Apple's proprietary format, R/B channels swap should not happen for some kind of the images (for instance, for grayscale).