Color shift when encoding UIImage files

[skochan]

[This was posted as part of another topic, which was closed....not by me). So I moved it here

Here are two images, JPEG and webP. Notice the big color shift. The UIImage that's given to the JPEG and webP compressors is generated from a cocos2D openGL layer that gets rendered into a UIImage. I'm not sure if that's affecting the webP encoder, but as you can see, the color shift is noticeable. Again, If I decompress the JEPG and then recompress with webP, I have no problem--there is no color shift

[newacct]

To reproduce a color shift, take the Demo project, and change the following in ViewController.m:

Change static CGFloat alpha = 0.6f; to static CGFloat alpha = 1.0f;

Add the following lines after UIImage *demoImage = [UIImage imageNamed:imageFileName];:

UIGraphicsBeginImageContext(demoImage.size);
[demoImage drawInRect:CGRectMake(0, 0, demoImage.size.width, demoImage.size.height)];
demoImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

[harryhorn]

@skochan I am seeing the same issue and thanks for the tip to convert it to a Jpeg and only then convert to WebP. like @newacct I am also downscaling the image so now I downscale, convert to jpeg and then to weep. Of course this causes extra processing but solves the issue as a workaround.

[pawelnathan]

I am seeing the same issue here. Has anybody found the reason for this?

[kross51]

This should fix the issue... I attached full file for simplicity... rename as .m :)

UIImage+WebP.txt

[xiaoyao8023]

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