libpng warning: iCCP: known incorrect sRGB profile

Question

Libpng-1.6 is more stringent about checking ICC profiles than previous versions. You can ignore the warning. To get rid of it, remove the iCCP chunk from the PNG image.

Some applications treat warnings as errors; if you are using such an application you do have to remove the chunk. You can do that with any of a variety of PNG editors such as ImageMagick's

convert in.png out.png

To remove the invalid iCCP chunk from all of the PNG files in a folder (directory), you can use mogrify from ImageMagick:

mogrify *.png

This requires that your ImageMagick was built with libpng16. You can easily check it by running:

convert -list format | grep PNG

If you'd like to find out which files need to be fixed instead of blindly processing all of them, you can run

pngcrush -n -q *.png

where the -n means don't rewrite the files and -q means suppress most of the output except for warnings. Sorry, there's no option yet in pngcrush to suppress everything but the warnings.

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Binary Releases of ImageMagick are here

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For Android Projects (Android Studio) navigate into res folder.

For example:

C:\{your_project_folder}\app\src\main\res\drawable-hdpi\mogrify *.png

Use pngcrush to remove the incorrect sRGB profile from the png file:

pngcrush -ow -rem allb -reduce file.png

• -ow will overwrite the input file
• -rem allb will remove all ancillary chunks except tRNS and gAMA
• -reduce does lossless color-type or bit-depth reduction

In the console output you should see Removed the sRGB chunk, and possibly more messages about chunk removals. You will end up with a smaller, optimized PNG file. As the command will overwrite the original file, make sure to create a backup or use version control.

Solution

The incorrect profile could be fixed by:

1. Opening the image with the incorrect profile using QPixmap::load
2. Saving the image back to the disk (already with the correct profile) using QPixmap::save

Note: This solution uses the Qt Library.

Example

Here is a minimal example I have written in C++ in order to demonstrate how to implement the proposed solution:

QPixmap pixmap;
pixmap.load("badProfileImage.png");

QFile file("goodProfileImage.png");
file.open(QIODevice::WriteOnly);
pixmap.save(&file, "PNG");

The complete source code of a GUI application based on this example is available on GitHub.

UPDATE FROM 05.12.2019: The answer was and is still valid, however there was a bug in the GUI application I have shared on GitHub, causing the output image to be empty. I have just fixed it and apologise for the inconvenience!

You can also just fix this in photoshop...

1. Open your .png file.
2. File -> Save As and in the dialog that opens up uncheck "ICC Profile: sRGB IEC61966-2.1"
3. Uncheck "As a Copy".
4. Courageously save over your original .png.
5. Move on with your life knowing that you've removed just that little bit of evil from the world.

To add to Glenn's great answer, here's what I did to find which files were faulty:

find . -name "*.png" -type f -print0 | xargs \
       -0 pngcrush_1_8_8_w64.exe -n -q > pngError.txt 2>&1

I used the find and xargs because pngcrush could not handle lots of arguments (which were returned by **/*.png). The -print0 and -0 is required to handle file names containing spaces.

Then search in the output for these lines: iCCP: Not recognizing known sRGB profile that has been edited.

./Installer/Images/installer_background.png:    
Total length of data found in critical chunks            =     11286  
pngcrush: iCCP: Not recognizing known sRGB profile that has been edited

And for each of those, run mogrify on it to fix them.

mogrify ./Installer/Images/installer_background.png

Doing this prevents having a commit changing every single png file in the repository when only a few have actually been modified. Plus it has the advantage to show exactly which files were faulty.

I tested this on Windows with a Cygwin console and a zsh shell. Thanks again to Glenn who put most of the above, I'm just adding an answer as it's usually easier to find than comments :)