libpng warning: iCCP: known incorrect sRGB profile

Question

I'm trying to load a PNG file using SDL but the program doesn't work and this error appears in the console

"libpng warning: iCCP: known incorrect sRGB profile"

Why this warning appears? what should I do to solve this problem?

Answer 1

some background info on this:

Some changes in libpng version 1.6+ cause it to issue a warning or even not work correctly with the original HP/MS sRGB profile, leading to the following stderr: libpng warning: iCCP: known incorrect sRGB profile The old profile uses a D50 whitepoint, where D65 is standard. This profile is not uncommon, being used by Adobe Photoshop, although it was not embedded into images by default.

(source: https://wiki.archlinux.org/index.php/Libpng_errors)

Error detection in some chunks has improved; in particular the iCCP chunk reader now does pretty complete validation of the basic format. Some bad profiles that were previously accepted are now rejected, in particular the very old broken Microsoft/HP sRGB profile. The PNG spec requirement that only grayscale profiles may appear in images with color type 0 or 4 and that even if the image only contains gray pixels, only RGB profiles may appear in images with color type 2, 3, or 6, is now enforced. The sRGB chunk is allowed to appear in images with any color type.

(source: https://forum.qt.io/topic/58638/solved-libpng-warning-iccp-known-incorrect-srgb-profile-drive-me-nuts/16)

Answer 2

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 ImageMagick's mogrify *.png, provided that your ImageMagick was built with libpng16 (run convert -list format | grep PNG to be sure of that).

If you'd like to find out which files need to be fixed instead of blindly processing all of them, you can run my 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:\AndroidProjects\{your_project_folder}\app\src\main\res\drawable-hdpi\mogrify *.png

Answer 3

After trying a couple of the suggestions on this page I ended up using the pngcrush solution. You can use the bash script below to recursively detect and fix bad png profiles. Just pass it the full path to the directory you want to search for png files.

fixpng "/path/to/png/folder"

The script:

#!/bin/bash

FILES=$(find "$1" -type f -iname '*.png')

FIXED=0
for f in $FILES; do
    WARN=$(pngcrush -n -warn "$f" 2>&1)
    if [[ "$WARN" == *"PCS illuminant is not D50"* ]] || [[ "$WARN" == *"known incorrect sRGB profile"* ]]; then
        pngcrush -s -ow -rem allb -reduce "$f"
        FIXED=$((FIXED + 1))
    fi
done

echo "$FIXED errors fixed"

Answer 4

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 :)

Answer 5

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.