Yalantis/uCrop · error · CImgIOException

save_jxl(): Failed to set color encoding when saving file '%

Error message

save_jxl(): Failed to set color encoding when saving file '%s'.

What it means

After setting basic info, save_jxl() configures the color encoding to sRGB (gray or color) via JxlEncoderSetColorEncoding. If libjxl returns non-success, CImg closes the file, destroys the encoder, and throws CImgIOException, because a JXL stream cannot be produced without a valid color encoding.

Source

Thrown at ucrop/src/main/jni/CImg.h:61877

        basicInfo.num_extra_channels = 1;
      }
      basicInfo.num_color_channels = nChannels;
      if (JXL_ENC_SUCCESS!=JxlEncoderSetBasicInfo(encoder,&basicInfo)) {
        cimg::fclose(file);
        JxlEncoderDestroy(encoder);
        throw CImgIOException(_cimg_instance
                              "save_jxl(): Failed to set basic info when saving file '%s'.",
                              cimg_instance,
                              filename);
      }

      JxlColorEncoding colorEncoding = {};
      JXL_BOOL isGray = pixelFormat.num_channels<3?JXL_TRUE:JXL_FALSE;
      JxlColorEncodingSetToSRGB(&colorEncoding, isGray);
      if (JXL_ENC_SUCCESS!=JxlEncoderSetColorEncoding(encoder,&colorEncoding)) {
        cimg::fclose(file);
        JxlEncoderDestroy(encoder);
        throw CImgIOException(_cimg_instance
                              "save_jxl(): Failed to set color encoding when saving file '%s'.",
                              cimg_instance,
                              filename);
      }

      JxlEncoderFrameSettings* frameSettings = JxlEncoderFrameSettingsCreate(encoder,NULL);
      if (JXL_ENC_SUCCESS!=JxlEncoderSetFrameDistance(frameSettings,distance)) {
        cimg::fclose(file);
        JxlEncoderDestroy(encoder);
        throw CImgIOException(_cimg_instance
                              "save_jxl(): Failed to set lossy compression level when saving file '%s'.",
                              cimg_instance,
                              filename);
      }
      if (JXL_ENC_SUCCESS!=JxlEncoderAddImageFrame(frameSettings,&pixelFormat,(const void*)rgbBuffer._data,
                                                   rgbBuffer.size())) {
        cimg::fclose(file);
        JxlEncoderDestroy(encoder);

View on GitHub (pinned to f788b534b4)

Solutions

1. Save with a standard channel count (1 for gray, 3/4 for RGB(A)); convert the image first: img.resize(-100,-100,-100,3).
2. Rebuild against a current libjxl so JxlEncoderSetColorEncoding behaves as CImg expects.
3. Ensure JxlEncoderSetBasicInfo succeeded with a channel layout consistent with the pixel format (isGray flag matches num_channels<3).

Example fix

// before
img.save_jxl("out.jxl"); // img.spectrum()==2, inconsistent with gray/color setup
// after
img.resize(-100, -100, -100, 3); // normalize to RGB
img.save_jxl("out.jxl");

if (img.spectrum() != 1 && img.spectrum() != 3 && img.spectrum() != 4) {
  img.resize(-100, -100, -100, 3); // normalize so color encoding setup is consistent
}

try {
  img.save_jxl("out.jxl");
} catch (const cimg_library::CImgIOException &e) {
  std::fprintf(stderr, "jxl color encoding failed: %s\n", e.what());
  img.save_png("out.png");
}

When it happens

Trigger: save_jxl() on an image where the pixel format's channel count implies gray but the encoder state disagrees (or vice versa), or a libjxl build/state where the color-encoding step fails after basic info was accepted.

Common situations: Mismatch between basic info (set earlier) and pixelFormat.num_channels — e.g. custom channel layouts; incompatible or very old libjxl versions lacking API/behaviour expected by CImg.h.

Understand the failure class

Background: "API request failed": what wrapped HTTP errors from external APIs mean and how to find the real cause — this error's family across 29 libraries.

Related errors

• load_jxl(): Failed to configure decoder '%s'.
• save_jxl(): Failed to set basic info when saving file '%s'.
• load_jxl(): Unable to load data from '(FILE*)' unless libjxl
• load_jxl(): Failed to get file size '%s'.
• load_jxl(): Failed to load image data '%s'.

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/fec06d289e3851ac. Report an issue: GitHub.