Steps to reproduce

1.  Follow steps in below link to create the image operation: https://docs.magnolia-cms.com/product-docs/6.2/Developing/Templating/Theme.html#_image_variations
2.  Upload original JPG image
3. Set output format as PNG
4. Set output format > quality as 20

.. Logs, screenshots, gifs...

Expected results

• According to https://docs.magnolia-cms.com/product-docs/6.2/Modules/List-of-modules/Imaging-module.html#_output_format
• An image with 20% quality should be generated

.. Justify non-trivial expectations with a link to a doc or a relevant discussion.

Actual results

• No very different images were generated if we set values in range 0-100

Workaround

• PNG currently being a special case due to our calculation, image quality floating around 5 to 9 according to its compression level. This also depends on our PNG library in used.

Development notes

• Compression level being set in info.magnolia.imaging.DefaultImageStreamer.writePngWithCompression(BufferedImage, OutputStream, OutputFormat)

          PngWriter pngw = new PngWriter(os, imi);
          int quality = outputFormat.getQuality();
          pngw.setCompLevel(Math.max(9 - quality, 5));
  

The calculation shown that just in very narrow range PNG image quality could be in used.