[BUG] PNG output forced into indexed color

[jeff-bowman]

Since v1.5.0, PNG files that puppeteer-screenshot-tester generates are forced into indexed color (256 color limit).

This appears to be due to the use of quality on lines 117 and 147. As on the sharp PNG docs, setting quality implicitly sets palette to true.

Incidentally, line 93 sets compressionLevel instead of quality and therefore the diff files are properly saved losslessly.

Workarounds

• Roll back to 1.4.0.
• Switch to WebP or another format, though there is no way to specify lossless or nearLossless WebP output.

Fixes

• Switch lines 117 and 147 to set compressionLevel.

• Pass outputSettings or one of its keys directly to sharp's output functions, allowing for passthrough control of Sharp. This could also be specified through something like:

  .png({ quality: outputSettings.compressionLevel || DEFAULT_PNG_COMPRESSION, ...outputSettings.overrides })