image.transparent
Image is partly see-through. Level: Warning.
When it is raised
Raised for a PNG whose alpha channel or tRNS chunk is declared and whose decoded pixels are at least 1% see-through, counting a pixel as see-through when its alpha is below 250 out of 255. Images under about 900,000 pixels are read in full; larger ones are sampled on an even grid aimed at roughly 400,000 samples. The message gives the percentage to one decimal place below 10% and rounded to a whole number from 10% up. Below 1% the check does not fire.
What it does to a shared link
The see-through areas take whatever colour sits behind the image where it is displayed, and the page cannot choose that colour. og:image has no light or dark variant, so a logo or text drawn for a white background can become hard to read on a dark one, and the reverse.
How to fix it
- Flatten the image onto a solid background colour and re-export it.
- Check the flattened image at the size a card is shown before publishing it.
- Give the new file a new URL so cached copies of the transparent version are not reused.