Created attachment 114766 [details] Gwenview's rendering The same PNG file was rendered quite differently on Gwenview and Okular. See the attachment for detailes
Created attachment 114767 [details] Okular's rendering
Looks like a transparent PNG for which Okular shows a white and Gwenview a dark background. Maybe Settings > Configure Gwenview > Background color helps?
I don't think this is a bug; rather, the PNG has transparency and Gwenview has multiple options that Okular doesn't when it comes to how to render PNGs with transparency. As Peter says, Settings > Configure Gwenview > Background color will give you all the options you could ever want for how to render the transparent parts--including choosing the same bright white color that Okular uses.
Yes, I can adjust the background color to make the PNG file seems OK. But why the default settings use such a dark background. I tested the same file on Mac and Windows but did not anticipate that it was due to background color.
The default setting is to use the same color for transparency as the rest of the background, which I think makes a certain amount of sense. For this particular image, I'm guessing you would have liked the previous default setting--which was a checkerboard pattern--even less. :)
Created attachment 114785 [details] Background color adjusted Do you mean the background color can adjust automatically? I slide the button to the right. Now the PNG looks good
That's one way. Another way is to go to the Image View tab and change the background type there.
Thanks! Got it. Maybe the default settings should use a less tricky way like surrounding color with a light color. Firefox, Mac and Windows image viewer takes this way.