Dithering in solid areas when exporting as low-color PNG

[ZanaGB]

As a test with this program i have decided to make a small project to understand the basics of how to handle it. So far so good, until i export the final result into an 8-colour indexed PNG file to save space.

The project has nothing but two colours, white and the background colour, so the remainder of the palette just exists for antialiasing, however, i am finding that on the exported image, all the solid white areas have dithering on them, the edges are correctly antialiased as expected, but the white areas have an irregular pattern on them.

I have provided the project file to someone i know who runs Designer on macOS and on their end, and they seem to have ran into the same problem as i did.

The project settings used are: Preset: None, Palletized: Yes, Pallette: Automatic, Colours: 8, and "Don't export layers hidden by export persona" checked. This is being done in Designer 1.8.3.641

The problem does not exist while exporting as PNG without any additional parameters. Although, SOMETIMES, setting PNG-8 as a render preset will give an image with banding, instead of dithering.

Attatched is a render at the highest resolution and the project file on my PC, also the renders from my friend's Mac for comparison's sake.

Windows 10 Classic Wallpaper.afdesign

Edited May 26, 2020 by ZanaGB
Forgot to add Designer version. Added now.

[Sean P]

Hi ZanaGB,

Thanks for letting us know - I've reproduced that here and will get it passed over to development.

[ZanaGB]

Hello, and thank you!

Please keep me posted if this gets any updates!

[bokchoi]

Hi, just echoing that I'm having a similar problem here; the problem also exists when trying to export simple line-and-fill graphics in Affinity Photo.

White areas seem particularly affected by the Palettized option; I'm also finding that the dithering turns into banding if I use a larger palette. The dithering disappears when exporting without checking the palettized option, but at the cost of a much larger file size.

[ZanaGB]

4 hours ago, bokchoi said:

Hi, just echoing that I'm having a similar problem here; the problem also exists when trying to export simple line-and-fill graphics in Affinity Photo.

White areas seem particularly affected by the Palettized option; I'm also finding that the dithering turns into banding if I use a larger palette. The dithering disappears when exporting without checking the palettized option, but at the cost of a much larger file size.

That does indeed seem to be the same exact bug. I wonder what may be causing it