I receive 3 Png file but one looks grainy when zoom in but the other looks ok. I check the resolution is the same. So what is the causes of the quality. Although there is different in document size, but when compare a smaller document size with same resolution also looks grainy. Anyone can explain the issue? Thanks.
The "grainy" PNG is in indexed color mode. The reason for this is that the creator of it likely used the "Save For Web" option in Photoshop and saved it as a PNG-8, using fewer than 256 colors.
Depending on the quality you desire, there are a few options you can ask them to do (in order from smallest file size/lowest quality to highest):
- Redo "Save For Web" and increase the number of colors on the PNG-8 to 256
- Redo the "Save For Web" and save as a PNG-24 instead of PNG-8
- Use the regular "Save As" option and select "None" under compression
I would go with the last option, as it will provide you with the highest quality PNG. You can worry about compressing it yourself, after you've done your work with it.