GIMP - Image - How to keep image quality when reduce image size?

Question

I have a image size 300x300mm resolution 72pixel/in. I want resize it to 120x120mm but keep the quality (by increase resolution?).

First test, I increase its resolution to 180pixel/in then scale it to 120x120 >> image still degrade.

Second test, I increase its resolution to 180pixel/in then scale it to 150x150 >> image still degrade.

Can you help me out? Thanks,

So we can not keep the quality even if we increase its resolution? — Anh-Tuan Mai, Dec 01 '15 at 17:24
If I convert it to TIFF then resize. Does it work? Or may be the conversion degrade the image? — Anh-Tuan Mai, Dec 01 '15 at 17:29
You need to have TIFF at start. JPEG has limited information, it will not help you even you will convert it to TIFF. Look at my answer below, that's the only way (Smart Sharpening). — m.aibin, Dec 01 '15 at 17:31
What about PNG? Can I convert it to TIFF and keep its quality? Thank you so much :) — Anh-Tuan Mai, Dec 01 '15 at 17:42

score 1 · Accepted Answer · answered Dec 01 '15 at 17:27

It's not possible to keep quality if you will resize JPEG or PNG, because the way how the algorithms works. Only if you will work on raw or tiff files, you can change your image size without problems. Using links below you can make it less blurry.

Look here: https://www.gimp.org/tutorials/Smart_Sharpening/ and https://docs.gimp.org/en/gimp-image-scale.html

GIMP - Image - How to keep image quality when reduce image size?

1 Answers1