This ideally belongs in the 2D forum, but I don't think anyone is reading there...

I've got some huge medical illustrations in black and white. They're sort of schematic, with lots of lines and text labels. The originals range from 2000x2000 to 4000x4000, and I don't have access to other versions. I need to bring them down to about 400x400. None of the resizing methods in Paintshop or Irfan are satisfactory. The main drawing is OK but the text is blurry. Is there a resizing algorithm that is known to work better in this situation?

I don't think so, basically what you do is to reduce the amount of information in the image which required 4000x4000 pixel to suddenly fit in a 400x400, so you loose a lot of information (details). The only way to improve the details of the text is to add it after you have resized the images so it is made to fit the 400x400 size. But regardless of how you do it, small text on a 400x400 will always look blurred simply due to the lack of pixels in the image, so its a matter of just trying different font sizes until you are happy..

Okay. Erasing and re-adding the text is what I've been doing. I was hoping there was a lazier way, but I guess not.

Thanks for the explanation!

Not a 2d solution but how would they come out if you loaded them to a square in Poser, turned off filtering and rendered it at the desired size from an orthogonal camera?

Good idea. Tried it, and it's a little better than Irfan's best resizer. Not dramatically better. I expect there's just no magic solution here, and I'll have to do it the hard way.

you can turn pixilation off in gimp when you resize.

In the scale box you put "none" in the Interpolation ,I think.

I have no idea why you need something as small as only 400 pixels. why so small ?

scaling in steps might help ? 4000 to 2000 to 1000 to 400

Raster to vector software? It sucked twenty five years so probably still sucks now but if you're feeling lucky.... comparison

Never use Vectors never even think of them but ya if it's a simple picture. I never used this but online looks fast n easy https://vectr.com/

Next time probably ask on a photoshop forum. We only think in 3D

Going down to 400x400 pixels is a terrible idea if there are fine lines and other details such as text, 400x400 represents a tiny amount of visual information and is useless for any other purpose than a low-res preview: but if that's what you're after, read on.

If the images are _literally _black and white (rather than grayscale), convert them to bitmap mode (i.e. where each pixel is either black or white) _before _reducing the size. This should avoid any anti-aliasing artefacts (which is probably what's causing the blurry text), but this process (pixel decimation) is going to be hit-or-miss as far as retaining the detail you want.