Brad Wolff recently wrote a comment on my earlier post, “Change of plans – here comes Paint.NET v3.5” :

“Rick – You mentioned that 3.5 will have “Improved rendering quality when zoomed in”. Can you elaborate on this? My fear is that we will end up having to look at the blurred mess that Windows Picture Viewer displays when zoomed in. Please tell me I am wrong!” — Brad Wolff

Brad, you’re wrong 🙂 And it’s in a good way. Paint.NET v3.5 does not use bilinear or bicubic resampling when zooming in, which is the cause of the blurred mess that you mention in Windows Picture Viewer. In fact, it is now using the same resampling algorightm for zooming in that has been employed for zooming out: rotated grid supersampling. The old resampling method was the simple nearest neighbor one. It was very fast, especially when paired with a lookup table for avoiding a per-pixel division operation. The image quality problem with nearest-neighbor is very apparent between 101% and 199% zoom levels: you end up with a moire of 1-pixel wide and 2-pixel wide samples and it just looks awful. With supersampling, we are able to achieve a smoothed look that does not blur as you zoom in.

Here’s an example from Paint.NET v3.36, where I’ve drawn a normal circle and some scribbles with the paintbrush tool. The zoom level was then set to 120%:

Here’s the same, but in Paint.NET v3.5:

At this zoom level, each pixel from the image should be drawn as “1.2” pixels on-screen. In v3.36, this entails drawing 4 pixels at 1-pixel width, and then a fifth pixel at 2-pixel width. Put another way, every 5th pixel is doubled in size. In v3.5, each source pixel ends up with a uniform width and the overlaps are smoothed together in a much more pleasing manner. (This is done on the y-axis as well — replace ‘width’ with ‘height’ in the preceding paragraph and it’s also true.) It will still maintain a “pixelated” appearance as you continue zooming in, which is what you want, but the edges between samples will look smoother.

This does come at a performance cost, but I believe it’s worth it. It also scales well with multiple cores, so it’s something that will be faster with each new CPU upgrade. I’ve also experimented with using bilinear and bicubic resampling — it’s fun, but too expensive and blurry. You would need an 8-core system for it to be comfortable.