generate anti-aliased tiles in a second slow pass

[Linden6]

When zooming out of a canvas textured painting aliasing is very apparent - as below.

I know from early discussions on 'issues' that one approach mooted was to 'use subsample for a quick zoom out, then shrink for a slow (or very slow) high-quality pass when the viewer is idle'. Was this ever implemented? Thanks.

[jcupitt]

Hi again, yes the aliasing can be annoying.

As a workaround, you can save images in a pyramidal format, and then view that. The best one is probably tiled pyramidal TIFF -- do "save as", then select this set of options:

ie. jpeg, tiled, pyramid. Now when you view, open will be instant, and you'll get beautiful anti-aliasing.

File size is roughly similar:

$ ls -l st-francis* 
-rw-r--r-- 1 john john 145314456 May  9  2023 st-francis-interlaced.jpg
-rw-rw-r-- 1 john john 227612475 Sep 17  2020 st-francis.jpg
-rw-r--r-- 1 john john  96074898 Nov  1  2022 st-francis.jxl
-rw-r--r-- 1 john john 150253546 May 14 11:33 st-francis-q75.jpg
-rw-r--r-- 1 john john 205468577 May 14 11:29 st-francis.tif

Though of course it depends on the Q setting.

[Linden6]

Thanks for this.

I've just converted a large ~1GB jpeg image into a pyramidal tiff, and am unfortunately finding it less responsive to navigate than the original jpeg - zooming in and out is quite jerky. It also took about 15 seconds to load, which isn't exactly instantaneous.

Also, I converted the previous image where the aliasing was particularly prominent, and aliasing is still quite noticeable - presumably as levels of zooming between pyramidal levels.

[jcupitt]

Huh strange. Did you tick the tile option?

Here's that Bellini as a tiled pyramidal JPEG TIFF. Open is instant, zooming is fast and smooth, anti-aliasing looks nice:

http://www.rollthepotato.net/~john/st-francis.tif

[jcupitt]

I forgot to say, if you are building your own vipsdisp, you should also build libvips master (8.17). It has quite a few fixes to improve rendering. The flathub vipsdisp is built against 8.17.

[Linden6]

My apologies, I was accessing the large ~1GB image file over a network (limited to about ~10MB/s). Once I copied the file to my local drive and tried again it did open almost instantaneously.

I built Vipsdisp against vips-8.16.1. I will recompile against 8.17 and see if the aliasing issue persists. Thanks.

[jcupitt]

You were probably being hurt by the latency -- TIFF files have a lot of seeking, and you will have had to round-trip to the network drive for each one.

The aliasing should have been OK though. Did you see aliasing in the Bellini image too?

[Linden6]

I've recompiled vipsdisp against libvips-8.17.0-test4 and converted the image with prominent aliasing to a pyramidal tiff file, which can be found here:
https://we.tl/t-3SpQslCsH8

Unfortunately, as below, aliasing is still noticeable. Thanks.

[jcupitt]

Wow haha I see. Your Monet really is an extreme example of moire.

I'll see if I can improve the way this is handled, it looks like it might be possible.

[jcupitt]

That commit on nip4 makes it a lot better. I'll add it to vipsdisp too, or you can, of course.

[jcupitt]

... and I added this to vipsdisp master and credited you in the changelog. Thanks for the horrible test case!

[Linden6]

That's a great improvement - many thanks!

[Linden6]

Although you closed this issue, I'm thinking that perhaps it should be left open. We now have a good workaround, but aliasing persists with conventional - i.e. non-pyramidal tiff - image files. Thanks.