Region rounding error between different scales

[petrsloup]

When requesting 2 images with identical region but different scale, slightly different region is returned:

http://iiif.klokantech.com/demo.jp2/2048,0,2048,2048/pct:12.5/0/native.jpg
vs
http://iiif.klokantech.com/demo.jp2/2048,0,2048,2048/pct:25/0/native.jpg

(Notice the y in Copy on the right edge.)

The same can be observed here:
http://iiif.klokantech.com/demo.jp2/2048,0,2048,2048/pct:12.5/0/native.jpg
vs
http://iiif.klokantech.com/demo.jp2/3584,1024,512,512/pct:50/0/native.jpg

(The regions are different, but should be aligned on the right side.)

[klokan]

Can we review this and possibly implement a fix for https://github.com/klokan/iiifserver-build/ @MartinMikita?

[klokan]

I checked the OpenSeaDragon - it makes request like: http://demo.iiifhosting.com/iiif/1/6144,4096,1024,1024/256,/0/default.jpg
but it seems to be exactly the same...

[petrsloup]

Yes, the issue is identical even for fixed image size:
http://iiif.klokantech.com/demo.jp2/2048,0,2048,2048/256,/0/native.jpg
http://iiif.klokantech.com/demo.jp2/3584,1024,512,512/256,/0/native.jpg

[petrsloup]

The problem happens in both IiifViewer and OpenSeaDragon

• IiifViewer -- http://iiif.klokantech.com/demo.jp2/info.json
• IiifViewer -- http://demo.iiifhosting.com/iiif/mona_lisa/info.json
• OpenSeaDragon -- http://iiif.klokantech.com/demo.jp2/info.json
• OpenSeaDragon -- http://demo.iiifhosting.com/iiif/mona_lisa/info.json

The problem is much harder to see with the Mona Lisa dataset. I can actually see it only in OpenSeaDragon -- is it working ok in IiifViewer?

[MartinMikita]

http://iiif.klokantech.com/demo.jp2/2048,0,2048,2048/256,/0/native.jpg
http://iiif.klokantech.com/demo.jp2/2052,0,2048,2048/256,/0/native.jpg
http://iiif.klokantech.com/demo.jp2/2056,0,2048,2048/256,/0/native.jpg

IIPServer is using round() to resize view port (region) for calculated resolution.

First and second image are same, after 8 pixels region is moved by 1 pixel (2048 / 256).