Regression in the quality of bitmap interpolation

[Guillermo Espertino (Gez)]

I downloaded inkscape-devel_0.47~pre3~nightly9.04-8589-1_amd64.deb, and I found that the quality of the bitmap interpolation dropped considerabily compared to pre2.
I'm attaching a screenshot of the differences between both builds.

Notice that the histograms displayed have nothing to do with the problem itself. They do not belong to the image. The histograms are screen captures from GIMP that I'm using for a presentation about histograms.
The problem is the poor quality of the interpolation of the scaled bitmaps.

These samples were taken from a PNG export, but the quality is the same on inkscape canvas.

[Pablo Trabajos (pajarico)]

Guillermo: please upload SVG and files. I think this has something to do with non integer coordinates and dimensions. The output resolution has some effect too.

[Pablo Trabajos (pajarico)]

Oh, nevermind. I thought the upper screenshots were the originals and the pictures at the bottom were too blurry for your test.

[Guillermo Espertino (Gez) (gespertino-gmail)]

Pablo, no it's the opposite. The top image shows the poor interpolation with missing pixels, and the bottom the previous behavior, more visually pleasant.
Could you please confirm this bug?

You can use the same image I attached. It is easy to spot the problem during the scaling.

[su_v (suv-lp)]

Could this be related to the patch for bug #168384?

[Guillermo Espertino (Gez) (gespertino-gmail)]

Hardly. The build I'm using is earlier.

[Guillermo Espertino (Gez) (gespertino-gmail)]

hmmm, but maybe it is. The build is from Sept. 14th, which is the date of the first "fix released" notice.

[ScislaC (scislac)]

Gez: Will you please try with https://edge.launchpad.net/~inkscape-nightly/+archive/ppa/+files/inkscape-devel_0.47~pre3~nightly9.04-8650-1_amd64.deb to see if it's improved?

[Guillermo Espertino (Gez) (gespertino-gmail)]

SCislaC: It isn't, unfortunately. The interpolation still looks awful

[Diederik van Lierop (mail-diedenrezi)]

This could very well be related to bug 168384 indeed. If it is I will have to kill myself ;-). The antialiasing for bitmaps is handled in exactly the routines that I was patching there.

Gez, you didn't accidentally change the antialiasing setting in the preferences? If that is not the case then we should revert that patch and hold it back until after the v0.47 release, it has caused too much trouble already.

Scislac, could you revert this patch please?

[Diederik van Lierop (mail-diedenrezi)]

I have not been able to reproduce this so far on my Fedora 10 x86_64 installation. I didn't see anything strange in the png files nor on the canvas. Gez, could you share your svg file and your preferences file with us?

[ScislaC (scislac)]

Gez, the patch which possibly created this has been reverted. When you can confirm this (as it seems likely), please close this report.

[Pablo Trabajos (pajarico)]

> You can use the same image I attached. It is easy to spot the problem during the scaling.
I think not. Both screenshot are already "processed" by Inkscape. I took a screenshot and did the test. On display I get a similar result when Ovrsample is set to none.

> Gez, you didn't accidentally change the antialiasing setting in the preferences?
I think this an important question, as having "none" there produces a similar result on display. I confirm that it affects exporting too.

[Guillermo Espertino (Gez) (gespertino-gmail)]

I didn't change the oversampling settings. It isn't related to the preferences file either, since I expliciltly removed the preferences file to try if it had something to do with that problem.
With 0.47 pre2, it works fine. I even can see the difference when I change the antialiasing values in the image.
With the newer builds it always display the images as if they would have oversampling set to none.

I'll try with a new build with Diederik's patch reverted.

Thank you for your feedback.

[Guillermo Espertino (Gez) (gespertino-gmail)]

Diederik: Please don't kill yourself... but it was your patch. :-p
Once it was reverted everything went back to normal.