Alpha scaling seems to behave weirdly #24

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NRK · 2024-06-20T00:56:49-07:00

NRK commented

2024-06-20 00:56:49 -07:00

To reproduce, ~~open the attached image~~ (I can't seem to attach pam files, so just posted the cli commands to recreate the image instead) with nsxiv -z 800 {img.pam} and notice that there's a red outline at the top, even though the red pixels have an alpha of 0.

$ cat > /tmp/pam.pam << EOF
P7
WIDTH 8
HEIGHT 2
DEPTH 4
MAXVAL 255
TUPLTYPE RGB_ALPHA
ENDHDR
EOF
$ for ((i=0; i<8;++i)); do printf "\xFF\x00\x00\x00" >> /tmp/pam.pam; done
$ for ((i=0; i<8;++i)); do printf "\x00\xFF\x00\xFF" >> /tmp/pam.pam; done
$ nsxiv -z 800 /tmp/pam.pam

To reproduce, ~~open the attached image~~ (I can't seem to attach `pam` files, so just posted the cli commands to recreate the image instead) with `nsxiv -z 800 {img.pam}` and notice that there's a red outline at the top, even though the red pixels have an alpha of 0. ```console $ cat > /tmp/pam.pam << EOF P7 WIDTH 8 HEIGHT 2 DEPTH 4 MAXVAL 255 TUPLTYPE RGB_ALPHA ENDHDR EOF $ for ((i=0; i<8;++i)); do printf "\xFF\x00\x00\x00" >> /tmp/pam.pam; done $ for ((i=0; i<8;++i)); do printf "\x00\xFF\x00\xFF" >> /tmp/pam.pam; done $ nsxiv -z 800 /tmp/pam.pam ```

NRK commented

2024-06-20 01:02:54 -07:00

Actually, the problem seems like it's coming from anti-aliasing, not scaling. If I toggle anti-aliasing with a then the redish blur goes away.

Actually, the problem seems like it's coming from anti-aliasing, not scaling. If I toggle anti-aliasing with <kbd>a</kbd> then the redish blur goes away.

kw commented

2024-06-21 07:12:27 -07:00

Hmm.. I'm not quite sure precisely what to expect, but the behavior seems fine to me.

NRK commented

2024-06-21 23:02:32 -07:00

I would expect the red color not to show up since it has an alpha of 0. I attached a png version of the test image. If I open it in firefox or mpv, there's no red anywhere.

test.png

96 B

kw commented

2024-06-22 00:03:13 -07:00

I wonder if we are seeing the same thing.
I have attached screenshots of
$ nsxiv -z 800 pam.pam
and
$ imlib2_view -s 200 pam.pam
nsxiv and imlib2 both from current master.

The nxsiv image is rather small, and I find it hard to see much detail (or red blur).
The imlib2 image seems good to me. I see no reddish blur (but I do have minor problems with dark reddish nuances :) )

Could this be about which background the (transparent) scaled image is blended onto?
I tried changing imlib2_view's usual checkerboard background to pure white, and I still don't think I get reddish blur.

I wonder if we are seeing the same thing. I have attached screenshots of $ nsxiv -z 800 pam.pam and $ imlib2_view -s 200 pam.pam nsxiv and imlib2 both from current master. The nxsiv image is rather small, and I find it hard to see much detail (or red blur). The imlib2 image seems good to me. I see no reddish blur (but I do have minor problems with dark reddish nuances :) ) Could this be about which background the (transparent) scaled image is blended onto? I tried changing imlib2_view's usual checkerboard background to pure white, and I still don't think I get reddish blur.

imlib2_view.png

3.1 KiB

nsxiv.png

4.1 KiB

NRK commented

2024-06-22 01:05:40 -07:00

On my end, this is what I'm seeing with nsxiv -z 1600 (I increased the zoom limit in config.h):

With imlib2_view -s 200 I see this, which looks about right:

I suppose it could be an issue with nsxiv. I'll investigate this further and report back.

On my end, this is what I'm seeing with `nsxiv -z 1600` (I increased the zoom limit in `config.h`): ![image](/attachments/28e1c586-d9f0-43c0-913a-4696c939bf00) With `imlib2_view -s 200` I see this, which looks about right: ![image](/attachments/3ca0ae15-ee19-4b1c-8c2a-0ca5abeef9af) I suppose it could be an issue with nsxiv. I'll investigate this further and report back.

image.png

312 B

image.png

2.0 KiB

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Reference: old/legacy-imlib2#24