Most scaling algorithms remove alpha channel when resizing an image

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damian101
Posts: 12
Joined: Fri Dec 22, 2017 12:43 am

Most scaling algorithms remove alpha channel when resizing an image

Post by damian101 »

With scaling methods Hermite, Gaussian, Bell, BSpline, Mitchell, Lanczos and Hanning the alpha channel gets removed when resizing an image.
Only Nearest Neighbor and Bilinear work as expected and preserve the alpha channel.
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xnview
Author of XnView
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Joined: Mon Oct 13, 2003 7:31 am
Location: France

Re: Most scaling algorithms remove alpha channel when resizing an image

Post by xnview »

i can't reproduce, could you send me a sample image?
Pierre.
damian101
Posts: 12
Joined: Fri Dec 22, 2017 12:43 am

Re: Most scaling algorithms remove alpha channel when resizing an image

Post by damian101 »

xnview wrote: Thu Jan 14, 2021 8:43 am i can't reproduce, could you send me a sample image?
Yes, I also could not reproduce this issue until I found the image I originally had the problem with. It's just 17x17 pixels in size, but it's not the size that causes this, since the issue can not be reproduced after reencoding the image with XnConvert.
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xnview
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Re: Most scaling algorithms remove alpha channel when resizing an image

Post by xnview »

I can't reproduce with the file, could you post a screenshot of resize dialog?
Pierre.
damian101
Posts: 12
Joined: Fri Dec 22, 2017 12:43 am

Re: Most scaling algorithms remove alpha channel when resizing an image

Post by damian101 »

xnview wrote: Mon Jun 14, 2021 8:27 am I can't reproduce with the file, could you post a screenshot of resize dialog?
Can't reproduce either now. I'm on Arch Linux, no idea why it did not work a few months back. Everything's working fine now. :)