waifu2x doesn't handle transparency properly

[williammalo]

Examples:

Expected Result

Actual Result

To get the example image with good transparency, I ran waifu2x on the image over a black background and over a white background and compared the two with a filter. This proves that waifu2x does work properly if the background isn't semi-transparent

Original image:

[nodegin]

If I understand correctly you want to keep the edges crispy?
Why you not just resize it with PS / GIMP by Nearest Neighbor?

[williammalo]

@nodegin that would make the image pixellated :)

[Archeia]

This is also an issue for me as well. It was super fun converting old game assets that I had lost files over, but the sadness of making them transparent was :(

[Saren-Arterius]

I think waifu2x is not good at pixelated image scaling...
Maybe you would want to try 2xSAI?

[PwnicornDev]

I can confirm this, it doesn't have to do with pixellation in the original.
In the first example, the edges are blurred where they are flanked by transparent areas. In the second example I added a white background prior to upscaling, resulting in perfectly clean edges.

[internetakias]

Not sure if this is worth mentioning, but earlier versions of waifu2x-caffee could produce transparent images with sharp edges.

[PwnicornDev]

@internetakias Do you know an exact version where it was working? If we can find the commit that broke it, we should be able to solve it easily.

[internetakias]

@PwnicornDev
1.0.5 is the last version that produced scales with proper transparency.

[internetakias]

Hey @nagadomi. You haven't replied to this issue yet, so I want to ask you what you think of this and if there's a way to fix it.

[nagadomi]

The latest version slightly improves for this issue but still not enough.
I think this issue is difficult to solve in various cases. (semi transparent or fully transparent, for white background color or black background color)
Sorry, I am pending it.

[internetakias]

I understand. Thanks for replying and keep up the good work!

[nagadomi]

I fixed this issue. try http://waifu2x.udp.jp/

[andreili]

Sory, reopen issue...
Original image with alpha-channel:

Upscaled image (x2, without denoise):

Transparent space become opaque, which increased the size.
The game has a lot of images, and this problem increases its size by 50-60Gb = /

[nagadomi]

How is waifu2x supposed to do?
I think it is problem of an original image that has unreasonably large transparent area.

EDIT: I understood what you said. I will fix it soon.

[andreili]

Unfortunately, it is a feature of the original game, and such areas should be.
Under the program - it does not have to process the field with 100% transparency. Now she treats them as a whole, which significantly increases the processing time:

./images/./Event01/01-00/01-00-A01/01-00-A01-015.PNG: 2.3339378833771 sec
./images/./Event01/01-00/01-00-A01/01-00-A01-015SET.A.PNG: 4.6067349910736 sec
./images/./Event01/01-00/01-00-A01/01-00-A01-015SET.B.PNG: 4.6801130771637 sec
./images/./Event01/01-00/01-00-A01/01-00-A01-015SET.C.PNG: 4.6291019916534 sec

(The first - the background, the rest - imposed on the background image with transparency, similar to the above).

[nagadomi]

I fixed that file size problem.

before fix: 740888 bytes
after fix: 37333 bytes

And, if image has alpha channel, 2x process time is required. alpha channel upscaling with waifu2x improves the upscaling result in some case.
see: https://twitter.com/mhhpnvu/status/673488043735539712

[andreili]

Yes, the local version has updated and checked.
Thanks for the quick response.