png alpha channel loss

[Kaens]

Hi,
I found a bug where the alpha channel is lost.
Using waifu2x-ncnn-vulkan-20210210-windows on an RTX 2070.
The command-line switch is just "-n -1" or "-n 0".

Before:

After:

[ghost]

The bit value of the image is strange. (It is marked as 8bit in Windows properties. It must be marked in 32bit.)
Use'-pix_fmt rgba' in ffmpeg or save it through a separate image editing program.

[CounterContradiction]

@Kafu-Yukimura is right.

I have a similar image where it showed that it is 8bit if viewed through Windows Properties(Right Click-> Properties), and it also losses its transparency when using waifu2x-vulkan.

I saved your image as bear.png and run it through ffmpeg with the suggested command:
.\ffmpeg.exe -i .\bear.png -pix_fmt rgba bear_ff.png
And bear_ff.png ran without losing its transparency (-s 2 -n 2):

An altenative I found is with python and the Pillow library:

from PIL import Image
img = Image.open("bear.png")

#Checks if img is 8bit
if img.mode == "L" or img.mode == "P":
    #Converts to 32 bit and overwrites the original image. 
    #Use a different filename from the original if you want to preserve the original image.
    img.convert("RGBA").save("bear.png")  

[nihui]

fixed in 7ab564a