vipsthumbnail - resize PNG without antialias

[mistermiracl]

I have an image, a triangle in this case, that is using just one color, meaning it doesn't have any pixels with alpha pixels except for the background that is fully transparent, I would like to keep it that way

og image

but when I resize the image using the following command:

vipsthumbnail triangle.png -s 500x -o triangle-tailored.png

antialias pixels are added to sharpen the edges Im guessing

is it possible to not do that using vipsthumbnail? thanks

[jcupitt]

Hi @mistermiracl,

No, vipthumbnail doesn't let you select the interpolator -- it tries to do this for you automatically..

You'll need to use one the language bindings (python, ruby, C++, php, rust, etc.) if you want more control over resizing.

[sergeevabc]

@jcupitt, is there any workaround for ordinary users, e.g. using vips instead of vipsthumbnail?

[jcupitt]

You can use resize instead, eg.:

$ vips resize triangle.png x.png 0.5 --kernel nearest

To make:

The 0.5 is the resize ratio, so shrink by x2 in this case.

[sergeevabc]

@jcupitt
If you are just interested in avoiding edge interpolation, then a block filter followed by nearest would be more accurate.

Which one is a block filter here?

$ vips resize
...
   kernel       - Resampling kernel, input VipsKernel
                        default enum: lanczos3
                        allowed enums: nearest, linear, cubic, mitchell, lanczos2, lanczos3
...

[sergeevabc]

Also, working with the resize command has the disadvantage that I rarely know the scale factor. But I know what width or height is desired. For example, the following is possible with ImageMagick: magick in.png -interpolate integer -filter point -resize 600x out.png

[jcupitt]

The block filter is a separate operation -- shrink -- due to the very different implementation.

You can compute scale factors for resize in bash with eg.:

width=$(vipsheader -f width $infile)
scale=$(echo $(echo "scale=10; $width / $target_size" | bc))

Though it's a bit ugly. Something like python is a lot simpler (obviously):

scale = image.width / target_size