Why is VIPS downsampling so good?

[CAcreeks]

lol; yes read. Also, you will need to crop out the reduced size result (I didn't create the preset; just occasionally use it. ).

When trying to run the decimation script, I get this error for floor and ceiling:

attempt to index global 'math' (a nil value)

Do I need an include or load statement? The math functions might be in GEGL, which is present. Help appreciated.

 

[CAcreeks]

attempt to index global 'math' (a nil value)

This appears to be a problem with the Ubuntu build or their integration of gluas libraries with GIMP.

https://bugs.launchpad.net/ubuntu/+source/gluas/+bug/1164421

I will try it in GIMP for Windows.

 

[CAcreeks]

My theory is that vipsthumbnail is so good at downsampling (as good as Photoshop bicubic with Smart Sharpen) because it uses the same sharpening method: deconvolution. From source code:

else if ( strcmp (convolution_mask, "mild" ) == 0 ) {
mask = vips_image_new_matrixv( 3, 3,
-1.0, -1.0, -1.0,
-1.0, 32.0, -1.0,
-1.0, -1.0, -1.0 );
vips_image_set_double( mask, "scale", 24 );
}