bruns added a comment.
I think the following yields quite good results:
qreal distance(int width, int height, int desiredWidth, int desiredHeight)
{
auto targetSamples = desiredWidth * desiredHeight;
auto xscale = (1.0 * desiredWidth) / width;
auto yscale = (1.0 * desiredHeight) / height;
// clamp to the lower of the two scales
// also clamp to one, as scaling up adds no effective
// samples, only interpolated samples
auto sampleScale = min(1, min(xscale, yscale));
// number of effective source samles in the target
auto effectiveSamples = width * height * scale * scale;
// scale down another time, to account for loss of fidelity when
// using a downscaled image, biases towards smaller downscaling ratios
effectiveSamples *= scale;
return targetSamples - effectiveSamples;
}
REPOSITORY
R320 KIO Extras
REVISION DETAIL
https://phabricator.kde.org/D14308
To: broulik, #frameworks, dfaure, ngraham, pali, vonreth, antlarr
Cc: anthonyfieroni, bruns
