A test page for the new VIPS image scaler is now available: https://test2.wikipedia.org/wiki/Special:VipsTest You can give it names of images from Commons and it will show a comparison with a moving divider, with the thumbnail from ImageMagick on the left, and the one from VIPS on the right. I'll explain what you would expect to see when using this tool: For JPEG images, using a sharpening radius of 0.8 will make the VIPS result roughly match the ImageMagick result, as long as the thumbnail is reduced to less than 85% of the original width. With not enough sharpening, the resulting image looks blurry. With too much sharpening, contrast in fine detail will be unrealistically enhanced and high-contrast borders will develop "halos". Above about 50% reduction factor, the block average introduces artifacts in fine detail, so enabling the "bilinear" option will look better, and will more closely match ImageMagick. But if the bilinear option is used with a reduction factor much smaller than that, severe artifacts will be seen in areas of contrasting fine detail. At small reduction factors, the main difference between ImageMagick and VIPS is that VIPS uses a simple block average whereas ImageMagick uses a more complex windowing function. This leads to minor differences in fine detail. What we're looking for out of this test is: * Confirmation that VIPS is not completely failing fpr some class of images. * Suggestions for parameter values (sharpening, bilinear) for various source and destination sizes. VipsScaler allows these parameters to be configured depending on source size and reduction factor. -- Tim Starling