Andreas Buchner <anbucx-> wrote:
>
>> Don't know how you downsampled, so I won't comment on sharpness...
>
> Used Photoshop to downsample bicubic. Do you have a recommandation
> how to improve quality?
As Bart van der Wolf has shown, the Lanczos filter (as in ImageMagick)
downsamples much better than Photoshop bicubic sharper. The bicubic
algorithm is perhaps more versatile than Lancsos, especially when changing
the ratio of x/y dimensions (aspect ratio). Here is the ImageMagic command
I use for 20% downsampling:
convert -filter Lanczos -scale 25% -unsharp 1x3+1+.09 in.bmp out.jpg
That results in quality 75 JPEG, which could be increased with the -quality
option. If you increase quality > 85, -sampling_factor 1x1 is recommended
for 4:4:4 chroma subsampling. Here is Bart's website:
http://www.xs4all.nl/~bvdwolf/main/f...e/example1.htm