Trials

[Bart_van_der_Wolf]

Originally Posted by Nicolas Claris

If for ages upsampling has been crucial for many of us wishing to get giant prints, I'm now also facing with downsampling (mainly for the web and low resolution slideshow for client's selection)!
Reducing with good quality a 7264 x 5440 pixels file to 800 x 599 pixels seems a real challenge…
Any hints?

Hi Nicolas,

I'm not too familiar with software for the Mac platform, but I believe you also have a Windows machine used by one of your employees for Web related stuff. In that case there is a nice (free) application that does a nice job, called RIOT. One of the useful features is that image parameters can be tweaked for quality (e.g. the JPEG subsampling of color in addition to the overall compression/quality setting), but also for size in bytes (for webpages that load faster or consume less bandwidth on mobile devices. It offers several downsampling filters that can reduce some of the issues that accompany downsampling, e.g. moiré and jaggies.

Unfortunately, it is not perfect. For one, it is missing one parameter that improves images in a sometimes subtle (and sometimes in a dramatic) way, gamma control. When the resampling is not executed at gamma 1.0 then there may be issues such as described at:
http://www.4p8.com/eric.brasseur/gamma.html . One retains more sparkling highlights when the gamma is reduced to linear gamma for the downsampling interpolation itself.

The only application (a set of commandline utilities) I know of that allows full control, is Imagemagick. One can make a script to easily execute the right steps for a given task, and e.g. in Windows create a batch file where images can be dragged and dropped on to produce the required output.

Cheers,
Bart