Wesley R. Elsberry
Posts: 4991
Joined: May 2002
|
To get the most apparent sharpness after downsizing, apply a touch of "unsharp mask" at the new smaller size. I look for the amount that does the most sharpening while adding just a smidge of edge contrast. If you do too much you will see artifacts where objects will have obvious changes in color/brightness in the adjacent background. It usually takes a bit of experimentation to find the right parameters. GIMP does a perfectly good job on this. Choose the "Sinc (Lanczos)" filter option when rescaling, then you can tap the "Preview" checkbox on and off in the "Unsharp Mask" filter to see what the current parameters do for you.
For serious upscaling, I use a Windows application called QImage from DDISoftware. It has a number of advanced filtering algorithms to handle upsizing a photo to avoid the jaggies and make it as natural-looking as possible.
To get the most out of JPEG for the web, get "jpegoptim". This will allow you to strip out the EXIF data and set a JPEG quality factor.
I do a lot with scripts at the command line. Currently I have two scripts in Perl, one to resize photos so I have thumbnails, a 560-pixel wide/tall version, and a 1024-pixel wide/tall version. Perl calls "jhead" to automatically rotate the images taken with my Nikon DSLR, then ImageMagick routines to handle the rescaling, normalization, and unsharp mask operations, and "jpegoptim" to strip EXIF from the new sizes. The other script creates HTML galleries so that I can upload entire directories of images to my server. I am looking to redo the scripts in Python as I get a chance, but that may be a while down the road.
--------------
"You can't teach an old dogma new tricks." - Dorothy Parker
|
