Everyone on the Web uses Image thumbnails to provide a click on link to FF images, such as a full fledged (= full-sized) image of the writer but just what IS a good thumbnail ? How should the few pixels in an image thumbnail be related to those in the FF image ? Here are some ideas.
This is the thumbnail of an excellent image of the US flag. It's lousy -- but why?
The reason lies in the algorithm used.
Thumb based on
"colour-mean" on 4x4 blocks.
Thumb based on TLHC of 4x4 blocks.
Clown 320x200x8 bits colour
Thumb based on 8x8 mean colour index. Guess who's coming to dinner ?
Thumb based on top left corner pixel of 8x8 block. Chunky but good colour
Thumb based on randomly chosen pixel in 8x8 block. Very chunky
Thumb based on (my) colour mean per each 8x8 block. In soft focus. No irritating artifacts.
There is no golden rule that (colour-) mean thumb is better that Top Left Hand Corner (TLHC) pixel thumb or vice versa: here are two conflicting examples: Lena dithered (Floyd-Sternberg with threshold = 200) and Clown subject to about 70% shot (Poisson) noise.
Mean >> TLHC . . . . . Mean << TLHC . . . . Thumb Quality Comparison
What happens if thumb simplified by use of JPEG
Good Thumb JPEG form Click for exploded versions of each thumbnail image
Thumbnail Utilities Software
QPV (formerly QPEG and QPEG386) - a Shareware Windows program -- for DOS/Windows offers a large directory -- which is annotated with image size and colour details -- while displaying a Thumbnail (gray-scale only) of the currently highlighted directory entry
Graphic Utilities' Site & Version FAQ v.022
That's all folks -- but wait a while -- someday there will be more !!!
Link to thumb fractal web page