Thumbnail Primer

by harvey cohen

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.
Classic Lena Image
256x256x8 bit grayscale

4x4 block mean thumb
exploded to full-scale below

Lena - again

Thumb based on TLHC of 4x4 block exploded below

Thumb based on
"colour-mean" on 4x4 blocks.

Thumb based on TLHC of 4x4 blocks.

Clown 320x200x8 bits colour

Clown thumbnail image based o
"colour-mean" on 4x4 blocks.
Exploded to right

Clown thumbnail image based on top left hand corner (TLHC) pixel of 4x4 blocks.
To right the exploded TLHC thumb.

Thumbnails of Mandril 512x512x8-bit Colour Image

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.

To see the FF mandril image, with these four 64x64 thumbnails alongside, click on

Difficult Thumbs

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

Fluctuating Thumbs

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
See also
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
See also my papers concerning thumbnails and thumbnail-based image coding, including thumbnail-based fractal coding, in the author's download centre
Harvey A. Cohen, Thumbnail-based Image Coding Utilising the Fractal Transform Proc.IEEE Int'l Conf Image Processing ICIP'96, Lausanne, Switzerland, Sept 16-19, 1996. Vol 1, pp 105-148 This papers is listed as Paper 96:5 at the author's download centre
Harvey A. Cohen, Access and Retrieval from Image Databases Using Image Thumbnails, Proc. Int'l Conf Signal Processing Applications, ISSPA, Gold Coast, August 26-28, 1996, Vol 1, pp 427-8 This papers is listed as Paper 96:6 at the author's download centre

harvey cohen's home page