Scanning docs

[KA4HJH]

>PDF is great for documents that are composed like a book (chapted
>headings, page numbers, etc.) and are likely to be printed out in
>pages, but otherwise it's a drag.

PDF is a multi-page format so it's great for multi-page documents. It 
uses several different compression schemes for different kinds of 
images, which you can mix in the same document. It's more work to get 
right.


>JPEG is for photographs, paintings, and stuff that's of similiar
>content with lots of color shading.

Continuous tone images, like photos.


>GIF encodes colors with a lookup table, so it's great for drawings,
>schematics or logos.  GIF format can also assign a transparent color
>for doing non-rectangular images.

GIF is better for images with solid blocks of color/grays, like drawings.


>BMP is Microsoft specific and not appropriate for the web.
>
>TIFF is for some specialized printers and not appropriate for the web.

TIFF is mainly used as a pre-press format. Lossless compression is 
optional. The files therefore are pretty big. Useless for web 
publishing.


>Before you place the images on the web, do what you can to reduce the
>file size.  JPEGs can be often created with less resolution and the
>grainyness might not be a problem.  GIFs can often be created with
>a smaller color lookup table.

Note that reducing the number of colors will not help a JPEG--it may 
actually make the file bigger.


>So the answer is likely to be to use GIF format with maybe 4 levels of
>gray.

Sometimes GIF's are smaller, sometimes JPEG's are. When in doubt, 
save as both and see. It doesn't hurt to test.

If you're just scanning docs, schematics, etc., don't save them as 
progressive images. That way people (like me) can be looking at a 
schematic while it's loading.


Not mentioned: OCR (optical character recognition). Turns the scan 
back into pure text, which of course takes up a LOT less space. Only 
problem: very time consuming. VERY time consuming, especially with 
technical writing. I've done it, and it looks fabulous, but I have 
better things to do with my time.

Here are some examples (recreations of the original articles):

http://www.crowncity.net/ratcave/Electro/Electro.html

But don't let me stop you.



-- 
Terry Bowman, KA4HJH
"The Mac Doctor"