Re[2]: scanned images

Subject: Re[2]: scanned images
From: "Arlen P. Walker" <Arlen -dot- P -dot- Walker -at- JCI -dot- COM>
Date: Mon, 19 Dec 1994 09:51:00 -0500

Also, if you have access to an application called Adobe
Photoshop it will allow you to change the color (usually RGB) scans
from full to something called indexed color. This one switch has
sometimes halved my image file sizes.

I would hope it would do more than halve it. RGB uses 4 bytes per pixel of color
information (typically one byte each red, green, blue information along with one
byte called "alpha channel" information). This system absolutely identifies each
color to be used in the image. "Indexed" color uses one byte to identify the
slot in a palette of x (x is variable but limited to 256 or less) where the
color is identified. Since the overhaed of the palette identification (the
palette must of course hold the absolute identification of each color in it) is
involved, you won't get the full 4:1 reduction, but you should get close to it.

JPEG (Joint Photographic Experts Group) is a releatively new standard for image
compression which works astoundingly well. It can achieve 10:1 or better
compression of images. Be advised this is a "lossy" compression scheme. (It
removes detail in areas of the image where it judges detail to not be important.
Yes, that's right, it irrevocably throws away some of the image it compresses.
Before you scream, try it on a few images. I've loaded several "before & after"
images into Photoshop, and I've rarely been able to spot the "lost" detail. And
even then it wasn't important.)

Have fun,
Chief Managing Director In Charge, Department of Redundancy Department

Arlen -dot- P -dot- Walker -at- JCI -dot- Com
In God we trust; all others must provide data.

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