[Coco] Initial Tests and Results

Michael Wayne Harwood michael at musicheadproductions.org
Sat Jun 11 13:06:26 EDT 2005

I have been gathering data to use in determining what standards should be
set for several aspects of the Rainbow on Disc project.  There are two
distinct aspects I was seeking to gather data for: 1) appropriate
standards for the orginal scans of the magazines, and 2) end product post
production issues.  This email is meant to be a quick summary of the work
done so far - I apologize for the somewhat haphazzard way this is
presented - this information is provided as a starting point for

Files on the Web

I have placed several .pdf files on my website for reference.  The largest
of them is 2.8mb in size, but please bear in mind that my web server is on
the other end of a consumer DSL connection.  My uplink is rated for a
maximum speed of 384kbps, so if multiple people are downloading things it
may be a bit slow.  The following is a list of the files that are
pertinent to this post:

A summary of file sizes.

PDF files that summarize the tests.  150ppi.pdf, 200ppi.pdf, and
300ppi.pdf all have three pages each - the first page is a scan at 1bit
black and white, the second page is a 24bit color scan, and the third page
is the result of post processing (see the section below regarding this). 
The grfx_all.pdf file is to show the results of what a scan of a page with
full color graphics would look like at different scan resolutions. 
grfx_all.pdf has three pages - page 1 is a 150ppi scan, page 2 is a 200ppi
scan, and page three is a 300ppi scan.

File Sizes

If you look over the grfx_all.txt file you can see a summary of the file
sizes I came up with throughout all of the steps.  I feel the results
documented are fairly self explanatory, but if for some reason I have left
out information that would make things clearer please let me know.

Post Processing

To get the result from page 3 of the example .pdf files (300ppi.pdf, etc)
I used two scans of the same page (24bit color and 1bit B&W) so that I
could use the 1bit black and white scan to create a mask applied to the
24bit color scan so that only the color information I wanted to show would
come through.  The end product looks quite a bit cleaner that the orginal
24bit color scan, though there is a little loss in graphic quality.

Here are the steps I used:
1. Load the 24bit color scan into the Gimp
2. Load the 1bit B&W scan as a second layer on top of the color layer 3.
Use the "Select a color" tool to select all the black areas in the B&W
4. Clear all of the selected black areas in the B&W layer to make these
areas transparent - the bottom color layer should now show through the
areas cleared.
5. Merge the layers
6. Save the result

Michael Harwood
/Any spelling errors are intenshunal/

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