[sdiy] OK, one of you computer geeks, explain this..

[James R. Coplin]

It would depend on the format used for the colorspace.  A bmp format is raw
and even if it is grey scale but the color space is specified as 24bit, each
pixel will be 24 bits even if they only store the 8 bits of data that make
up greyscale.  If you were to convert the greyscale to zillions of colors
via 24bit jpg, then the color space compression will give you the gains.

All of this is dependent on the application you are using for the scanning,
how the pdf translator deals with the info, etc.  

James R. Coplin
***************
If anyone asks of my whereabouts,
simply tell them i've gone out the window
for a spot of tea and am not
expected back any time soon.
***************

> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl [mailto:owner-synth-
> diy at dropmix.xs4all.nl] On Behalf Of J. Larry Hendry
> Sent: Sunday, January 30, 2005 5:37 PM
> To: Synth-DIY
> Subject: [sdiy] OK, one of you computer geeks, explain this..
> 
> While this pertains to scanning and file structure, it is not off topic
> because I am scanning synth schematics.  Due to the black and white
> scanning
> I have done in the past, I pretty much understand how to minimize PDF file
> size for a given resolution (through the BMP file).  However, I am now
> working on documents that require color and grayscale. While some of the
> document is color, about 2/3 is grayscale.  So, I thought I would save
> file
> size by scanning those in gray instead of color.
> 
> Here is what puzzles me. Let me throw some file sizes out there for one of
> my large 11x17 pages to see if any of this makes sense.
> 
> This page was scanned (paste a few together) in grayscale as a bitmap and
> results in 13.2 MB file size.  I normally scan everything to Bitmap and
> then
> convert to PDF as that has always given me the most efficient file size
> (past B&W experience).  So, I convert the file to a PDF and the resulting
> file is about 2.6 MB.  Well, I was hoping for better, but I thought that
> was
> it.  Then, I started noticing some of the color pages were smaller once
> converted to PDF.  I wondered why since the color BMP files were so much
> larger.  So, as an experiment, I took my 13.2 MB grayscale page and
> converted it to full 16 million colors file in my photo editor.  As
> expected, the file size jumper up to 39.7 MB.  I'm still understanding OK
> up
> to here.  But, now I take that color file and convert it to PDF.  The
> resulting file is only 1.15 MB.
> 
> So in summary,
> gray file started 13.2 MB bitmap
> converted to PDF @ 2.6 MB
> 
> same gray file to full color = 39.7 MB
> converted that color file to PDF @ 1.15 MB
> 
> Of course, since the original source file was grayscale, even the color
> PDF
> looks grayscale.  In fact I cannot tell the two images apart.  However,
> the
> one that was converted to the very large color file first ended up the
> MUCH
> smaller file size when converted to PDF.
> 
> If any of you who are considerable more geeked than I concerning computers
> can 'splain this to me and Lucy, that would be great.  Maybe I will learn
> something that will help me additionally control the file size on these
> large, highly detailed scans.
> 
> Larry Hendry
> computer geek NOT.
> :-)
> 
>