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[aprssig] APRS presentations

Stephen H. Smith wa8lmf2 at aol.com
Wed Oct 8 19:02:53 UTC 2008


Bruce Coates wrote:
> Hi Brian
>
> PowerPoint will do this for you.  Simply right click on any image, select 
> Properties, then Compress.  This will apply this setting to all images in 
> that document.
>
> 73, Bruce
> VE5BNC
>
>
>   


This DOES NOT reduce the number of pixels in the image.   It only 
attempts to more efficiently encode and store a needlessly high number 
of pixels in the original image.   

The chronic problem is the mindless "Megapixel Horsepower Race" in 
digital cameras and the marketing hype to the technically-illiterate 
public surrounding them.  

Current digicam images contain three, four, five times as many pixels 
(or more) than can be displayed on most electronic devices.    Consider 
that a 1024x768 pixel "XGA" display is "only"  3/4 megapixel .  A 
1600x1200 "SXGA" display is only 1.9 megapixels.   Even a full HDTV 
1080i image (1920x1080) is only 2.07 megapixels.  And that assumes the 
picture is in the 16:9 aspect ratio wide-screen format.   Displaying an 
undistorted "normal" 3:4 ratio camera snapshot on an HDTV (i.e. with 
reverse "letterbox" black areas on the left and right sides) would yield 
a 1440x1080 (1.5 megapixel) image.

[I  gag and/or sneer when I watch the megapixel-mad clueless public 
display their "5-megapixel" photos on 7" digital picture frames. AT 
LEAST* 90%* of the pixels in the original image are being discarded 
before the picture reaches the 640x480 (1/3rd megapixel) VGA display!]

The only place where the 5-plus-megapixel resolution of current digicam 
images can possibly make a difference is either:

o    if you very aggressively crop the original images (i.e. use only a 
tiny portion of the original photo) 

o    Print to paper.   (Assuming a typical inkjet printer with an 
effective resolution of 300 DPI and a letter-sized printout with a 
quarter-inch margin all around:     (8" x 300) x (10.5" x300) =  7.56 
megapixels   I.e. the effective resolution of ink on paper is far far 
higher than even high-end electronic displays. )



The megapixel overkill issue becomes even more absurd in public 
presentations, since most  of the computer video projectors commonly 
used only produce 800x600 pixel ( less than half a megapixel) SVGA  or 
1024x768 (3/4 megapixel) XGA  images.  And that assumes the image is  
displayed FULL SCREEN with no Windows widgets, scroll-bars, white space, 
borders etc.   

[I have been repeatedly frustrated when I have asked for mere 1024x768 
res projectors at ham club meetings, for map displays during APRS demos, 
only to be provided with crappy 600x800 units.]

The bottom line is that the current megapixel mania yields grotesquely 
large files if these large images are mindlessly inserted as-is into 
Powerpoint presentations, web pages,  or other electronic image 
applications.   These absurdly large images need to be down-sampled 
(reduced in resolution) 50-75% or more, *BEFORE* they are inserted into 
Powerpoint, web pages, etc, and then re-compressed for further size 
reduction.






--

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com  --OR--   http://wa8lmf.net

World Digipeater Map
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JavAPRS Filter Port 14580 Guide
  http://wa8lmf.net/aprs/JAVaprsFilters.htm

"APRS 101"  Explanation of APRS Path Selection & Digipeating
  http://wa8lmf.net/DigiPaths

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