TOW - Digital Photography of Plants and subsequent manipulation of images for printing, the web etc.

John Lonsdale
Mon, 16 Dec 2002 17:54:36 PST

Yes,  the pixels refer to the pixels dimensions of the image, e.g. 640 x
480, 1600 x 1200 etc.  With most cameras you can select from multiple pixel
dimensions for the capture of your original images.  For example I use 2048
x 1536, to gibe me 3.4 megapixels, or so.

The pixel dimensions have nothing to do with compression.  The latter is a
way of driving down the file size (and quality) whilst maintaining the pixel
dimensions.  Thus I can save my original 2048 x 1536 image with whatever
compression I want in the jpg format, to end up with a variety of file sizes
proportional to the compression.  You can also independently change both the
resolution (in pixels per inch or dots per inch, dpi) and the pixel
dimensions of an image, for example to get an original down to the 640 x 480
format I use for web work with a resolution of 72 dpi.  In this case PS
resamples the pixels and cuts out a number to bring the dimensions down to
the value I've chosen.  Compression, pixel dimensions and resolution are
completely different things but in combination determine the quality and
file size of your final image.  In going from the camera to the web I reduce
both the file size by compression and the pixel dimensions by resizing.  A
jpg is just a file format made by lossy compression - it can be as much or
as little compressed as you choose, depending upon your needs.


PS. And how about comments from someone other than me - PLEASE !

Dr John T Lonsdale
407 Edgewood Drive,
Exton, Pennsylvania 19341,  USA

Phone: 610 594 9232
Fax: 801 327 1266

Visit "Edgewood" - The Lonsdale Garden at

Zone 6b

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