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RE: file size

  • Subject: [iris-photos] RE: file size
  • From: "Michael D. Greenfield" mgreenfield@cinci.rr.com
  • Date: Sun, 6 Nov 2005 22:58:29 -0500

There are 4 main techniques to control file size.
 
The first is cropping. This eliminates unneeded background. There is no effect on image quality
Any time you make changes on a jpeg you lose quality. Be it crop, resize or whatever.
 
The second is setting pixels (dots) per inch (dpi). As was  just pointed out, monitors show either 72 or 96. What is shown on the monitor when the dpi is 300 or 600 depends on the software being used. Some software shows the entire image at the monitor's dpi so the image is greater than the size of the monitor. This is usually hated by the person who received the image. Other software resizes the image so the image is just full screen. There can be image quality impacts of the resizing.
 
On the web 72 dpi is all that is needed. More will not show on the monitor only at the printer.
 
The third is image size. In general, image quality decreases as image size decreases.
 
Only for viewing, small image size makes it harder to see picture. If the dpi is large the information is there.
A 10 inch X10 inch  72 dpi photo is about as big as a 15"monitor can see without scrolling. It will be around 70 kb in size.
 
The fourth is compression. jpg is a compressed format. The jpg software can adjust the compression ratio. The greater the compression ratio the less accurate the color and detail. Considering the lack of color accuracy in the whole process of obtaining and viewing an image, compressing an iris image to a file size about 50K will be totally acceptable to most of this group. Anyone who needs greater quality can do so off line.
 
I have attached a photo of a Peter Jackson Louisiana iris seedling to show what is possible in terms of quality and size in a 63K file.
 
This is a good size for me. It is 6" X 6" on my 17" monitor.
 
Fortunately I have DSL and Windows XP so all of this discussion of file size has little significance to me.
Wondering if I sent you a dozen 12 meg Tiff's if you would take that back?  :-)
 
However I do remember the bad old days of dialup when I was quick to remind senders of large files to be more considerate in the future.
 
I be one and it was for sending to many photos to a photo list. They were under 50 kb.
Not that I didn't make mistakes sending before resizing.
 
Personally I think a restriction of 50K is too restrictive. When I was on a 44k dialup, I felt the file size limit should have been 300K. Any comments from the dialupers on what they feel is a reasonable limit. A change in the recommended file size may be a reasonable compromise.
 
Trouble is Harold there are people out there that have 56 k modems with a 28 k connections. Their phone lines are the problem not their computers. 44k connection is better than average. I believe a 75kb file would make a good limit.
 
I have cable.
 
Harold Peters
 
 
Mike Greenfield
Zone 5b
SW Ohio
Region 6
http://home.cinci.rr.com/irisinohio/


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