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A reader recently wrote: "How do I reduce a 2-megabyte JPG photo to a few hundred kilobytes? I don't want to resize the picture; just make the file size smaller so it can be emailed as an attachment more easily."
Reducing a Digital Photo's File Size
Well, it's helpful to understand why digital photos are usually saved in the JPG format to begin with. There are file size choices that range from very small to very large (lower quality resolution to higher quality resolution). Surprisingly, going from a high bit count (hi-res) to a lower bit count (low-res) often results in an image that shows little discernable difference in quality.
By default, each time a JPG is saved (in many image-editing programs) it is compressed to a
file size of about 80 percent of the previous save. Well, an image thus compressed once
will usually not noticeably have the quality of its appearance diminished. However, additional 80%
saves can make a picture look very splotchy.
The original reason for compressing images was to accelerate their emailing speed and to conserve
disk space. However, in today's digital world of huge hard drives and high-speed internet service,
compressing a JPG is rarely helpful.
Also, once a picture has been compressed it can never be "uncompressed."
Therefore, you should give subsequent saves incremental name changes such as, say, Sunset-1.jpg,
Sunset-2.jpg, etc. Better yet, use Irfanview
(free image-editor from www.pcdon.com/irfanview)
which lets you choose your own JPG compression ratio, including the option of saving an image at
100 percent (i.e.: no compression at all).
Various image-editing programs have different ways of letting you adjust the bit count, but my favorite is Irfanview, which is a free download from Irfanview.com
Open a picture in Irfanview, go to File>Save As, and choose JPG from the "Save As Type" list. A sliding "Save Quality: (Best to Lowest) bar will appear that displays a percentage number as it is moved.
Experiment with different percentages to see how small you can make the file, yet maintain an acceptable image.
IMPORTANT: be sure to change the file name with each attempt (such as Mary1.jpg, Mary2.jpg, Mary3.jpg, etc.). Always retain a copy of the original image with its name unchanged. If the original's file size is reduced and then saved with the same name it can NOT be returned to its previous status.
This is why JPG is known as a "lossy" image format.
Before saving an image in IrfanView be sure "Show options dialog" (at the bottom of the page) is checked, whereupon "Save Quality" options will appear, displaying different compression ratios. (I normally use 100%.)