Sharpness of Image after multiple saves

[Guest]

When working with a jpeg in Paint, the more times it is saved and re-opened
more of the backround (white) of the drawing gets populated with colored
(mostly gray) pixels. Even after I clean them up (remove or change to white)
they reappear when saved and re-opened. These pixels show up on screen and
when printed.

Am I doing something wrong?

 

[Guest]

jpeg is a lossy format so if you keep saving and
reloading, you'll loose more and more. Use a non-lossy
format or don't reload so much. (This has nothing to do
with Windows by the way - it's just the nature of jpeg.)

 

[Crouton]

Save your picture as a .bmp file, this takes up more disk space but you can
load and save it as often as you wish. When you are satisfied that you no
longer wish to re-save it any more then save as a .jpg.
Jpegs achieve most of their compression by throwing away detail - not a
problem with just a few re-saves but the 'throwing away' process will
accumulate over multiple saves until it becomes visible. You'll notice that
the jpeg save options allow you to set the amount of compression - this is
basically asking how much can the compression throw away, the more it can
lose then the smaller the file size will become. If you really want to
continue saving as a jpg then alter the compression so that less is
discarded, that way you can do multiple re-saves.

 

[Al Smith]

Thanks for the help

:

The main thing to keep in mind is that some graphic formats are
"lossless" and some are "lossy" -- JPEGs are lossy. That means
that each time you save it, it loses more detail. You can save a
lossless graphic file a thousand times and not lose any detail. It
will still be as sharp as when you started. If you save a lossy
graphic too many times, you won't even be able to see what was in
the picture.

What you should do is this. When you want to work in a photo
editor on a JPEG (lossy format) you first convert it into a BMP or
other lossless format. Then you can fiddle with it to your heart's
content, and save it as many times as you wish, without degrading
the image quality (by the saves, at least). After you are all
finished fiddling, if you absolutely need to compress the image
file to save space, you can then convert it back to JPEG or some
other compressed graphic format. You are better off storing it in
the lossless format, however.