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Old 08-28-2003, 09:14 PM
nmess's Avatar
nmess nmess is offline
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Join Date: May 2003
Posts: 421
Default jpeg compression

I've noticed that some of the photos being posted suffer from over compression. This produces noise, artifacts and jaggies which all serve to degrade image quality. Most of the photo editing tools give you the option of choosing the level of compression to optimize the file size. TE allows file sizes up to 200,000 bytes (200KB).

I'm not aquainted with PS and some of the other packages and will let someone experienced with them address this if they wish. I'll just look at PSP since that is what I currently use.

When you're finished editing the image, choose file/save as. When the dialogue box appears, choose options. Another dialogue box will appear, choose run optimizer. Here you will have the ability to choose the compression setting and the optimizer will tell you the resulting file size. To maintain as much detail without the noise, artifacts, etc. Choose the compression level that will produce a file just under 200,000 bytes.

Though most folks here know, I'll mention it anyway for any newbies. When editing an image, saving the image as a jpeg automatically compresses the data in the file. This happens each time you save the file. Each time some of the data is discarded (degrading the image quality a bit). So to minimize this, try to make all of your adjustments in one session if possible, and save the finished work under a new filename (to preserve the original). If it will be neccesary to do your work in multiple sessions, it is my suggestion that you choose an uncompressed format (tiffs and bitmaps are uncomressed) until you're ready to prepare your posting file.

I hope this helps, and perhaps others can address other packages such as Photo Shop or Photo Paint and such.
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Old 08-28-2003, 09:22 PM
AdrianW's Avatar
AdrianW AdrianW is offline
Join Date: Mar 2003
Posts: 1,596
Default Re: jpeg compression and Photoshop

Quick workflow:
1) Make all alterations to the image
2) Resize to the final image dimensions using Bicubic interpolation
3) Sharpen at 75% (I use Sharpen, then fade it to 75% but you could use USM)
4) SaveForWeb, start with a quality of 60 or so, and reduce it until artifacts appear. Try turning Progressive on and off as that might save a couple of kb.
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