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Photoshop in Focus

JPEG is an important file format when you consider the number of such images on the Internet and those taken with digital cameras. The lossy compression algorithm that JPEG uses is worth exploring:

1.
Open an image in Photoshop, any image.

2.
Use the menu command File, Save As, and select JPEG as the file format.

3.
Use an image quality value of zero and save the file to your desktop.

4.
Close the open file and use the menu command File, Open to open the file you just saved.

5.
Click the leftmost button at the bottom of the History palette to create a copy of the open image.

6.
Save this copy, appending “-1” to the name. Again, use JPEG quality 0. Close and reopen the –1 file.

7.
Position the two windows next to each other and zoom in to 500% on an area of detail. Compare the two. Although neither looks good, they should be nearly identical.

8.
Use the menu command Image, Canvas Size. Click in the lower-right corner of the proxy (the 3×3 grid labeled Anchor). Switch the unit of measure to Pixels, and input a height and width, each 4 pixels smaller than the original value. Click OK.

9.
Save the file as JPEG again, using the lowest quality setting.

10.
Close and reopen the image.

11.
Zoom in to 500% and compare this version to the original.


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