When I reduce 300-dpi jpegs to 100 dpi (size: 447 pixels horizontal, 350 vertical) for posting on the Web or e-mailing, the image, which originally had smooth edges, now has jagged and conspicuously bit-mapped edges. (But, curiously, not always--sometimes the 100 dpi image looks as smooth as the 300 dpi one.) There must be a step that I'm omitting--what would this be? Thanks,
You might consider changing the resampling algorithm in the Image Size dialog box.
Choose Image > Image Size...
Select the Resample option if it is not selected already.
Select Bicubic from the Resample dropdown.
Change the image dimensions to suit your needs.
Bicubic is the best (most accurate) interpolation method for image re-sizing images. It sounds like another is selected. Bicubic Sharper is good for reducing images but it can lead to "jaggy" edges. The Nearest Neighbor method will produce even worse results. Click below to learn more.
Here's a good trick-
When saving JPEG images for delivery on the Web, a slight blur can help reduce the overall file size. Selectively blurring the edges that are jagged might help solve two problems.