Weighted Optimisation

Weighted Optimisation in Photoshop 6.0

There is a new feature in Photoshop 6.0: Weighted optimisation. This allows a single JPEG or GIF image to have variable compression . There is no special browser plug in required; and is reasonably easy to set up.

It is useful when there is a featured object, or text that must be of high quality, and the rest of the image is needed to be as small as possible.

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1. Create a selection around the object you wish to have in high quality. [878] images/01_createsel.jpg

2. Feather the selection, and Expand the Selection (Select>Feather and Select>Modify>Expand) [879] images/02_featherexpand.jpg

3. From the Channels palette, click on the “Create Channel from Selection” button[880] images/chanfromsel.gif Name the selection something useful. [881] images/03_channelopts.jpg

4. File>Save For Web. The button to click on to access the Modify Quality is the small circle. [882] images/weightopt.gif [883] images/04_jpegwopt.jpg

5. The black marker on the slider represents the black area in the chosen channel. Therefore, the black areas are getting a greater compression setting in the JPEG compression algorithm. The white end of the slider is having less compression. Areas in between get variable compression depending on the ‘greyness’ [884] images/05_weightoptset.jpg

6. With GIF images, there is no compression per se. Therefore, with GIF compression the Save for Web dialog box changes the lossiness of the GIF which reduces the resulting file size. [885] images/06_withgif.jpg