User Guide

244 Chapter 12: Optimizing and Exporting
Selectively compressing areas of a JPEG
Selective JPEG compression lets you compress different areas of a JPEG at different levels. Areas
of particular interest in an image can be compressed at a higher quality level. Areas of lesser
significance, such as backgrounds, can be compressed at a lower quality level, reducing the overall
size of the image while retaining the quality of the more important areas.
The selected area in this image is being compressed at a quality level of 90, while the unselected area is
being compressed at a quality level of 50.
To compress selected areas of a JPEG:
1 In Original view, select an area of the graphic for compression using one of the Marquee tools.
2 Choose Modify > Selective JPEG > Save Selection as JPEG Mask.
3 Choose JPEG from the Export File Format pop-up menu in the Optimize panel, if it’s not
already selected.
4 Click the Edit Selective Quality Options button in the Optimize panel.
The Selective JPEG Settings dialog box opens.
5 Choose Enable Selective Quality and enter a value in the text box.
Entering a low value compresses the Selective JPEG area more than the rest of the image.
Entering a high value compresses the Selective JPEG area less than the rest of the image.
6 Change the Overlay Color for the Selective JPEG area if desired. This does not affect
the output.
7 Select Preserve Text Quality. All text items will automatically be exported at a higher level,
regardless of the Selective Quality value.
8 Select Preserve Button Quality. All button symbols will automatically be exported at a
higher level.
9 Click OK.
To modify the selective JPEG compression area:
1 Choose Modify > Selective JPEG > Restore JPEG Mask as Selection.
The selection is highlighted.
2 Use the Marquee tool or another selection tool to make changes to the size of the area.
3 Choose Modify > Selective JPEG > Save Selection as JPEG Mask.
4 Change selective quality settings in the Optimize panel if desired.
Note: To undo a selection, choose Modify > Selective JPEG > Remove JPEG Mask.