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.

This is a picture of the feature being described.

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. Select Modify > Selective JPEG > Save Selection as JPEG Mask.
  3. Select 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. Select 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. Select 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. Select Modify > Selective JPEG > Save Selection as JPEG Mask.
  4. Change selective quality settings in the Optimize panel if desired.

    NOTE

    To undo a selection, select Modify > Selective JPEG > Remove JPEG Mask.