To greatly compress the dynamic range of an image, set Permanent Stretch Type to Log, Input Range to Max Pixel, and Output Range to Unlimited. In this mode, you can adjust the Screen Stretch of the image window to change the Input Range settings the Min and Max fields will update as you adjust the stretch. To prepare a file for export to a JPEG, BMP, 8-bit PNG, or 8-bit TIFF format, set Permanent Stretch Type to Linear Only, Input Range to Screen Stretch, and Output Range to 8 bit. Various effects can be achieved with the Stretch command the following are some suggestions you can try: Notice how the faint outer details in the comet are enhanced, but the brighter details are still visible. You can toggle back and forth between the processed and original version of the image using the Undo and Redo buttons on the Toolbar. Now set the screen stretch to Low using the Screen Stretch window. We can better control the amount of dynamic range compression by changing the Permanent Stretch Type to Gamma. As you can see in the Preview Image, these settings will dramatically compress the dynamic range of the image so that the brightest and faintest parts of the comet are both visible at once. Set Permanent Stretch Type to Log, Input Range to Manual Settings, and Output Range to 16 bit (0 - 64K).

Press the Stretch button on the Toolbar to bring up the Stretch dialog. (For help on opening files see the Open a File Tutorial). If you have not already done so, open the DG_HaleBopp.fits file in the Samples directory. These operations are performed with the Stretch command. You might also want to try a 'non-linear stretch' to compress the dynamic range of the image. For example, you might want to adjust an image so it will fit in the 8-bit range of a JPEG file. Although the Screen Stretch window allows you to adjust the brightness and contrast of the image on the screen, sometimes you want to change the data in the image buffer.

Pixel stretch after effects