HOW TO USE ADOBE PHOTOSHOP'S 'MERGE TO HDR' FUNCTION TO ENHANCE YOUR ASTROPHOTOS.
The example lunar below images are not very good astrophotos, but they serve the purpose of illustrating how the HDR function in Photoshop can be used to make better astrophotos. Use this technique on Saturn to capture the crepe ring and the cloud bands of the planet in the same photo. On Jupiter images, use this technique to capture the detail in the central area of the disk as well as the limb areas that are rarely captured at their proper exposure.
Step one: capture at least three video streams of increasing exposure value. One should be just dim enough to not allow blown hightlights. The brightest video should be bright enough to reveal those pesky dim features.
Step two: Process the video streams as usual in your favorite stacking software. Just remember not to adjust the brightness - leave the final image as dim as the original video stream was.
Step Three: Load up Photoshop CS2 or CS3 and choose the "Merge to HDR" automated function from the file menu. Follow the instsructions for merging your three images. Don't forget to make a final tonal adjustment.
| Image No. 1. Note the detail in the upper right corner is intact, while the detail near the terminator at the lower left is lost in the shadows.
Image No. 2 is close to properly exposed but there is still lost detail at the lower left.
Image No. 3 is overexposed for the bright area at the upper right, but this was necessary to bring out the detail at the lower left.
Wouldn't it be great to have a single image that captures the wide dynamic range of values that no single exposure can? The last image is a 'merged' image of the above three images. There is plenty of detail at the lower left terminator and, Voila!, the bright highland area at the upper right is properly exposed.
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