General Stretch Functions

Initial very dark stacked H-alpha image of M42. Note the size of the overexposed core of M42. The dark background will be stretched without increasing the brightness or size of the overexposed core.

Step 1

Hybrid ArcSinH is a very aggressive stretch. The controls in the Stretch and Pre-Stretch Scale groups will be adjusted next.

Step 2

Set the Power slider to 0.868 and White Point slider to 4.530 to increase the background. The HDR Pre-Stretch Scale controls are used to map the image data [black point, white point] to different parts of the same stretch function selected in the Stretch control group. This allows a very great amount of control over the background and highlight areas of the stretched image.

Step 3

Background weight is moved right to 0.85125. As a result background brightness is decreased with an increase of contrast. If the slider is too sensitive use the Background Weight Range list box to adjust the slider sensitivity to match the image.

Step 4

The Power slider of the Stretch control group is moved to 0.630 to increase the overall highlights. Note the core of M42 is the same size as in the initial image above but the background has a very aggressive stretch applied. Star size is smaller when Hybrid ArSinH is used to stretch the image compared to other stretch functions.

Step 5

Final stretched image with smoothed background. Backgound smoothing using the 8-16 bit histogram to set a min-max apply range with feather radius is shown by the feathered background smoothing example.

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