ArcSinH - Increase Brightness and Contrast With HDR and Color Decompression

Initial very dark stacked color image of M13. The dark background will be stretched to show faint outer stars without over stretching the bright core. Star color will be increased.

Step 1

Power is set to 0.395. If the Power slider is too sensitive for a given image then use the Power Range list to adjust slider sensitivity to match the image.

Step 2

Nth Root pre-stretch scale is used with Root = 0.916. As a result background star brightness is increased with an increase of contrast. Very little additional stretch is applied to the core of M13.

Step 3

The Background Weight slider has been moved to the left to 0.91750 to even the background. If the slider is too sensitive use the Background Weight Range list box to adjust the slider sensitivity to match the image. The stretched image now shows faint outer stars and color.

Step 4

Color decompression preserves color present in the initial stacked image and does not add new color. Red and blue are enhanced by moving their sliders to the right since red and blue are the dominate colors in this image of M13. The green slider has little effect since the M13 image has very little green. Adjust the red, green, and blue sliders to get good color without artifacts. Check the color adjustment using a full resolution crop.

Step 5

Check the Select Background Point box then left-click on the image to select several background points. The color near each point is balanced. To automatically flatten each color balanced point to the same level select the Balance All Points To Target Level option. The default target level is dark gray or 5120 on a 16 bit scale. Color balance and level of each adjustment point can also be adjusted manually using the red, green, blue, and level sliders.

Step 6

The left and right sides of the histogram do not extend to 0 black and 255 white, respectively.To set the black point green triangle left-click under the histogram at its left edge. To set the white point blue triangle right-click under the histogram at its right edge. Press the Set Min Max Apply button to open the tool selection window.

Check Levels then press Ok.

Step 7

Press Apply on the Levels tool to correct the black and white points. The histogram now extends from left black = 0 to white = 255.

Step 8

Finest and fine background levels are smoothed using a feather radius of 2523 and luminance range with minimum and maximum apply levels of 0 and 13510.

Step 9

Stars are sharpened using the high pass filter option with Add Scaled Mask to Amplitude option checked and slider set to 0.344. As a result stars which are higher frequncy objects are sharpened since their frequency amplitudes are increased.

Step 10

Contrast and overall color is increased using the luminance curve with soft light blend mode set on the Process History window.

Blue increase also with soft light blend mode.

Final ArcSinH stretched image with color decompression ready for further background smoothing, deconvolution, and fine color adjustment as needed.

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