MLUnsold Digital Imaging

Shift Hue and Enhance Saturation and Luminance

The Hue-Saturation-Luminance command shifts a hue range to a different range with optional saturation and luminance adjustment. All Colors is the default hue range. The Color drop list box is used to select the default red, yellow, green, cyan, blue, and magenta range.

* The Map From color spectrum bar with feather and range triangles is used to define the hue range to shift.

* The Map To color spectrum bar shows the shifted color spectrum.

* The luminance and saturation sliders are used to increase or decrease luminance and saturation only in the hue and feather range.

The goal of this example is to shift the salmon color of a bicolor narrow band image to a hue that is closer to H-alpha red. The same technique can be used to correct the salomon color common in H-alpha and color combinations from a DSLR or one shot color CCD.

Step 1 - Open the bicolor image and the Color | Hue-Saturation-Luminance Tool

The bicolor image was created by assigning red to H-alpha, the average of H-alpha and OIII to green, and OIII to blue or (R,G,B) = (Ha, 0.5Ha + 0.5OIII, OIII). This bicolor assignment and also mixing DSLR H-alpha and color leads to a salmon color for red instead of the correct H-alpha red.

Step 2 - Select the Salmon Hue from the Image

Check the Select Hue From Image box on the Hue-Saturation-Luminance tool then left-click on the salmon hue in the image to set the hue and feather triangles.

Step 3 - Shift Salmon to Red

Move the Hue slider to the left to shift salmon towards red. Move the Saturation slider to the right to increase saturation. The hue shift and saturation increase only affect the hue range inside the hue and feather triangles.

Step 4 - Adjust the Left Hue Feather Range

The left hue feather triangle is moved into the blue range to increase blue and blend the hue shift. Note the increase in blue and smooth red.

Step 5 - Adjust the Right Hue Feather Range and Hue Range

Move the right feather hue trianle towards the right to include more yellow green. Left-click between the right two triangles and move them as a group towards the left to increase the hue range. Left-click between the two black range triangles and move all four traingles as a group to adjust the final hue shift.

Salmon Hue Shifted to Red

Salmon has been shifted to red but a magenta hue in the bright areas and brightest star remains from the initial image. The Selective HSL Color Balance tool can be used to change bright magenta into red.

The bicolor image was created by assigning red to H-alpha, the average of H-alpha and OIII to green, and OIII to blue or (R,G,B) = (Ha, 0.5Ha + 0.5OIII, OIII). This bicolor assignment and also mixing DSLR H-alpha and color leads to a salmon color for red instead of the correct H-alpha red.

Check the Select Hue From Image box on the Hue-Saturation-Luminance tool then left-click on the salmon hue in the image to set the hue and feather triangles.

Move the Hue slider to the left to shift salmon towards red. Move the Saturation slider to the right to increase saturation. The hue shift and saturation increase only affect the hue range inside the hue and feather triangles.

The left hue feather triangle is moved into the blue range to increase blue and blend the hue shift. Note the increase in blue and smooth red.

Salmon has been shifted to red but a magenta hue in the bright areas and brightest star remains from the initial image. The Selective HSL Color Balance tool can be used to change bright magenta into red.