Modifying Red, Green, and Blue Channels
Chapter 14, Colour Grading: RGB and Hue Curves

Topics on this Page:

Shifting Hue

Saturating and Suppressing Colours

Modifying Image Luminance

Modifying Image Lightness

Modify curves to adjust the hue, saturation, luminance, and lightness of an image. You can:

• Perform hue shifts.

• Suppress or saturate colour ranges.

• Suppress or saturate luminance ranges.

• Lighten or darken colour ranges.

• Add vertices to the curves to refine your adjustments.

Shifting Hue

Shift the hue of the entire image or a range of colour in the image.

1. Indicate the colour grading stage at which the curve modification is being applied:

   • To work on the initial primary grade, click Input.

   • To make curve modifications for secondary colour grading, enable a secondary layer.

2. Click the Hue button located below the RGB button, and then click the upper Hue button to display the Hue curve.

   

   The Hue curve is plotted to the Hue spectrum.

3. Sample the colour you want to use as a reference for your adjustments. See Plotting Colour Values when Adjusting Curves.

   A vertical line representing the reference colour is plotted on the Hue curve.

4. Drag vertices up or down to shift the hue of the colour displayed in the hue spectrum.

   

   The hue of the selected colours moves through the hue spectrum as you drag.

   Hint: You can also select a vertex to use tangent handles to adjust the curve.

5. Modify the curve until you are satisfied with the results:

   • To select a vertex, click it. To select several vertices, draw a selection box around them.

   • To move several selected vertices, select them and then drag one. To restrict vertex movement to the Y axis, press Shift while moving the mouse. To restrict vertex movement to the X axis, press Shift+Alt.

   • To add a vertex to the curve, place the mouse cursor over the area on the curve where you want to add the vertex and then press A.

   • To lock the curve in place while adding a vertex, press Shift+A on the curve.

   • To delete vertices, select them and then press D.

Saturating and Suppressing Colours

You can adjust the purity of colours in the image by modifying the saturation. You can suppress or saturate colours in a range or across the entire image.

1. Indicate the colour grading stage at which the curve modification is being applied:

   • To work on the initial primary grade, click Input.

   • To make curve modifications for secondary colour grading, enable a secondary layer.

2. Click Hue and then click Sat to display the Saturation curve.

   

   The Saturation curve is plotted to the hue spectrum.

3. Sample the colours you want to use as a reference for your adjustments. See Plotting Colour Values when Adjusting Curves.

   A vertical line representing the reference colour is plotted on the Saturation curve.

4. To select a vertex, click it. To select several vertices, draw a selection box around them.

5. Saturate or suppress the colour:

   • To saturate the colour displayed in the hue spectrum, drag selected vertices up.

   • To suppress the colour displayed in the hue spectrum, drag selected vertices down.

   

   Hint: You can also select a vertex to use tangent handles to adjust the curve.

6. To move several selected vertices, select them and then drag one. To restrict vertex movement to the Y axis, press Shift while moving the mouse. To restrict vertex movement to the X axis, press Shift+Alt.

   

   Hint: To create a greyscale image, select all the vertices and then drag them all the way down. You can then drag vertices up to saturate isolated ranges of colour.

7. To add a vertex to the curve, place the mouse cursor over the area on the curve where you want to add the vertex and then press A. To lock the curve in place while adding a vertex, press Shift+A on the curve.

8. To delete vertices, select them and then press D.

9. Edit the curve until you are satisfied with the results.

Modifying Image Luminance

The Luminance curve represents the gamut of light from black to white. Use the Luminance curve to saturate or desaturate different luminance areas by adding or removing hue from black and white points. Like any other curve, you can add points to refine ranges of an effect.

1. Indicate the colour grading stage at which the curve modification is being applied:

   • To work on the initial primary grade, click Input.

   • To make curve modifications for secondary colour grading, enable a secondary layer.

2. Click Hue and then click L-S to display the Luminance curve.

   

   The Luminance curve is plotted to the hue spectrum.

3. Sample the luminance areas you want to use as a reference for your adjustments. See Plotting Colour Values when Adjusting Curves.

   A vertical line representing the reference colour is plotted on the Luminance curve.

4. To select a vertex, click it. To select several vertices, draw a selection box around them.

5. Saturate or suppress the luminance area:

   • To saturate the luminance area displayed in the hue spectrum, drag selected vertices up.

   • To suppress the luminance area displayed in the hue spectrum, drag selected vertices down.

   

   Hint: You can also select a vertex to use tangent handles to adjust the curve.

6. To move several selected vertices, select them and then drag one. To restrict vertex movement to the Y axis, press Shift while moving the mouse. To restrict vertex movement to the X axis, press Shift+Alt.

   

7. To add a vertex to the curve, place the cursor over the area on the curve where you want to add the vertex and then press A. To lock the curve in place while adding a vertex, press Shift+A on the curve.

8. To delete vertices, select them and then press D.

9. Edit the curve until you are satisfied with the results.

Modifying Image Lightness

Increase or decrease the lightness in specific colour ranges or across the image.

1. Indicate the colour grading stage at which the curve modification is being applied:

   • To work on the initial primary grade, click Input.

   • To make curve modifications for secondary colour grading, enable a secondary layer.

2. Click Hue and then click Light to display the Lightness curve.

   

   The Lightness curve is plotted to the hue spectrum.

3. Sample the colours you want to use as a reference for your adjustments.

   A vertical line representing the reference colour is plotted on the Lightness curve.

4. To select a vertex, click it. To select several vertices, draw a selection box around them.

5. Modify the lightness:

   • To increase the lightness of the colour displayed in the hue spectrum, drag selected vertices up.

   • To decrease the lightness of the colour displayed in the hue spectrum, drag selected vertices down.

   

   Hint: You can also select a vertex to use tangent handles to adjust the curve.

6. To move several selected vertices, select them and then drag one. To restrict vertex movement to the Y axis, press Shift while moving the mouse. To restrict vertex movement to the X axis, press Shift+Alt.

7. To add a vertex to the curve, place the cursor over the area on the curve where you want to add the vertex and then press A. To lock the curve in place while adding a vertex, press Shift+A on the curve.

8. To delete vertices, select them and then press D.

9. Edit the curve until you are satisfied with the results.