Tone Management System - Measured Luminance

 

Introduction

The first Tone Management System method converts a color image's tones to black and white tones in order to maintain Measured luminance.
 

Tonal Adjustments by Color

The three basic Adobe Photoshop controls for tonal adjustments are Hue/Saturation, Levels and Curves.  Generally, it is best to use Levels or Curves for tonal adjustments.

We can use all three Photoshop controls to adjust tone by color ranges.  We can use Levels and Curves to adjust tone by color channel.

This section of the web site does not go into the details of how to use Hue/Saturation, Levels or Curves to make tonal adjustments.  That information is covered on the Hue/Saturation page, the Levels page and the Curves page.  For in-depth information on how to use Levels or Curves with color ranges, read the Using Levels and Curves with Color Ranges page.

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The first example uses Curves for tonal adjustments by color.  The second example uses Levels.
 

MCC Method

The first method to be discussed converts a color image's tones to black and white tones in order to maintain Measured luminance.  It achieves this by using a Channel Mixer adjustment layer for monochrome conversion.  It then uses a Curves adjustment layer for tone management by color.  The step-by-step instructions on how to use this method are as follows.
 

Create the monochrome conversion layer

Above the image and any existing adjustment layers…

1. Create a Channel Mixer adjustment layer by clicking Layer > New Adjustment Layer > Channel Mixer.  Name the layer as desired.
2. Set the Red channel to 30%.
3. Set the Green channel to 59%.
4. Set the Blue channel to 11%.
5. Leave Constant 0%.
6. Check the Monochrome check box.  See Figure 1 for the proper Channel Mixer settings.  These settings, as well as a Photoshop action that will create this adjustment layer, can be found on the Downloads page.
7. Click OK.
8. Leave blending mode Normal.  For now, turn off the Channel Mixer's visibility by turning off its eye icon in the Layers panel.

 

adjust tone by color range

1. Click Select > Color Range and use the eyedropper tools to select the desired colors. Click OK to create the selection.
2. Below the Channel Mixer adjustment layer, create a Curves adjustment layer by clicking Layer > New Adjustment Layer > Curves.
3. Click OK without making any changes.  The selection created in step 9 is now the layer mask.
4. Change the blending mode to Luminosity.
5. Reopen the Curves adjustment layer.
6. Make the necessary tonal adjustments.  Check the results by turning the Channel Mixer's visibility on and off.  For in-depth information on how to use Curves to make tonal adjustments, read the Curves Adjustments page.  For additional information on using color ranges with Curves, read the Using Levels and Curves with Color Ranges page.

 

Or, adjust tone by color channel

1. Below the Channel Mixer adjustment layer, create a Curves adjustment layer by clicking Layer > New Adjustment Layer > Curves.
2. Click OK without making any changes.
3. Change the blending mode to Luminosity.
4. Reopen the Curves adjustment layer.
5. Using the Channel drop down box in the Curves dialog box (see Figure 2), select the desired channel.
6. Make the necessary tonal adjustments.  Check the results by turning the Channel Mixer's visibility on and off.  For in-depth information on how to use Curves to make tonal adjustment, read the Curves Adjustments page.

 

Steps 1 through 8 convert the color RGB image to a black and white RGB image.  The percentages in steps 2 through 4 are critical for retaining Measured luminance as defined by the Curves control.  Do not change these percentages.  Instead, to change an image's tone, use the Levels or Curves adjustments.  Steps 12 and 17 are critical to ensure the changes we make only affect tone, not color.  Steps 9 through 14, or steps 15 through 20, are where we manage an image's tone by color.
 

make non-color based tonal adjustments

1. Above the Channel Mixer adjustment layer, create a Levels or Curves adjustment layer by clicking Layer > New Adjustment Layer > Levels/Curves.
2. Make the desired adjustments and click OK.
3. Leave blending mode Normal.

 

Summary

The adjustment layers below the Channel Mixer adjustment layer allow us to adjust tone by color range or color channel.  Since the image is black and white 'above' the Channel Mixer adjustment layer, we cannot use color to target our tonal adjustments above this layer.  Therefore, any tonal adjustments we need to make that are not based on color can be made above the Channel Mixer adjustment layer.

Figure 3 is an example of what the Layers panel for the MCC method should look like if done properly.

The advantages of the MCC method are many.  Measured luminance is accurately retained.  We still have control over tonality by color.  The method is non-destructive and, hopefully, predictive and intuitive.

 

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MHL Method

The second method to be discussed is the MHL method.  The MHL method uses Measured luminance, a Hue/Saturation adjustment layer for monochrome conversion, and a  Levels adjustment layer for tone management by color.  The step-by-step instructions to use this method are as follows.
 

 

Create the monochrome conversion layer

Above the image and any existing adjustment layers…

1. Create a Hue/Saturation adjustment layer by clicking Layer > New Adjustment Layer > Hue/Saturation.
2. Make sure the Edit drop down box is Master and set Saturation to -100.  See Figure 4.
3. Click OK.
4. Change the blending mode to Color.  For now, turn off the Hue/Saturation's visibility by turning off its eye icon in the Layers panel.  A Photoshop action that will create this adjustment layer can be found on the Downloads page.

 

adjust tone by color range.

1. Click Select > Color Range and use the eyedropper tools to select the desired colors. Click OK to create the selection.
2. Below the Hue/Saturation adjustment layer, create a Levels adjustment layer by clicking Layer > New Adjustment Layer > Levels.
3. Click OK without making any changes.  The selection created in step 5 is now the layer mask.
4. Change the blending mode to Luminosity.
5. Reopen the Levels adjustment layer.
6. Make the necessary tonal adjustments.  For in-depth information on how to use Levels to make tonal adjustments, read the Levels page.  For additional information on using color ranges with Levels, read the Using Levels and Curves with Color Ranges page.

 

Or, adjust tone by color channel

1. Below the Hue/Saturation adjustment layer, create a Levels adjustment layer by clicking Layer > New Adjustment Layer > Levels.
2. Click OK without making any changes.
3. Change the blending mode to Luminosity.
4. Reopen the Levels adjustment layer.
5. Using the Channel drop down box in the Levels dialog box (see Figure 5), select the desired channel.
6. Make the necessary tonal adjustments.  For in-depth information on how to use Levels to make tonal adjustment, read the Levels page.

 

Steps 1 through 4 convert the color RGB image to a black and white RGB image.  Step 4 is critical to limit the desaturation adjustment to color, not tone.  If we do not change the blending mode to Color, Photoshop will calculate the resulting tone using a different algorithm than it uses to calculate tone when using the Curves control.  (More information about this can be found on the Customary Method - Desaturation page.)  By changing the blending mode to Color, we drastically change the way the Hue/Saturation adjustment layer desaturates an image.  The Color blending mode causes Photoshop to remove the color without affecting luminance.  Steps 5 through 10, or steps 11 through 16, are where we manage an image's tone by color.
 

Make non-color based tonal adjustments

1. Above the Hue/Saturation adjustment layer, create a Levels or Curves adjustment layer by clicking Layer > New Adjustment Layer > Levels/Curves.
2. Make the desired adjustments and click OK.
3. Leave blending mode Normal.

 

Summary

The adjustment layers below the Hue/Saturation adjustment layer allow us to adjust tone by color range or color channel.  Since the image is black and white 'above' the Hue/Saturation adjustment layer, we cannot use color to target our tonal adjustments above this layer.  Therefore, any tonal adjustments we need to make that are not based on color can be made above the Hue/Saturation adjustment layer.

Figure 6 is an example of what the Layers panel for the MHL method should look like if done properly.  Note the blending mode for the Hue/Saturation adjustment layer.

The advantages of the MHL method are many.  Measured luminance is accurately retained.  We still have control over tonality by color.  The method is non-destructive, predictable and, hopefully, intuitive.

 

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Figures 7A and 7B show before and after images using either the MCx or MHx method.

Figure 7A.  The Color RGB Image

Figure 7B.  The Black and white version using either the MCx or the MHx Methods

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Which Adjustment Layer for Monochrome Conversion?

The MCx and the MHx methods give almost identical results.  In my tests, converting to monochrome using the Hue/Saturation adjustment layer (MHx), when used with the correct blending mode of Color, gives slightly more accurate results than Channel Mixer (MCx).  However, the difference is imperceptible (around 1/25 of a stop).  Therefore, we can use either one.  The critical steps are getting the adjustment layers in the proper order and getting the blending modes correct.
 

Which Adjustment Layer for Tone Control by Color?

The first method above uses a Curves adjustment layer to manage tones by color.  The second method uses a Levels adjustment layer.  Which is better?  The one you are more comfortable with.  Levels has the advantage of giving us a histogram so we can readily compare the image's tonal range to the digital tonal range.  Curves has the advantage of giving us more control along the entire tonal range.  Levels and Curves can easily be used to make adjustments by color channel.  With a little bit of additional work, they can also be used with color ranges.  Hue/Saturation gives us the least amount of control over the tonal range, but it is the easiest control to use when working with color ranges.  Hue/Saturation cannot be used with color channels.