Tone Management System - Grayscale

Introduction

In Adobe Photoshop, we can quickly convert a RGB image to true grayscale by clicking Image > Mode > Grayscale and the image is converted to black and white.  However, this method is destructive and does not allow us to manage tone by color.  The methods I devised and discuss here overcome these disadvantages while maintaining grayscale as the desired tonality.

 

Tonal Adjustments By color

The three basic 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, 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.

 

GCC Method

The GCC method preserves Grayscale luminance, uses a Channel Mixer adjustment layer for monochrome conversion, and a Curves adjustment layer for tone management by color.  The step-by-step instructions to use this method are as follows.
 

Copy Original Image

After all global and local changes have been made …

1. Click Image > Duplicate.  Type the name Grayscale RGB and click OK.  If desired, another name can be used.
2. Make sure the Grayscale RGB document is the active document and click Layer > Flatten Image.  If asked to discard hidden layers, then there are layers in the Grayscale RGB document that are not being used.  These layers will be in the Layers panel and they will not have an eye icon .  If these layers are not needed, click OK.  Otherwise, click cancel and activate the layers in both the Grayscale RGB and original documents and repeat step 2.
3. Save and close the original document.

 

At this point, we now have a copy of the original image with all global and local changes applied.  This new document will become the final black and white RGB image.  The reason it has to be copied is to avoid double applying the global and local changes when we apply the grayscale 'filter'.
 

Create Grayscale Filter

1. Click Image > Duplicate again.  Type the name Grayscale and click OK.  Another copy will be created.  This second copy is temporary and will be discarded shortly.

   
   Figure 1.  Using A Grayscale Image As A Luminosity Filter

2. Make sure the Grayscale document is the active document.
3. Click Image > Mode > Grayscale.
4. Click OK when asked to discard color information.
5. In the Grayscale document, rename the Background layer to Grayscale by double clicking the layer name in the Layers panel.  Even though the dialog box says New Layer, type the name and click OK.
6. Rearrange the Grayscale RGB document and the Grayscale document on the monitor so that both can be seen.
7. Make sure the Layers panel is active for the Grayscale document.
8. In the Layers panel, Shift - click and drag the Grayscale layer in the Grayscale document to the Grayscale RGB document.  It is important to hold down the Shift key before pressing the left mouse button and continue to hold down the Shift key until after releasing the left mouse button.  This will ensure the layer is properly centered in the Grayscale RGB document.
9. Make sure Grayscale RGB is the active document.
10. Looking at the Layers panel, if the Grayscale layer is not the topmost layer, drag it to the top.
11. In the Grayscale RGB document, change the blending mode of the Grayscale layer to Luminosity.  Do not be concerned when the colors reappear.  We are using the Grayscale layer to control luminance, not color.  We will remove the color later.  The Layers panel for the Grayscale RGB document should look like Figure 1.
12. Close, without saving, the Grayscale document.

At this point, the only open document should be Grayscale RGB, and its tonality matches that of a true grayscale image even though it is still in color.

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Convert to Black and White

We will now create the necessary adjustment layer to convert the image to monochrome and allow us to control tone by color.
 

Above the image and above the Grayscale layer...

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 2 for the proper Channel Mixer settings.
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 and above the Grayscale 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 24 is now a layer mask.
4. Change the blending mode of the Curves adjustment layer 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 and above the Grayscale 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 of the Curves adjustment layer to Luminosity.
4. Reopen the Curves adjustment layer.
5. Using the Channel drop down box in the Curves dialog box (see Figure 3), 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 16 through 23 convert the color RGB image to a black and white RGB image.  The percentages in steps 17 through 19 are critical for preserving the luminosity from the Grayscale layer.  Do not change these percentages.  Instead, to change an image's tone, use the Levels or Curves adjustments.  Steps 27 and 32 are critical to ensure the changes we make only affect tone, not color.  Steps 24 through 29, or steps 30 through 35, 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

Figure 4 is an example of what the Layers panel for the GCC method should look like if done properly.  Note the blending mode of the Curves adjustment layer.

I realize this appears to be rather involved.  Especially with creating two copies of the image.  However, if the grayscale layer were copied back to the original image, then any global and local changes will be applied twice.  Once as part of the original image and again when the image was flattened and then copied back to the original.

By changing the blending mode of the Grayscale layer, we turned it into a luminosity 'filter'.  Basically, it allows the color to pass through but replaces the luminance in the underlying image with grayscale luminance.  Since color still passes through, we can manage tone by color while retaining grayscale luminance.  The Channel Mixer layer does not replace the grayscale luminance with its own.  Rather it preserves the grayscale luminance.

The advantages of the GCC method are many.  For those who prefer grayscale tone, we preserve grayscale tonality while maintaining the ability to adjust tone by color.  The method is non-destructive and since we are using Curves and/or Levels for tonal adjustments, it is predictable.

There are three main disadvantages.  First, we end up with two images.  Our master image and a black and white RGB version of it.  Second, if we decide to go back and change any of the global and/or local adjustments on the master image, we will have to recreate the black and white RGB image from the beginning.  So it is best to be sure we are done with the color version of the image before working on the black and white version.  Third, because of the number of steps involved, it is not easily intuitive.

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GHL Method

The second method to be discussed is the GHL method.  The GHL method preserves Grayscale luminance, uses 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 Grayscale layer

1. Follow steps 1 through 15 above to create a color copy of the image with a Grayscale layer with a blending mode of luminosity.

 

Create monochrome conversion layer

Above both the image and Grayscale 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 5.
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.

 

 

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 and above the Grayscale 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 a layer mask.
4. Change the blending mode of the Levels adjustment layer to Luminosity.
5. Reopen the Levels adjustment layer.
6. Make the necessary tonal adjustments.  Check the results by turning the Hue/Saturation's visibility on and off.  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.

 

Or, adjust tone by color channel.

1. Below the Hue/Saturation adjustment layer and above the Grayscale 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 of the Levels adjustment layer to Luminosity.
4. Reopen the Levels adjustment layer.
5. Using the Channel drop down box in the Levels dialog box (see Figure 6), select the desired channel.
6. Make the necessary tonal adjustments.  Check the results by turning the Hue/Saturation's visibility on and off.  For in-depth information on how to use Levels to make tonal adjustment, read the Levels page.

 

Steps 2 through 5 convert the color RGB image to a black and white RGB image.  Step 5 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.  (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 with 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 7 is an example of what the Layers panel for the GHL method should look like if done properly.  Note the blending mode for the Hue/Saturation adjustment layer.

The advantages of the GHL method are many.  Grayscale luminance is accurately retained.  We still have control over tonality by color.  The method is non-destructive and predictable.

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Figures 8A and 8B show before and after images using either the GCx or GHx methods.

Figure 8A.  The Color RGB Image

Figure 8B.  The black and white version using either the GCx or the GHx methods

 

 

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Which Adjustment Layer for Monochrome Conversion?

The GCx and the GHx methods give almost identical results.  In my tests, converting to monochrome using the Hue/Saturation adjustment layer (GHx), when used with the correct blending mode of Color, gives slightly more accurate results than Channel Mixer (GCx).  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.