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You Are Here: Home > Gear > Digital Editing > Selectively Grayscaling a Color Photo

 

USING THE CHANNEL MIXER TO SELECTIVELY GRAYSCALE A COLOR PHOTO IN PHOTOSHOP

Background Information: This method of selectively grayscaling images was originally done just out of novelty, but since a lot of people have been asking about how it is done, I've included it in the Digital Editing section. The instructions were made using Photoshop 7 but should apply to Photoshop 6 and 5(?) also.

 

1) Open your color photo in Photoshop and adjust the levels so that the image appears as you would want it, if you were to keep it as a color image.

Original Color Image

 

2) If the photo is not already in 8 Bit RGB mode, convert it to 8 bit RGB mode now.

3) Under the Layers Palette, click the Adjustment Layers icon (the half black circle at the bottom of the palette). Click on Channel Mixer from the menu to make a Channel Mixer Adjustment Layer.

On a side note, you should use Adjustment Layers for your edits whenever possible because they allow you to modify your image in a non-destructive manner. This means that when you are using Adjustment Layers to make your image brighter, less blue, B&W, or whichever edit you are choosing, the underlying image is never altered. Photoshop just keeps track of the edits you are making on the adjustment layer and applies them to the images underneath for display on your monitor or for exporting. The advantage here is that since the data in your underlying image is never altered, you can make as many edits as you want without degrading the image, remove your edits altogether if you change your mind later on, or in the case of this exercise, selectively apply them.

Create a Channel Mixer Adjustment Layer

 

4) Click the Monochrome checkbox on the Channel Mixer panel. This tells the Channel Mixer to convert each pixel to a grayscale value based on the color information. And because the color information is still there, you can use this information to adjust the way the image will look by weighing the colors differently, which is basically what happens when you use color filters in the analog world. Just slide the RGB sliders to choose which colors you want to use to determine the grayscale values. For instance, if you set you Red channel to 100% and the Green & Blue channels to 0%, this is similar to taking a B&W photo with a deep red filter because only red light is being used to render the B&W image.

The RGB ratio of 30/60/10 usually works well for most pictures. If you want darker skies though, a little more red and less blue should be used. In some instances such as the in the photo of the Cham Towers of Po Nagar in Vietnam, I will gain the red channel to over 100% and the blue channel into negative range to get a pseudo-infrared effect. For portraits, too much red will make people look like they're glowing so emphasis on the green channel is usually best here. Play around with the ratios to see which one you like best but keep in mind that you'll usually (but not always) want the ratios to add up to ~100%.

Use the Channel Mixer to Grayscale Your Image

 

5) Take a look at your layers palette. You'll notice the Adjustment Layer comes with a Layer Mask. This mask is represented by the rectangle on the right side in the Adjustment Layer. The Layer Mask allows you to select the areas of the image your Adjustment Layer affects. This selecting is done by painting the Layer Mask. The areas on the Layer Mask which are painted black will block out the effects of the Adjustment Layer while the areas painted white allow the Adjustment Layer to affect the images underneath. The effects are not binary so you can use shades of gray to paint areas which you want to be effected by the Adjustment Layer to a lesser degree. By default, the entire Layer Mask is painted white so the Adjustment Layer affects the entire image.

When painting the Layer Mask, make sure it is active. You can determine this by looking in the box to the right of the eye icon. The square symbol with a hole in it indicates that the Layer Mask is active. If you don't see the symbol, click on the Layer Mask icon (the rectangle to the right of the Adjustment Layer icon).

Using the Layer Mask

 

6) With the Layer Mask active, paint the areas you want returned to color with black paint. When your layer mask is active, the paint doesn't go on the image but the Layer Mask so don't worry about it putting black on your image. As mentioned above, the black paint is used to block out the effect of your adjustment layer, which in this case is the Channel Mixer trying to make your image B&W. Set the hardness of your brush below 50% so that the transition edges don't look too hard. If you make a mistake painting the layer mask, remember you can always paint that area with the opposite color to undo the mistake. To see how the Layer Mask looks, click the Layer Mask icon while pressing Alt.

The Selectively Grayscaled Image

 

Your photo is now only grayscaled in the areas you want it to be.

 


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