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Some techniques for converting a color image to black and white
Posted by: Leah on 12-31-1969.

"An overview of some of the most popular alternatives to the "standard" Photoshop monochrome conversion. Based around Photoshop 7, but the same principles apply to any image editing application that allows adjustment layers and/or channel splitting. "

Converting color images to black and white

While many digital cameras offer the option of shooting directly in black and white, far greater flexibility may be obtained by shooting in color and adjusting later to produce a dramatic monochrome image.

We shall explore the various options with reference to the following image, courtesy of .

Figure 1: Original color image

This tutorial refers to Photoshop 7 settings, but the same principles apply to any image editing application that allows adjustment layers and/or channel splitting.

1. Photoshop's default greyscale or desaturation

You can get a look at Photoshop's default by opening your full-color image and then performing any of the following commands:

  • Image -> Mode -> Greyscale
  • Image -> Adjustments -> Desaturate
  • Image -> Hue/Saturation -> Saturation -100
  • Layer -> New Adjustment Layer -> Hue/Saturation -> Saturation -100

All of these commands produce, in their varying ways, a monochrome image based on Photoshop's assumed ratio between the Red, Green and Blue channels. Photoshop will take approximately 30% of the Red channel, 60% of the Green channel and 10% of the Blue channel and combine them to create a monochrome image. This may be the best option, and will generally produce an acceptable result, but it does not provide any control.

Figure 2: Photoshop's default monochrome conversion

2. Using individual RGB channels

This is potentially the next easiest thing to try. Go to the channels palette and select the Red, Green or Blue channel. Each channel will have its own characteristics and mood. If you want to isolate a particular channel, then activate it in the Channels palette and then perform Image -> Mode -> Greyscale to eliminate the other colors (alternatively, if you want to keep the image in RGB mode for now, use the "Channel Mixer" technique below and specify 100% of the channel you want and 0% of the other two). Reducing the image to a single monochrome channel may help to produce more dramatic images than the default Photoshop modes.

Examples of images constructed from one channel only:

Figure 3: Red channel

Figure 4: Green channel

Figure 5: Blue channel

3. Using the Luminosity

Change the mode of the image to Lab (Image -> Mode -> Lab color), then either activate the L channel and convert to greyscale (Image -> Mode -> Greyscale) or use the "Channel Mixer" technique to isolate 100% L channel.

Figure 6: L channel from Lab mode

4. Channel Mixer

One useful technique for creating dramatic images is to make use of the Channel Mixture feature (Image -> Adjustments -> Channel Mixer, or use a Channel Mixer adjustment layer). Make sure the "Monochrome" box is checked. Then adjust the various sliders throughout the performance, making sure the "Preview" box is checked to enable you to see the effects of your changes. Assuming that your starting image was correctly exposed to start with, the only "rule" is to make sure that the percentages of red, green and blue add up to 100%.

For example:

Figure 7: Channel mixer: Red +60%, Green 0%, Blue +40%

Figure 8: Channel mixer: Red +34%, Green +140%, Blue -72%

Just to be confusing, Digidaan (best known for another technique, see below) also came up with a range of Channel Mixer presets that you will see people refering to on the web, in particular "OF" (orange filter) settings. These are Red +78%, Green +22%, Blue 0% and are designed to look as though the image was shot in black and white through an orange filter (useful for increasing drama in skies).

Figure 9: Channel mixer: Red +78%, Green +22%, Blue 0% (the "OF" setting)

5. Digidaan

The "Digidaan technique" (check out Digidaan's website at ) is easy to try and can be more intuitive than messing around with the channel mixer.

The basic process depends on creating two Hue/Saturation adjustment layers. Create the first Hue/Saturation adjustment layer directly above your image layer and set its blend mode to Color, but don't touch any of the sliders at this point. Then add a second Hue/Saturation layer above the first one; leave its blend mode as Normal and drag the Saturation slider all the way to the left (-100) to desaturate.

Now open up the settings for your first Hue/Saturation layer (the one set to Color) and start playing with the Hue slider. By moving this around you are effectively changing the proportions of the colors in the original image that go to make up the black and white result. Once you find an effect you like, you can also try adjusting the Saturation slider to make it stronger or weaker.

Figure 10: Digidaan technique: Master Hue -180, Saturation +46

By default you'll be adjusting the hues as a whole. You can produce more complicated effects by adjusting the hues for individual color ranges. In the pull-down box at the top of the Hue/Saturation settings, to the right of the "Edit:" label, where it normally says "Master", select one of the color ranges and adjust the settings just for that range. Then repeat for other color ranges until you get the look you're after.

Figure 11: Digidaan technique: Reds Hue +84, Saturation +65; Yellows Hue -180, Saturation 0; Greens Hue -26, Saturation +35; Blues Hue +180, Saturation 0

6. Conclusion  

This has just been a brief look at some of the alternatives to the standard, one-size-fits-all Photoshop conversion to monochrome. All of these techniques are easy to apply, and there is potential to follow any of them with spot editing (using Dodge and Burn tools, for example) to fine-tune the result. With a little experimentation you should be on your way to creating some truly dramatic black and white images!

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