Photoshop Tutorials
The Design Center, DT&G / Photoshop Department / Black & White from Color #1 / Using Channels / Using Calculations  

Barry Huggins shares his Photoshop Retouching Portraits expertise in this issue of DTG!

Creating Black & White from Color

Method 3: Calculations

original colorUsing the channels straight out of the box works brilliantly, as long as one of the channels gives you the desired result. If not, some manual mixing is the best solution. The Calculations command is your best resort -- don't let the name put you off, as no math on your part is required. This image of the bell and cross is our next challenge.

1 Checking the channels shows that the Red channel offers the best contrast between the sky and white cross. However it's not very strong and the range of tones isn't varied enough to create a strong result.

2 Keep the Red channel active and go to
Next Step Image > Calculations.
Because the Red channel was active, the Red channel appears in the Calculations dialog box. Source 1 and 2 are set to the same document, layer, and Red channel, which means they will be combined for the calculation to take place.

using channels

The blending drop-down is set to Multiply. This works in exactly the same way as the normal layer blend modes. Multiply will darken the image, but based on the red channel. Therefore blue elements or elements with a blue cast will become darker than other elements.

Set the Result drop-down box to New Document to create a new multichannel file based on the calculated result.

3 In this case, multiplying the Red channel works perfectly. The blues are darkened, creating this bold final image.

 

Combine Red and Green Channels

USING THE BLENDING OPTION

For a slightly less dramatic result, try combining the Red and Green channels, again using the Multiply blend mode. The difference is subtle, but it demonstrates the fine control you have using this technique.

The Channel Mixer

Staying within the context of mixing and calculating channel values, another powerful option is the aptly named Channel Mixer. This command allows us to mix the values of each of the channels, providing us with an enormous variety of combinations. In this shot there should be no mistaking the flower from the leaves and stem. However, after desaturation the greens and pinks merge.

1 Make sure the RGB composite channel is active, then go to
Next Step Image > Adjustments > Channel Mixer.
Enable the Monochrome checkbox.
Changing the percentage values for each of the Red, Green, and Blue channels will dramatically influence the image. Traditional black-and-white photographers might consider using a green color filter here, as this will lighten the greens of the foliage and darken the pink flower (pink is almost complementary to green).
To emulate this in the Channel Mixer, change the values by boosting green and diminishing red.

The Channel Mixer

2 The result is very different from the original desaturated version. We can use the idea of a color filter as a guiding principle here, or just adjust the settings by eye. The main thing to keep in mind is that the total percentage value of all channels combined should be roughly around 100% with a variance of 20% or so.

Your eyes will tell you this as you experiment -- any extreme value above or below 100% simply won't look good.

Previously: Black & White from Color Next Step #1 Using Desaturate Next Step #2 Using Channels

 

 

Photoshop Retouching Cookbook for Digital Photographers with 113 Easy-to-Follow Recipes to Improve Your Photos and Create Special Effects By Barry Huggins ... tells you everything you need to know to adjust, correct, retouch, and manipulate your photographs-without making you first learn everything there is to know about Photoshop CS2. Sample Excerpt: Motion Blurring and Removing Skin Blemishes & Wrinkles (PDF Format)

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