Specifications

The Digital Fine Print Course

Editing a Fine Print

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Converting Colour Images to Greyscale

There are at least five methods for converting RGB to Greyscale. They are not the same.

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For example: An original 24-bit RGB image contains

three 8 bit channels. An Greyscale image contains only

one channel. Therefore 16-bits of data must be discard-

ed when converting 24-bit RGB to Greyscale. The

Channel Mixer with the Monochrome option selected

allows different percentages of each channel to be mixed

together. If the individual channels are adjusted so as to

equal 100%, then the overall luminosity will be preserved.

Different mixes of the RGB

channels produce different

Greyscale renderings. The

effect is similar to photo-

graphing the original scene

on panchromatic B&W film

through different coloured

filters. If 100% is exceeded,

then the Constant slider

may need to be adjusted, in

this case -10%, to prevent

the highlights blowing out

beyond 100% (255 255 255).

Photoshop>Image>Mode>Greyscale

Photoshop>Image>Adjustment>Desaturate

Photoshop>Image>Mode>Lab then discard the a* and b* channels before converting

Photoshop>Image>Mode>Greyscale to preserve the Lightness channel.

Discard two RGB channels before converting Photoshop>Image>Mode>Greyscale to

preserve that channel as Greyscale.

Custom manage the conversion (mixing) of the three RGB channels to a single

greyscale channel. This can be accomplished via Photoshop>Image>Calculations or

Photoshop>Image>Adjustments>Channel Mixer or Black & White tools.

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