Color to black-and-white conversions
Converting from a color Photo CD image into black-and-white
is not always a simple task. The Photo CD file contains one component
- Y - whose function is to record the black-and-white elements
of the image. Remembering the roots of YCC color in broadcast
television can we assume that the Y element in a Photo CD document
will represent the black-and-white photo correctly? For a large
majority of images, yes. But for some, there are better derivations
for monochrome than to accept the Y channel alone.
Conversions from color to black and white are often better when
you take one channel from an RGB image, or when two channels
are blended together using Photoshop's Calculations options.
Shown here are eight variations-on-a-theme, each labeled with
its source channels. In this case the blend between Red and Blue
creates the best monochrome images (L stands for Lightness, the
black and white component of the CIELAB file.)
Adobe Photoshop software allows a simple mode change to convert
from any color space into black-and-white which it calls gray
scale. After one warning alert, the program reduces the files
colors into a single channel of grayscale information, usually
with good results. There are many occasions when the conversion
should be made more carefully, though.
Using Photoshop's calculations controls, it is possible to blend
one channel into another, weighting the resulting image with
either more or less of the key channel To accomplish this bring
up the rechannels palette and carefully analyze each channel
for strength and tonal benefits Depending on the image content
red or green will often look better than blue. Or, blue and red
will look good while green will look bad.
Choosing the two best channels and giving 50 percent value to
each it is possible to blend the chosen two together to yield
an excellent monochrome image It is a good idea to make the mode
conversion in Photoshop software also, as a comparison and then
keep the one that looks bests Images with strong green or red
elements will benefit from the careful conversion because these
colors are usually abused in a simple mode change conversion
For the more challenging originals a blend favoring one channel
will result in a better product for example giving 75 percent
weight to red and 25 percent to green will occasionally produce
a much better image.
