Getting Great Grayscale images from RGB digital files
Here's one of the methods that I've stumbled upon for creating
good black and white (grayscale) images from RGB digital files (scanned
film or digital camera files). I make no claims that this is the
only or the best way, it's simply a way that I've found gets me
to a usable image in a reasonable number of steps, and works well
in production situations.
I'm going to outline the first four steps in fairly explicit detail,
but you should understand that you can easily go on from there and
blend in additional alpha channels to lighten or darken specific
colors. While it is possible that this can be made into a photoshop
action, it often requires a fair amount of tweaking unless you are
dealing with a large number of very similar images.
"DR Custom grayscale" technique:
Preamble. The range of values I give below work well with images
that start as full scale (RGB 3 to 5 for blacks, and 247 to 252
for whites) Colormatch RGB images. If you are starting with images
that are in Adobe RGB, or full out 0 to 255 values you may need
to "extrapolate" and experiment.
1. Change from RGB colorspace to LAB
2. Choose the lightness layer (from the Channels
palette), from the IMAGE menu then choose Calculations.
A dialog box will appear with a bewildering number of options. There
are essentially four main areas, Source 1, Source 2, Blending, and
I'm going to tell you what to change, the default will be for Source
1 and Source 2 to be the name of the current file.
Leave these as they are, also leave the "Layer" selection
at "Background." Provided that you have chosen the "Lightness"
channel, "Lightness" should be the default selection for
Change the "Blending" mode to "Multiply"
Set Opacity to a value between 40 and 60 percent. This will affect
the shadow areas disproportionately more than the highlight values.
Aim for solid blacks in the darkest parts of your image, with the
detailed shadow areas just barely visible.
The "Results" area will be set to "New Channel"
as default, leave this as is.
Choose OK, and the result of the calculation will
appear as "Alpha 1" in the Channels Palette.
3. Choose the Lightness channel a second time
from the Channels Palette.
Choose Calculations from the Image Menu a second time.
Repeat the operation outlined above EXCEPT with a change in the
"Opacity" field (in the blending area) to 5 percent.
The result will be a slighly denser lightness channel, but will
appear washed out. Click OK, and the result of the calculation will
appear as "Alpha 2" in the Channels Palette.
4. Leave Alpha 2 selected in Channels Palette.
Choose Calculations from the Image
Menu a third time.
This time change the Source 1 "channel" to "Alpha 1" and
change the Blending mode to "Hardlight"
Set Opacity to between 40 and 50 percent. We are looking for an
effect similar to a grade 3 paper as in days of old. Click OK, and
the result of the calculation will appear as "Alpha 3"
in the Channels palette.
For some of you this may be a result you wish to keep. I usually
find it necessary to "temper" the result a bit, so I add one more
5. Leave Alpha 3 selected in the Channels
Choose Calculations from the Image
Menu a fourth time.
Change Source 1 to Alpha 2 (the weak washed out
Change Blending mode to "Normal" Set Opacity to "taste"
(typically between 40 and 60 percent).
If you are happy with the result, click OK, and the result will
appear as "Alpha 4" in the Channel Palette.
Sometimes you may be getting too dark of a shadow area. If this
is the case try reversing the sources, by setting Source 1
to "Alpha 3" and Source 2 to "Alpha 2"
and play with the opacity setting.
When you are satisfied, convert the result to Grayscale (discard
color), and continue on from there.
If you feel that the blue sky should be a little deeper, or what
was an orange colored object is too close in value to a light blue
object, then try converting to RGB (the "Alpha 4" channel
will remain selected).
Inspect the R, G, and B channels. If you are wanting to make the
sky darker, you'll find that the R (red) channel will have a much
darker result. Lets assume that's what we want for this example.
If so, set Source 1 to the "R"(red) channel
The "Normal" blending mode set at 50 percent opacity may
look OK, but you may want to experiment and see what happens with
it set to "Darken" or "Overlay" as well.
Sometimes you may wish to lighten a particular color, and that's
possible as well. Usually the "lighten" or "screen" mode will be
needed in these cases. Set the Source 1 to the color you
wish to lighten and set the blending mode to "lighten" or "screen"
and adjust to taste.
As above, when you are satisfied, convert the result to Grayscale
(discard color) and save in your choice of file format.
In some very drastic situations (usually when handling imaging
chores for a client that supplies their own scans or prints) I've
had to resort to doing a separate calculation for one color or tonal
value. I then duplicate the image, convert the best channels to
grayscale, and then drag the "correcing" layer on top of the other
(holding the shift key down to align).
I apply a "layer mask" typically the "Hide All"
variety, and "paint on the mask with a white brush to change the
tonal value of that specific area. It's easier than burning and
dodging, as the results are completely reversable, even after saving
the image (provided you saved it as a PSD file with alpha channels
I downloaded the two color images that Keith Cooper shared as part
of a page he has posted showing
the effects of different methods of converting images to black and
white. I processed both according to steps 1 to 5 above. I also
did a few variations with differing opacities and switching the
Alpha 2 and 3 layers in the final blend.
You can see some of those variations on his Northlight-images site
labeled as "DR custom" at the URL above.
In addition Uwe Steinmueller has posted some variations inspired
by these original instructions on the Prodig
List and posted them on his Digital
Photo Outback site.
When I get a chance I'll try to post a few screen captures and
image samples, till then these step-by-step instructions should
get you started.
David Riecks, please do not distribute without permission from the
back to "digitalinfo"
This page last updated: May, 2004