|Inside Photoshop: From Color to B+W, basics and beyond by Lee Varis|
Many times we are confronted with the need to turn color imagery into B+W. This may be simply because the requirements of the reproduction process demand it or we may actually desire it for aesthetic reasons. Often the process of converting from color to B+W is treated as a trivial mode change followed up with contrast enhancing curves. Photoshop provides many options for creating monochrome images and once you become aware of the types of controls available a whole new creative frontier opens up for you to explore. Photoshop can truly become the ultimate B+W darkroom allowing the artist, in pursuit of photographic artistry, to go well beyond the Ansel Adams Zone System.
Lets look at this colorful subject and examine some different approaches to creating a B+W rendition of the RGB Sunflower file.
While this is certainly not horrible it doesn’t really offer much control over the way colors are rendered into gray values. We can start to understand what’s happening here by realizing that RGB image files are made up of 3 different grayscale images. When these 3 grayscale versions are added together in RGB we end up with the full range of color as defined by the additive colorspace of our particular flavor of RGB be it sRGB, Adobe 98, ColorMatch or whatever. The default grayscale conversion utilizes a formula for blending the different grayscale channels into a single composite version.
Go to: Image>Adjustments>Channel Mixer to bring up the Channel Mixer dialog. Make sure you check the “Monochrome” check box in the lower left corner of the dialog. Now the output menu at the top of the dialog changes to “gray” and we see a grayscale version of our image that represents the red channel of the image – the “Red” slider is at 100%.
It is especially instructive to examine the other channels at 100% and note their differences in this image.
Figure 5, above & Figure 6, below] Move the sliders around enough and we can see that the default conversion is basically set up like this: 30 red, 60green, 10 blue
You will notice that the different percentages in the sliders add up to 100 and this preserves the overall luminosity of the image. We can try other percentage mixes and as long as we maintain the 100% total we should arrive at a fairly reasonable rendition.
We might prefer this version above, a 50/50 blend between green and red, because it has a slightly darker sky that lends a little more contrast to the scene. If, on the other hand, we are not looking for “reasonable’ but instead seek out “dramatic” we might want to break the 100% rule and do something like this.
By subtracting the blue channel we can arrive at an infrared look – a bit of a departure from our original color image but perhaps more compelling than the standard image.
Why stop there?
Now that we realize all rules are to be broken let’s really try to “break” this image.
These radical slider positions give us a Sabatier or “solarized” effect. We can easily see that the Channel Mixer gives us all the control (and then some) of the traditional B+W photographer’s use of color filters and specialty films.
This will “split” the RGB file into 3 separate grayscale files and name them after the channels they originated from. Using the “Move Tool” we can now drag one file on top of the other into a layer stack that we can use to blend the channels. We can re-create our first channel mixer version by dragging the green document on top of the red document (hold down the “shift” key while you do this to keep the layers registered) and change the layer opacity to 50%.
To really appreciate this approach we have to take advantage of the additional controls available in the form of layer masks and the different layer apply modes. By changing the apply mode in the green (top) layer to darken we can have the darker sky of the red layer and the darker, more detailed petals of the green layer.
This works because the darken mode only applies the pixels in the green layer that are darker than the pixels in the red layer. We can add a layer mask to protect the lighter center in the red layer from the darker one in the green layer. Lets go one step further! If we invert the blue document (Image>Adjustments>Invert) we end up with a black sky and a white flower. Drag this over our layer stack, change the apply mode to multiply and we have a result that looks similar to the channel mixer version where we subtracted the blue channel. Now, add a layer mask, apply a black to white gradient in the mask and we have this version with a nicely graduated sky.
Layer and layer masks give us very precise control over specific tonal renditions in our grayscale conversions and I think you’ll agree that this approach is worth further study.
As a final note I’d like to share a little tip for preparing B+W images for publication. All of the B+W images in this article were reproduced as CMYK files — sometimes called 4-color B+W or rich black. This is especially useful when you know that you are going to have B+W images on the same page as color images. Single channel B+W or grayscale can never look as good as 4-color reproductions simply because black ink alone, even at 100% coverage, can never be as black as the typical 280 – 300% coverage of a 4-color black. When converting grayscale images into CMYK I use a custom CMYK setup that maximizes the black ink component in order to get the best contrast and most neutral “tone” possible from the CMYK press. To create such a setup you have to go into the Color Settings dialog and change the CMYK workspace to “Custom”.
You will then be presented with the “Custom CMYK” dialog — the settings you see here are the ones I have used in a magazine publication.
You might want to experiment with different dot gain, black limit and total ink but the most critical thing to change from your standard defaults is the GCR setting. For B+W images that you’d prefer to reproduce as neutral as possible you should change the GCR from medium or light to heavy. (Note: the “maximum” setting will generate a full range “K” but nothing in the CMK channels) You might also want to change the dot gain setting for a slightly higher one because black ink tends to gain the most on press. Once you’ve made these changes click “OK” and you’ll return to the Color Settings dialog with your new CMYK “workspace” selected for you. You’re not really done, however, until you save your new “workspace” as a profile that you can recall whenever you need it. With your new custom CMYK workspace visible in the CMYK workspace area, select the CMYK workspace menu, scroll up and select “Save CMYK” this will save your CMYK setup as a profile that you can use again.
After reading Lee Varis' article, I was reminded of comments that I had heard about the improvements in CS3 for Photoshop's black and white tool for converting from color images. So I posed this question to Lee: I hear that PS3 /CS3 has a new black and white tool that is of a superior model for doing black and whites. Does that supercede your article, complement it, an alternative?
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