Working in Different Color Modes

The four sets of option boxes inside the Color Picker dialog box represent color models or, if you prefer, color modes (one less letter, no less meaning, perfect for you folks who are trying to cut down in life). Color models are different ways to define colors both on screen and on the printed page.

Outside the Color Picker dialog box, you can work inside any one of these color models by choosing a command from the Image>Mode submenu. In doing so, you generally change the colors in your image by dumping a few hundred, or even thousand, colors with no equivalents in the new color model.

The only exception is Lab, which in theory encompasses every unique color your eyes can detect. Rather than discuss the color models in the order in which they occur in the Mode submenu, I cover them in logical order, starting with the most common and widely accepted color model, RGB.

Also, note that I don’t discuss the duotone or multichannel modes now. Image>Mode>Duotone represents an alternative method for printing grayscale images. The multichannel mode, meanwhile, is not even a color model.

Rather, Image>Mode>Multichannel enables you to separate an image into independent channels, which you then can swap around and splice back together to create special effects.


RGB is the color model of light. RGB comprises three primary colors red, green, and blue each of which can vary between 256 levels of intensity. The RGB model is also called the additive primary model, because a color becomes lighter as you add higher levels of red, green, and blue light.

All monitors, projection devices, and other items that transmit or filter light including televisions, movie projectors, colored stage lights, and even stained glass rely on the additive primary model. Red, green, and blue light mix as follows:

  • Red and green: Full-intensity red and green mix to form yellow. Subtract some red to make chartreuse; subtract some green to make orange. All these colors assume a complete lack of blue.
  • Green and blue: Full-intensity green and blue with no red mix to form cyan. If you try hard enough, you can come up with 65,000 colors in the turquoise/jade/sky blue/sea green range.
  • Blue and red: Full-intensity blue and red mix to form magenta. Subtract some blue to make rose; subtract some red to make purple. All these colors assume a complete lack of green.
  • Red, green, and blue: Full-intensity red, green, and blue mix to form white, the absolute brightest color in the visible spectrum.
  • No light: Low intensities of red, green, and blue plunge a color into blackness. As far as image editing is concerned, the RGB color model is ideal for editing images on screen because it provides access to the entire range of 24-bit screen colors.

Furthermore, you can save an RGB image in every file format supported by Photoshop except GIF and the two DCS formats. As shown in Table below, grayscale is the only other color mode compatible with a wider range of file formats.

 Bitmap Grayscale Duotone Indexed RGB Lab CMYK
Photoshop Yes Yes Yes Yes Yes Yes Yes
BMP Yes Yes


Yes Yes



DCS 1.0 No






DCS 2.0 Yes Yes Yes*




EPS Yes Yes Yes Yes Yes Yes Yes
GIF Yes Yes











PCX Yes Yes


Yes Yes



PDF Yes Yes


Yes Yes Yes Yes
PICT Yes Yes


Yes Yes



PNG Yes** Yes


Yes Yes



Scitex CT No Yes












Table above lists color models in the order they appear in the Image>Mode submenu. Again, I left out the multichannel mode because it is not a true color model. The one exception is with duotones. Notice how I’ve included an asterisk (*) to DCS 2.0 support for duotones.

This is because you can save a duotone in DCS 2.0 only after first converting the image to the multichannel mode. For more information. As for the double asterisk with PNG in the Bitmap column: PNG supports Bitmap mode only on the Mac OS.

On the negative side, the RGB color model provides access to a wider range of colors than you can print. If you are designing an image for full-color printing, therefore, you can expect to lose many of the brightest and most vivid colors in your image.

The only way to avoid any color loss whatsoever is to have a professional scan your image to CMYK and then edit it in the CMYK mode, but then you’re working inside a limited color range. Colors can get clipped when you apply special effects, and the editing process can be exceptionally slow. The better solution is to scan your images to RGB and edit them in the Lab mode.


Back in Photoshop 2, the Modes menu provided access to the HSB hue, saturation, brightness—color model, now relegated to the Color Picker dialog box and the Color palette. Hue is pure color, the stuff rainbows are made of, measured on a 360-degree circle.

Red is located at 0 degrees, yellow at 60 degrees, green at 120 degrees, cyan at 180 degrees (midway around the circle), blue at 240 degrees, and magenta at 300 degrees. This is basically a pie-shaped version of the RGB model at full intensity.

Saturation represents the purity of the color. A zero saturation value equals gray. White, black, and any other colors you can express in a grayscale image have no saturation. Full saturation produces the purest version of a hue. Brightness is the lightness or darkness of a color. A zero brightness value equals black. Full brightness combined with full saturation results in the most vivid version of any hue.


In nature, our eyes perceive pigments according to the subtractive color model. Sunlight contains every visible color found on Earth. When sunlight is projected on an object, the object absorbs (subtracts) some of the light and reflects the rest.

The reflected light is the color you see. For example, a fire engine is bright red because it absorbs all non-red meaning all blue and green from the white-light spectrum. Pigments on a sheet of paper work the same way. You can even mix pigments to create other colors.

Suppose you paint a red brush stroke, which absorbs green and blue light, over a blue brush stroke, which absorbs green and red light. You get a blackish mess with only a modicum of blue and red light left, along with a smidgen of green because the colors weren’t absolutely pure.

But wait every child knows red and blue mix to form purple. So what gives? What gives is that what you learned in elementary school is only a rude approximation of the truth. Did you ever try mixing a vivid red with a canary yellow only to produce an ugly orange-brown glop?

The reason you didn’t achieve the bright orange you wanted is because red starts out darker than bright orange, which means you must add a great deal of yellow before you arrive at orange. And even then, the yellow had better be an incredibly bright lemon yellow, not some deep canary yellow with a lot of red in it.

Commercial Subtractive Primaries

The subtractive primary colors used by commercial printers cyan, magenta, and yellow are for the most part very light. Cyan absorbs only red light, magenta absorbs only green light, and yellow absorbs only blue light. On their own, these colors unfortunately don’t do a good job of producing dark colors. In fact, at full

intensities, cyan, magenta, and yellow all mixed together don’t get much beyond a muddy brown. That’s where black comes in. Black helps to accentuate shadows, deepen dark colors, and, of course, print real blacks. In case you’re wondering how colors mix in the CMYK model, it’s basically the opposite of the RGB model.

Because pigments are not as pure as primary colors in the additive model, though, some differences exist:

  • Cyan and magenta: Full-intensity cyan and magenta mix to form a deep blue with a little violet. Subtract some cyan to make purple; subtract some magenta to make a dull medium blue. All these colors assume a complete lack of yellow.
  • Magenta and yellow: Full-intensity magenta and yellow mix to form a brilliant red. Subtract some magenta to make vivid orange; subtract some yellow to make rose. All these colors assume a complete lack of cyan.
  • Yellow and cyan: Full-intensity yellow and cyan mix to form a bright green with a hint of blue. Subtract some yellow to make a deep teal; subtract some cyan to make chartreuse. All these colors assume a complete lack of magenta.
  • Cyan, magenta, and yellow: Full-intensity cyan, magenta, and yellow mix to form a muddy brown.
  • Black: Black pigmentation added to any other pigment darkens the color.
  • No pigment: No pigmentation results in white (assuming white is the paper color).

Editing In CMYK

If you’re used to editing RGB images, editing in the CMYK mode can require some new approaches, especially when editing individual color channels. When you view a single color channel in the RGB mode, white indicates high-intensity color, and black indicates low-intensity color.

It’s the opposite in CMYK. When you view an individual color channel, black means highintensity color, and white means low-intensity color.

This doesn’t mean RGB and CMYK color channels look like inverted versions of each other. In fact, because the color theory is inverted, they look much the same. But if you’re trying to achieve the full-intensity colors mentioned in the preceding section, you should apply black to the individual color channels, not white as you would in the RGB mode.

Should I edit in CMYK?

RGB doesn’t accurately represent the colors you get when you print an image because the RGB color space contains many colors particularly very bright colors that CMYK can’t touch. This is why when you switch from RGB to CMYK, the colors appear duller. (If you’re familiar with painting, RGB is like oils and CMYK is like acrylics. The latter lacks the depth of color provided by the former.)

For this reason, many folks advocate working exclusively in the CMYK mode, but I do not. Although working in CMYK eliminates color disappointments, it is also much slower because Photoshop has to convert CMYK values to your RGB screen on the fly.

Furthermore, your scanner and monitor are RGB devices. No matter how you work, a translation from RGB to CMYK color space must occur at some time.

If you pay the extra bucks to purchase a commercial drum scan, for example, you simply make the translation at the beginning of the process Scitex has no option but to use RGB sensors internally rather than at the end. Every color device on Earth, in fact, is RGB except the printer.

You should wait to convert to the CMYK mode until right before you print. After your artwork is finalized, choose Image>Mode>CMYK and make whatever edits you deem necessary. For example, you might want to introduce a few color corrections, apply some sharpening, and even retouch a few details by hand.

Photoshop applies your changes more slowly in the CMYK mode, but at least you’re only slowed down at the end of the job, not throughout the entire process. Before converting an image to the CMYK color space, make certain Photoshop is aware of the monitor you’re using and the printer you intend to use.

These two items can have a pronounced effect on how Photoshop generates a CMYK image. Previewing the CMYK color space While you’re editing in RGB mode, you can soft proof your image display a rough approximation of what the image will look like when converted to CMYK and printed.

Version 6 offers a few new options in this regard and changes the implementation of some old ones. To display colors in the CMYK color space, you now choose View>Proof Colors. You also can press the old CMYK preview keyboard shortcut, Ctrl+Y.

But before you do either, select the output you want to preview from the View>Proof Colors submenu. Photoshop creates the proof display based on your selection. You can preview the image using the current CMYK working space, choose Custom to specify a particular output device, or preview the individual cyan, magenta, yellow, and black plates.

The plates appear as grayscale images unless you colorize them by selecting the Color Channels in Color option in the Preferences dialog box (Ctrl+K, Ctrl+3). If you work with an older model color ink-jet printer that prints using just cyan, magenta, and yellow, you can choose the working CMY Plates option to see what your image will look like when printed without black ink.

View>Gamut Warning (Ctrl+Shift+Y) is a companion to Photoshop’s CMYK preview commands that covers so-called out-of-gamut colors RGB colors with no CMYK equivalents with gray. I find this command less useful because it demonstrates a problem without suggesting a solution.

You can desaturate the grayed colors with the sponge tool, but this accomplishes little that Photoshop won’t do automatically. A CMYK preview is much more serviceable and representative of the final CMYK image.

CIE’s Lab

RGB isn’t the only mode that responds quickly and provides a bountiful range of colors. Photoshop’s Lab color space comprises all the colors from RGB and CMYK and is every bit as fast as RGB. Many high-end users prefer to work in this mode, and I certainly advocate this if you’re brave enough.

Whereas the RGB mode is the color model of your luminescent computer screen and the CMYK mode is the color model of the reflective page, Lab is independent of light or pigment.

Perhaps you’ve already heard the bit about how, in 1931, an international color organization called the Commission Internationale d’Eclairage (CIE) developed a color model that, in theory, contains every single color the human eye can see. (Gnats, iguanas, fruit bats, go find your own color models; humans, you have CIE. Mutants and aliens maybe CIE, maybe not, too early to tell.)

Then, in 1976, the significant birthday of our nation, the CIE celebrated by coming up with two additional color systems. One of those systems was Lab, and the other was shrouded in secrecy. Well, at least I don’t know what the other one was.

Probably something that measures how, when using flash photography, the entire visible spectrum of color can bounce off your retina and come out looking the exact shade of red one normally associates with lab (not Lab) rabbits. But this is just a guess. The beauty of the Lab color model is it fills in gaps in both the RGB and CMYK models.

RGB, for example, provides an overabundance of colors in the blue-to-green range but is stingy on yellows, oranges, and other colors in the green-to-red range. Meanwhile, the colors missing from CMYK are enough to fill the holes in the Albert Hall. Lab gets everything right.

Understanding Lab anatomy

The Lab mode features three color channels, one for luminosity and two others for color ranges, known simply by the initials a and b. (The Greeks would have called them alpha and beta, if that’s any help.) Upon hearing luminosity, you might think, “Ah, just like HSL.” Well, to make things confusing, Lab’s luminosity is like HSB’s brightness. White indicates full-intensity color.

Meanwhile, the a channel contains colors ranging from deep green (low-brightness values) to gray (medium-brightness values) to vivid pink (high-brightness values). The b channel ranges from bright blue (low-brightness values) to gray to burnt yellow (high-brightness values).

As in the RGB model, these colors mix together to produce lighter colors. Only the brightness values in the luminosity channel darken the colors. So you can think of Lab as a two-channel RGB with brightness thrown on top. To get a glimpse of how it works, try the following simple experiment.

STEPS: Testing Out the Lab Mode

  1. Create a new image in the Lab mode say, 300 × 300 pixels, setting the Contents option to White.
  2. Press D to return the default colors to the Toolbox. The foreground color is now black and the background color is white.
  3. Press Ctrl+2. This takes you to the a channel.
  4. Click the gradient tool in the Toolbox. Or press Enter. In the Optionsbar, select the Foreground to Background option from the gradient pop-up menu, select the Linear gradient style, and select Normal from the Mode pop-up menu.
  5. Shift-drag with the gradient tool from the top to the bottom of the window. This creates a vertical black-to-white gradation.
  6. Press Ctrl+3. This takes you to the b channel.
  7. Shift-drag from left to right with the gradient tool. Photoshop paints a horizontal gradation.
  8. Press Ctrl+tilde (~) to return to the composite display. Now you can see all channels at once. If you’re using a 24-bit monitor, you should be looking at a window filled with an incredible array of super bright colors.

In theory, these are the brightest shades of all the colors you can see. In practice, however, the colors are limited by the display capabilities of your RGB monitor.

Using Lab

Because it’s device independent, you can use the Lab mode to edit any image. Editing in the Lab mode is as fast as editing in the RGB mode and several times faster than editing in the CMYK mode.

If you plan on printing your image to color separations, you may want to experiment with using the Lab mode instead of RGB, because Lab ensures no colors are altered when you convert the image to CMYK, except to change colors that fall outside the CMYK range.

In fact, any time you convert an image from RGB to CMYK, Photoshop automatically converts the image to the Lab mode as an intermediate step.

If you work with Photo CDs often, open the scans directly from the Photo CD format as Lab images. Kodak’s proprietary YCC color model is nearly identical to Lab, so you can expect an absolute minimum of data loss; some people claim no loss whatsoever occurs.


Grayscale is possibly my favorite color mode. Grayscale frees you from all the hassles and expense of working with color and provides access to every bit of Photoshop’s power and functionality. Anyone who says you can’t do as much with grayscale as you can with color missed out on Citizen Kane, Grapes of Wrath, Manhattan, and Raging Bull.

You can print grayscale images to any laser printer, reproduce them in any publication, and edit them on nearly any machine. Besides, they look great, they remind you of old movies, and they make a hefty book such as this one affordable. What could be better?

Other than extolling its virtues, however, there isn’t a whole lot to say about grayscale. You can convert an image to the grayscale mode regardless of its current mode, and you can convert from grayscale to any other mode just as easily.

In fact, choosing Image>Mode>Grayscale is a necessary step in converting a color image to a duotone or black-and-white bitmap.

Search your channels before converting

When you convert an image from one of the color modes to the grayscale mode, Photoshop normally weights the values of each color channel in a way that retains the apparent brightness of the overall image.

For example, when you convert an image from RGB, Photoshop weights red more heavily than blue when computing dark values. This is because red is a darker-looking color than blue (much as that might seem contrary to popular belief).

If you choose Image>Mode>Grayscale while viewing a single color channel, though, Photoshop retains all brightness values in that channel only and abandons the data in the other channels. This can be an especially useful technique for rescuing a grayscale image from a bad RGB scan.

So before switching to the grayscale mode, be sure to look at the individual color channels—particularly the red and green channels (the blue channel frequently contains substandard detail)—to see how each channel might look on its own.

To browse the channels, press Ctrl+1 for red, Ctrl+2 for green, and Ctrl+3 for blue. Or Ctrl+1 for cyan, Ctrl+2 for magenta, Ctrl+3 for yellow, and Ctrl+4 for black. Or even Ctrl+1 for luminosity, Ctrl+2 for a, and Ctrl+3 for b.

Black and white (bitmap)

Choose Image>Mode>Bitmap to convert a grayscale image to exclusively black-and-white pixels. This may sound like a boring option, but it can prove useful for gaining complete control over the printing of grayscale images.

After all, output devices, such as laser printers and imagesetters, render grayscale images as a series of tiny dots. Using the Bitmap command, you can specify the size, shape, and angle of those dots.

When you choose Image>Mode>Bitmap, Photoshop displays the Bitmap dialog box. Here you specify the resolution of the black-and-white image and select a conversion process. The options work as follows:

  • Output: Specify the resolution of the black-and-white file. If you want control over every single pixel available to your printer, raise this value to match your printer’s resolution. As a rule of thumb, try setting the Output value somewhere between 200 to 250 percent of the Input value.

  • 50% Threshold: Select this option from the Use pop-up menu to change every pixel that is darker than 50 percent gray to black and every pixel that is 50 percent gray or lighter to white.

Unless you are working toward some special effect—for example, overlaying a black-and-white version of an image over the original grayscale image—this option most likely isn’t for you. (And if you’re working toward a special effect, Image> Adjust> Threshold is the better alternative.)

  • Pattern Dither: To dither pixels is to mix them up to emulate different colors. In this case, Photoshop mixes up black and white pixels to produce shades of gray.

The Pattern Dither option dithers an image using a geometric pattern. Unfortunately, the results are pretty ugly, as demonstrated in the top example in Figure below. And the space between dots has a tendency to fill in, especially when you output to a laser printer.

  • Diffusion Dither: Select this option from the Use pop-up menu to create a mezzotint-like effect, as demonstrated in the second example in Figure above.

Again, because this option converts an image into thousands of stray pixels, you can expect your image to darken dramatically when output to a lower solution laser printer and when reproduced. So be sure to lighten the image with something like the Levels command before selecting this option.

  • Halftone Screen: When you select this option from the Use pop-up menu and press Enter, Photoshop displays the dialog box shown in Figure below.

These options enable you to apply a dot pattern to the image, as demonstrated in Figure below.

Enter the number of dots per inch in the Frequency option box and the angle of the dots in the Angle option box. Then select a dot shape from the Shape pop-up menu. Figure-8 shows examples of four shapes, each with a frequency of 24 lines per inch.

  • Custom Pattern: If you’ve defined a repeating pattern using Edit>Define Pattern, you can use it as a custom dither pattern. Figure below shows two custom examples.

I created the first pattern using the Twirl Pattern file, which is stored in the Displacement Maps folder in the Plug-Ins folder. I created the second pattern manually using the Add Noise, Emboss, and Ripple filters.

To use a custom pattern, open the Custom Pattern palette in the Bitmap dialog box. Click the icon for the pattern you want to use. If you don’t feel like creating your own patterns, use one of the preset patterns that ship with Photoshop. A number of these patterns appear by default in the palette; to access additional patterns, choose Load from the palette menu (click the right-pointing triangle in the upper-right corner of the palette to display the menu).

You can find the patterns in the Patterns folder, which lives inside the Presets folder. To delete a pattern from the palette, click its icon and choose Delete from the palette menu.

Photoshop lets you edit individual pixels in the so-called bitmap mode, but that’s about the extent of it. After you go to black-and-white, you can neither perform any serious editing nor expect to return to the grayscale mode and restore your original pixels.

So be sure to finish your image editing before choosing Image>Mode>Bitmap. Even more important, make certain to save your image before converting it to black-and-white. Frankly, saving is a good idea prior to performing any color conversion.