Understanding Colors and Channels Introduction In the world of design, color is one of the most important elements. When you're creating a brochure, advertisement, or banner using Adobe Photoshop, good use of color attracts the attention of the viewer. It also helps draw the elements of your design into one cohesive unit. Color is a strong motivator and is used in all aspects of our daily life. Since color is so important to design, Photoshop lets you use industry-standard color sets, or you can create and save your own customized color panels. You can also color-correct a photograph by removing the color entirely or selectively removing colors from portions of the image. In addition, Photoshop gives you ways to select areas based on color, and then fill those areas with any color you choose. Not only is it important to understand how color is used, it's also important to understand how Photoshop manages color information and that's where the Channels panel comes into the picture. Channels are where color information is stored. The number of channels in an image is based on its color mode, or color model, such as RGB (Red, Green, and Blue) or CMYK (Cyan, Magenta, Yellow, and Black). A firm understanding of channels and color modes, and their function in Photoshop, will go a long way in helping you control and manage color. When adjusting your image, you can use various commands-Auto Contrast and Color, Curves, Color Balance, Brightness/Contrast, and Desaturate, just to name a few. You can also use the Match Color and Selective Color adjustments to further fine-tune your image. Photoshop also provides a Photo Filter adjustment, as well as a Shadows and Highlights adjustment to correct those overexposed or underexposed images. With all of the commands and adjustments available, the real dilemma will be, where do you begin?
What You'll Do Work with 8-, 16-, and 32-Bit Images Work with the Channels Panel Work with Color Modes Understand the Various Color Modes Use the Replace Color Adjustment Work with the Color Panel Work with the Swatches Panel Use the Stroke and Fill Commands Create Spot Color Channels Use Auto Contrast and Auto Color Use Levels Adjustment Commands Use the Exposure Adjustment Use Curves and Color Adjustments Use Hue, Saturation, and Vibrance Use Match and Selective Color Use Channel Mixer and Gradient Map Use Photo Filter and Shadows/Highlights Use the Invert and Equalize Commands Use the Threshold and Posterize Adjustments Use the HDR Toning Adjustment Use the Black & White Adjustment
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Working with 8-, 16-, and 32-Bit Images It's all about the numbers, and that's a fact. The number of colors available for displaying or printing each pixel in an image is called bit depth-also known as pixel depth or color depth. A higher bit depth means more available colors and more accurate color representation in an image. A bit depth setting of 2 bits displays 4 colors, 4 bits displays 16 colors, 8 bits displays 256 colors, 16 bits displays 32,768 colors, and 24 bits and 32 bits both display 16.7 million colors. Most digital images currently use 8 bits of data per channel. For example, an RGB image with 8 bits per channel is capable of producing 16.7 million (a 24-bit RGB image: 8 bits x 3 channels) possible colors per pixel. While that may seem like a lot of color information, when it comes to color correction and adjustment, it isn't. In response to Photoshop users needing more control, Photoshop supports 16-bit and now 32-bit-known as High Dynamic Range
Properties
(HDR)-images. High Dynamic Range images with 32 bits per channel have a more extended dynamic range than lower bit depth images. Dynamic Range describes the ability of a channel to capture maximum information from the black to white and dark and bright areas of an image. An 8-bit channel image has a dynamic range of 250:1 (per channel), similar to the dynamic range of printed paper or a computer display. A 16-bit channel image has a dynamic range of 65,000:1, and a 32-bit channel image has a dynamic range of over 200,000:1.The greater dynamic range translates into better control over an image when making fine color and contrast adjustments using Levels and Curves (shown below). Working with HDR images is very similar to using raw files and applying exposure changes after the fact. Photographers can capture the full dynamic range of a scene with multiple exposures and merge the files into a single image.
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The ability to work with 32-bit images is relatively new in Photoshop, and initially you had a limited use of adjustments and filters. However, in Photoshop many more adjustments and filters have become available for 32-bit images, such as Hue/Saturation, Levels, Gaussian Blur, Add Noise, Smart Sharpen, Channel Mixer, and more. When adjusting the color or contrast of an image, first convert a standard 8-bit image to 16 bits, and then make your corrections. This helps prevent loss of color information, and banding between light and dark shades. Once all the color/contrast adjustments have been made, you can (if necessary) convert the image back to 8 bits. It's that simple. You can change an image's bit depth by displaying the image, clicking the Image menu, pointing to Mode, and then clicking 8 Bits/Channel, 16 Bits/Channel, or 32 Bits/Channel. When you convert a 32-bit image to 8 or 16 bits per channel, if you choose to merge your layers before changing the bit depth, Photoshop opens the HDRToning dialog box to let you make exposure and contrast corrections so the image retains the dynamic range you want. The Exposure and Gamma option lets you manually adjust brightness and contrast. Drag the Exposure slider to adjust the gain and drag the Gamma slider to adjust the contrast. The Highlight Compression option
automatically adjusts highlight values to fit within the range for 8- or 16-bit images. The Equalize Histogram option automatically preserves image contrast. The Local Adaptation option adjusts the tonality (local brightness regions) in the image. Drag the Radius slider to specify the size of the local brightness regions and then drag the Threshold slider to specify the distance between tonal values before they are included in the brightness region. If you want to reuse these settings in the future, you can save them, and then load them again as needed.
Viewi 9 32- it Im 9 The dynamic range of HDR images exceeds the display capabilities of standard monitors. When you view a 32-bit HDR image, the highlights and shadows may look dark or washed out. To correct the problem, Photoshop allows you to adjust 32-bit preview options so 32-bit images display properly on your monitor. The preview options are stored in the image file, so each file retains its own settings. To set preview options, open a 32-bit HDR image, click the View menu, and then click 32-Bit Preview Options. In the 32-bit Preview Options dialog box, select the preview settings you want (described earlier in this topic), and then click OK.
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Working with the Channels Panel
The Channels panel is Photoshop's storage locker for color and selection information. For example, when you open an RGB image, the Channels panel displays color channels of red, green, and blue. When you open a CMYK image, the color channels are cyan, magenta, yellow, and black. These primary color channels are defined as the native color channels of the image. The Channels panel can also contain spot color channels and selection masks. In addition to color information and selection masks, the Channels panel contains a composite channel. The composite, when selected, lets you view the full-calor image in the document window. Selecting any of the individual native color channels changes the active view of the image to display the selected color channel. The Channels panel stores color information using shades of gray, and each color channel is capable of displaying 256 gradations from black to white. A zero-value pixel displays as black, and a 255-value pixel displays as white. The darker the shade of gray, the less of the selected ink color is used to create the visible colors within the image.
Work with the Channels Panel
0 Open a color document.
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Click on the individual channels to view the native color channels of the active document. Click the composite channel to view the full-color image.
See Also See "Creating Spot Color Channels" on page 212 for more information on using the Channels panel. See "Using Channels to Create and Store Selections" on page 100for more information on using channels.
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Working with Color Modes Color modes define the colors represented in the active document. Although you can change the color mode of a document, it is best to select the correct color mode at the start of the project. Photoshop's color modes are Bitmap, Grayscale, Duotone, Indexed Color, RGB (Red, Green, and Blue), CMYK (Cyan, Magenta, Yellow, and Black), Lab, and Multichannel. See "Selecting Color Modes and Resolution" on page 13 for information on the best use for each color mode. The number of channels in an image depends on its color mode. For example, a CMYK image contains at least four channels, one for each color. Color modes determine the number of colors, the number of channels, and the file size of an image. For example, an RGB image has at least three channels (like a printing plate), one for red, green, and blue color information. Color modes not only define the working color space of the active document, they also represent the color space of the output document. It's the document output (print, press, or monitor) that ultimately determines the document color mode. Color modes do not just determine what colors the eye sees; they represent how the colors are mixed, and that's very important because different output devices use different color mixes. Therefore, when selecting a color mode, know the file format of the document and where it will be used. An image taken with a digital camera and then opened in Photoshop would most likely be in the RGB color mode. An image displayed on a monitor would be RGB, or possibly Indexed Color. A photograph scanned on a high-end drum scanner would most likely be in the CMYK color mode. An image being sent to a 4-color press would be CMYK, too. If you were creating a Photoshop
document from scratch, the color mode you choose should represent the eventual output destination of the document, such as on a web page, to an inkjet printer, or a 4-color press.
Switchinq Between Color Modes Unfortunately, images do not always arrive in the correct format. For example, you take several photographs with your digital (RGB) camera, but the images are being printed on a 4-color (CMYK) press, or you want to colorize a grayscale image. Changing color modes is a snap, but changing the color mode of an image isn't the problem. The problem is what happens to the digital color information when you change color modes. For example, if you open an RGB image with the intent of sending it out to a 4-color press (CMYK), the smartest course of action is to remain in the RGB color mode through the processing of the image, and then convert the image into the CMYK mode at the end. The reason has to do with how Photoshop moves between those two color spaces. For example, if you move a color-corrected CMYK image into the RGB color mode, and then back to CMYK, the colors shift because Photoshop rounds color values during the change process. On top of that, a CMYK image is 25% larger than an RGB image, and the RGB color mode represents the color space of your monitor, not a printing press. It is impossible to view subtractive CMYK color on an RGB device. If, however, the image originally came to you as a color-corrected CMYK image, then stay in and work inside that color mode.
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Understanding the RGB Color Mode
The RGB color mode is probably the most widely used of all the color modes. RGB generates color using three 8-bit channels: 1 red, 1 green, and 1 blue. Since each channel is capable of generating 256 steps of color, mathematically, that translates into 16)77,216 possible colors per image pixel. The RGB color mode (sometimes referred to as Additive RGB) is the color space of computer monitors, televisions, and any electronic display. This also includes cell phones and mobile devices. RGB is considered a device-dependent color mode. Device-dependent means that the colors in images created in the RGB color mode will appear differently on various devices. In the world of computer monitors and the web, what you see is very seldom what someone else sees; however, understanding how Photoshop manages color information goes a long way to gaining consistency over color.
Convert an Image to RGB Color
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Open an image. Click the Image menu, point to Mode, and then click RGB Color. Photoshop converts the image into the RGB color mode.
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Understanding the CMYK Calor Mode
The CMYK color mode is the color mode of paper and press. Printing presses (sometimes referred to as a 4-color press) convert an image's colors into percentages of CMYK (Cyan, Magenta, Yellow, and Black)' which eventually become the color plates on the press. One at a time, the plates apply color to a sheet of paper, and when all 4 colors have been applied, the paper contains an image similar to the CMYK image created in Photoshop. The CMYK color mode can take an image from a computer monitor to a printed document. Before converting an image into the CMYK mode, however, it's important to understand that you will lose some color saturation during the conversion. The colors that will not print are defined as being out of gamut. To view the areas of an RGB image that will lose saturation values, click the View menu, and then click Gamut Warning. Photoshop will mask all the areas of the image that are out of gamut.
Convert an Image to CMYK Color Open an image. Click the Image menu, point to Mode, and then click CMYK Color. Photoshop converts the image into the CMYK color mode.
See Also See "Using Curves and Calor Adjustments" on page 276 for more information on adjusting the calor of an image.
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Understanding the Grayscale Color Mode
The Grayscale color mode utilizes an 8-bit pixel (8 on/off light switches) to generate 1 black, 1 white, and 254 shades of gray. Although scanning and working on old black and white images might seem the obvious reason to use the Grayscale color mode, the speed and power of Photoshop, combined with faster computer systems, has prompted most photo restorers to switch to the RGB color space because of its greater versatility and ability to generate millions of colors (or shades of gray). Yet despite the move to RGB, the Grayscale color mode is still used extensively with black and white images, where file size is a consideration (grayscale images are two-thirds smaller than RGB images), and when output to rag-style papers, such as newsprint, fail to produce the detailed information available with RGB.
Convert an Image to Grayscale
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Open an image . Click the Image menu, point to Mode, and then click Grayscale. The image is automatically converted into the Grayscale color mode.
Did You Know? You can colorize a grayscale image. Convert the image into the RGBmode, and then select a color, brush, and brush size on the Options bar. The trick is to change the blending mode of the brush on the Options bar to Color. Then, as you paint on the image, the selected color will replace the original grays.
For Your Information Colorizing a Grayscale Image \
If you're planning on colorizing a grayscale image, you can increase your control of the image by creating a layer directly above the image layer, and painting in the new layer. Leave the blending mode of the brush at Normal and change the blending mode of the new layer to Color.When you paint, the color is applied and controlled in the new layer, and you have the additional option of using layer opacity to control the intensity of the effect.
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Understanding the Bitmap Calor Mode
Bitmap images consist of two colors: black and white. Bitmap images are sometimes referred to as 1-bit images. Think of a bitmap as a light switch with two positions, on and off. Each pixel in a bitmap image is either on or off, black or white. Because they are only 1 bit, the file size of a bitmap image is typically very small. Bitmap images have limited use, but often are employed for black and white ink drawings, line art, sketches, and for creating halftone screens.
Convert an Image to Bitmap
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Enter a value for Output Resolution. Click the Use list arrow, and then select from the available options: 50% Threshold. Converts pixels with gray values above the middle gray level (128) to white and below to black. The result is a high-contrast, black-and-white image.
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Pattern Dither. Converts an image by organizing the gray levels into geometric patterns of black and white dots.
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Diffusion Dither. Converts pixels with gray values above the middle gray level (128)to white and below to black using an errordiffusion process. The result is a grainy, film-like texture. Halftone Screen. Simulates the effect of printing a grayscale image through a halftone screen. Custom Pattern. Simulates the effect of printing a grayscale image through a custom halftone screen. This method lets you apply a screen texture, such as a wood grain, to an image. Click OK.
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Understanding the Indexed Calor Mode
The Indexed Color mode gives you two advantages. You can create images as small as grayscale (8-bit pixels). and you get color instead of shades of gray. Its small file size and ability to generate color make it a winning color mode for images displayed on web pages, as well as graphics used in computer-generated presentations. Its one drawback is the number of colors generated; Indexed Color images generate a maximum of 256 colors (the same number as the steps of gray in a grayscale image). The good news is that you get to choose the colors. When you convert an image into the Indexed Color mode, Photoshop creates a color lookup table (CLUT) to store the image's color information. When a color in the image cannot be found in the lookup table, Photoshop substitutes the closest available color.
Convert an Image to Indexed Color
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Open an image. Click the Image menu, point to Mode, and then click Indexed Color. Select from the following Indexed Color Mode options: • Palette. Click the list arrow to choose from the available color panels, or click Custom and create your own palette. Colors. Select the number of colors for the lookup table (3 to 256). •
Forced. Force the lookup table to hold specific colors. Black and White adds a pure black and a pure white to the color table; Primaries adds red, green, blue, cyan, magenta, yellow, black, and white; web adds the 216 web-safe colors; and Custom allows you to specify your own colors. Transparency. Select the check box to preserve transparent areas of the image (if there are no transparent areas, this option is disabled).
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Understanding the Lab Color Mode
The Lab color mode is an old color measuring system. Created in France, its purpose was to measure color based on visual perception. Since personal computers had not been created at that time, the Lab mode is not based on a particular computer or operating system, and so Lab color is device independent. The Lab mode measures color using a lightness channel, an "a" channel (red to green), and a "b" channel (blue to yellow). Lab Color works well for editing images obtained from Stock Photos, moving images between operating systems (Photoshop Mac to Photoshop Win), and for printing color images to PostScript Level 2 or 3 devices. Because of its ability to separate the gray tones of an image into an individual channel (lightness), the Lab color mode is excellent for sharpening, or increasing the contrast of an image without changing its colors. Just convert the original RGB image to Lab color, select the Lightness channel, and perform sharpening or Levels and Curves adjustments directly to the channel.
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Open an image .
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Click the Image menu, point to Mode, and then click Lab Calor. Photoshop converts the image into the Lab color mode.
Did You Know? You can use the Lab calor mode to archive RGB calor images. Since the Lab color space is deviceindependent, and RGBis devicedependent, archiving RGBimages in the Lab color mode stabilizes the image's color information and insures color accuracy, no matter what editing application is used.
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Lab color mode
Understanding the Duotone Color Mode
The Duotone Color mode converts a grayscale image into a monotone It-color), duotone (2-color). tritone (3-color). or quadtone (4-color) image using 1 to 4 custom inks. Duotones are frequently used to increase the tonal depth of a grayscale image. For example, most printing presses produce 50 levels of gray per color. By converting an image into a duotone, and using black and a mid-gray value, the press can produce a grayscale image with more dynamic range. A more common method for employing the Duotone color mode is to create an image with an overall color cast, for example, by converting the grays in the image to a sepia tone. If you're uncertain how to create the proper color mix for a duotone image, Photoshop comes equipped with dozens of sample duotone, tritone, and quadtone color presets.
Convert an Image to Duotone
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You can also save, load, or delete a preset by clicking the menu options to the right of the preset menu. Click the Type list arrow, and then select from the following options: â&#x20AC;˘ Monotone. Uses one color to generate image tone (limited dynamic range). Duotone. Uses two colors to generate image tone (better dynamic range for B&W images). Tritone. Uses three colors to generate image tone. Ouadtone. Uses four colors to generate image tone. Click the Overprint Colors button to adjust how the colors will display when the inks are printed.
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Using Multichannel Calor Mode
The Multichannel color mode is a specialized mode that converts the original color channels into shades of gray, with the grays based on the luminosity values of the original image. The original channels are converted into spot colors. Since Multichannel mode is used almost exclusively by the printing industry, converting a CMYK image into Multichannel color mode produces Cyan, Magenta, Yellow, and Black spot channels, and converting an RGB image into Multichannel mode produces Cyan, Magenta, and Yellow spot channels, minus the Black channel. In both instances, converting to Multichannel Color mode causes the loss of the Composite channel.
Use the Multichannel Calor Mode
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Open an image. Click the Image menu, point to Mode, and then click Multichannel. Photoshop converts the image into the Multichannel mode.
IMPORTANT Images converted to the Multichannel mode must be saved in the DCS 2.0 format (Desktop Calor Separations). The DCS 2.0 format generates a separate file for each of the images spot colors.
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Using the Replace Color Adjustment
Photoshop's Replace Color command lets you create a selection based on image color, and replace that color selection with any other color. The Replace Color adjustment accomplishes this by giving you access to the three components of color: Hue, Saturation, and Brightness. Hue gives you the ability to change the image's actual color, Saturation controls the amount of color, and Brightness determines how bright the color is based on its Hue and Saturation.
Use the Replace Color Adjustment Open a color document.
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Click the Image menu, point to Adjustments, and then click Replace Color.
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Select the Localized Color Clusters check box if you want to limit your color selection to a specific area on the active document, using the Selection eyedroppers to select, add, or subtract colors.
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Click the Color box to select a specific color for the selection. Drag the Fuzziness slider to increase or decrease the sensitivity of the eyedropper tools. Click the Selection or Image option to toggle between a view of the selection mask and the active image (white areas of the mask represent selected areas).
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Drag the Hue, Saturation, and Lightness sliders to change the selected areas.
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Working with the Color Panel
Photoshop not only lets you select virtually any colors you desire, it also lets you store those colors for future use. For example, you create a calor scheme for a recurring brochure and you want a way to save those colors, or you're working on an Internet graphic and you need a web-safe calor panel. Whatever your calor needs, Photoshop stands ready to meet them. The Calor panel gives you access to Photoshop's calor-generation tools. This single panel lets you create colors using 6 different sliders, 2 spectrum calor selectors, a grayscale ramp, and an option that lets you create a calor ramp for the current foreground and background colors. If you need more room to work in the Calor panel, you can resize it (New!).
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Select the Color panel. Click the Color Options button. Select from the following Calor Sliders:
Grayscale. Creates a single slider going from white (0) to black (100).
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â&#x20AC;˘ CMYK. Creates four subtractive sliders (cyan, magenta, yellow, and black). Each slider has a possible value from 0 to 100. lab. Creates three sliders (L, a, and b). The L slider has a possible value from 0 to 100, and the a, b sliders have a possible value from -128 to 127.
Web Color. Creates three sliders (red, green, and blue). Each slider has a possible hexadecimal value from 00 to FF.
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Click the Color Options button, and then select from the following Spectrums or Ramps:
Cube indicates the color is not web-safe; click to select the closest web color. An alert triangle indicates the color is out of gamut (non-printable). Color Picker (Fore round Col or)
RGB. Converts the lower
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To change a color using the Adobe Color Picker, double-click a color box, select a color using the color range or color mode options, and then click OK. You can choose colors using four color models: HSB, RGB, Lab, and CMYK.
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the Color panel to a ramp. Clicking in the ramp changes color.
To restrict the color ramp to only web-safe colors, click the Color Options button, and then click Make Ramp Web Safe.
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Current Colors. Converts the lower portion of the Color panel to a color ramp, using the current foreground and background colors. Clicking anywhere in the ramp changes the active color.
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Select options or click the color range to select a color.
For Your Information Understanding Spectrums and Ramps Spectrums and Ramps are located at the bottom of the Color panel, and represent the entire spectrum for the chosen color space. For example, the CMYK spectrum displays a rainbow of colors in the CMYK color gamut. Moving the eyedropper into the spectrum box and clicking lets you select any color and gives you a visual representation of the relationships between various colors. The Grayscale Ramp gives you linear access to the 256 available grayscale values.
Using Colors from the Kuler Panel The Kuler panel is an extension in Photoshop that allows you to use groups of color, or themes in your projects. You can use the panel to browse thousands of color themes, create your own using the complementary harmony rules, and share them with others in the Kuler community. After you find or create the theme you want, you can add it to the Swatches panel for use in your project. Click the Window menu, point to Extensions, and then click Kuler. Click the Browse tab, search for or narrow down the browse list, select the theme you want in the Kuler panel, and then click the Add Selected Theme To Swatches button to add the selected theme to the Swatches panel.
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Working with the Swatches Panel
Add a Color Swatch to the Swatches Panel
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Select the Swatches panel. Click the Swatches Options button, and then choose from the predefined color swatches. Click the Append button to add the selected color swatch to the panel.
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Select the Color panel, and then drag the sliders or enter values to create a new color swatch. Select the Swatches panel. Drag the lower right corner to expand its size beyond the range of the available colors. Move the cursor just below the last swatch color until it resembles a paint bucket. Click once, name the color, and then click OK.
Chapter 8
Photoshop not only lets you select virtually any colors you desire, it also lets you store those colors in the Swatches panel. Where the Color panel lets you select virtually any color you need, the Swatches panel lets you save and use specific colors that you use often. By default, the Swatches panel holds over 100 predefined color swatches, and has the ability to save as many user-defined swatches as you desire. You can also load saved custom swatches (ACO) or ones from HTML, CSS, or SVG files (New!), web content. If a color on a swatch is not exactly what you want or you no longer need it, you can change or delete it.