Photoshop Filter and Tool Tutorials
All Tutorial Text & Images - Copyright © 2011 KHI, Inc.
Using the Photoshop Color Picker
The Photoshop "Color Picker" palette window allows you to select a color by sampling a "Foreground Color" from an existing image using the "Eyedropper Tool" (I) located in the Photoshop Tool palette. It also provides a visual reference to the entire tonal spectrum of a given hue (color) from lightest to darkest, and from least saturated to most saturated. It also provides a numeric value for each color in RGB, Hexadecimal and LAB or percentage values in the CMYK color-space.
Once you have sampled the desired color you can find that color's RGB, CMYK, or Web Palette "Hexadecimal" (#) color formulas and equivalents. You can also manually enter CMYK percentages and Hexadecimal or RGB values and your selection will be displayed in the "Select Foreground Color" viewing box located in the Photoshop Tool palette. By checking the "Only Web Colors" radio button it will force the picker to display only the 256 "web safe" colors. It will also provide an "out-of-gamut" warning for a CMYK image.
Technical Note: You can set the sensitivity of the Eyedropper Tool by setting the "Sample Size" to "Point Sample," "3 by 3 Average," or "5 by 5 Average" in the tool bar. If you are sampling from a photo with a lot of noise, use the "3 by 3 Average" setting to simulate (average) the perceived color.
RGB Additive & CMYK Subtractive Color
The diagram above illustrates the difference between Additive Color (RGB or "Red, Green, Blue") Fig. 1, and Subtractive Color (CMYK or Cyan, Magenta, Yellow, Black) Fig. 2. When you combine Red, Green, and Blue in the Additive Color process, the combination produces white. In the Additive Color process, white is the combination of all colors. In the Subtractive Color (CMYK) process, when you combine Yellow, Cyan, and Magenta (CMY), the combination produces black. In the Subtractive Color process, black is the combination of all colors.
The diagram above illustrates the difference between Additive Color (RGB or "Red, Green, Blue") Fig. 1, and Subtractive Color (CMYK or Cyan, Magenta, Yellow, Black) Fig. 2. When you combine Red, Green, and Blue in the Additive Color process, the combination produces white. In the Additive Color process, white is the combination of all colors. In the Subtractive Color (CMYK) process, when you combine Yellow, Cyan, and Magenta (CMY), the combination produces black. In the Subtractive Color process, black is the combination of all colors. RGB equivalents are expressed in numeric values from 0 to 255. An RGB numeric value of "0, 0, 0" creates a solid black, while a numeric value of "255, 255, 255" creates pure white.
Hexadecimal Web Color Equivalent
A hexadecimal color value, or "hex triplet" is a six-digit, three-byte numeric code number used in HTML web page code and CSS style sheet code. The bytes represent red, green, or blue components in a given color. In the hexadecimal system (hexadecimal notation), numbers in the range 00 to FF are used, as opposed to 0 to 255 in RGB decimal notation.
R/16 = x + y/16
To calculate a hexadecimal equivalent for RGB, you would divide each three digit number by sixteen (ignoring any remainder) to obtain the first hexadecimal digit. Letters ranging from A to F will represent numbers 10 to 15. The second digit in each two digit number is obtained by multiplying the remainder by 16.
Lab Color Space
Based on the Munsell color system, the Lab color space, which is an abbreviation for CIE 1976 (L*, a*, b*), or CIELAB is designed to approximate human vision, with the dimension "L" representing luminance and "a" or "b" representing the Red/Green" and "Yellow/Blue" color-opponent dimensions. Some of the colors contained within the Lab color space fall outside the gamut of human vision, and requires more data per pixel than a CMYK or RGB file.
HSB Color Space
The HSB color space, also known as the HSL (hue, saturation, lightness) or HSV (hue, saturation, value) color space, identifies colors as points within a cylinder. The cylinder's central axis ranges from black at the bottom to white at the top with neutral shades of grey in between. Moving from the central axis towards the outer edge of the cylinder represents increasing saturation, and hue changes occur along the outer diameter. In the Photoshop "General Preferences" window you can set the Color Picker to "Adobe" or use your computer's default color scale.
Photoshop Eyedropper Tool
If you need to know the numeric value of a specific color you would use Photoshop's "Color Picker" window to sample colors (using the 'Eyedropper Tool') and read their corresponding hexadecimal color values, RGB color values, or CMYK color values. If you are printing the image you will need to make sure that extremely saturated colors are not "out-of-gamut." Colors that may be visible on an RGB monitor or contained in an RGB file are not possible to print due to the limitations of the printing press and the "subtractive" color process.
If a sampled color is out-of-gamut you will see a small warning triangle (above) which you can then click to see what the closest approximation would be if you were to convert the RGB file to CMYK. You will notice that most of the extreme right side of the color box is out-of-gamut and therefor, cannot be reproduced on a printing press. Reds are the most problematic color to approximate on a 4-color printing press.
Color-Sampling with the Photoshop 'Eyedropper Tool'
If you are retouching a certain area with the Paint Brush Tool, you can use Photoshop's 'Eyedropper Tool' (I) to sample a color from the surrounding area. If you are retouching a large gradated area you will want to set your brush value to a lower opacity and resample in the lighter and darker areas of the tonal gradation.
If the photograph you are working on has a high noise level you will want to set the Eyedropper's "Sample Size" from the default setting of 'Point Sample' to a higher value of '3 by 3 Average,' or even '5 by 5 Average.' This will select the average color value over a wide pixel area, avoiding the odd results from sampling a noise pixel that does not reflect the overall area color. If you are going to use the sampled color over a long period, save the color to your "Swatches" palette window.
Note: The following hardware and software was used in this tutorial: An Apple Mac Pro desktop computer, a Wacom Intuos 6x8 drawing tablet, Adobe Photoshop CS-CS5 photo editing software and a properly calibrated monitor.
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