This issue deals a great deal with digital color, from the basic theory to color scan or photo retouching tips. Just in time for spring when you need it most.........

     The Apple Color Picker (HLS, for Hue, Lightness, and Saturation) is based on a wheel of spectral color. The 0° point relates to pure red XXXXX. The 120° point relates to pure green XXXXX. The 240° point relates to pure blue XXXXX. These are the three additive primaries in photographic color.
     The 60° point relates to yellow XXXXX. The 180° point relates to cyan (pronounced [sigh-ann] what you might term aqua, though there are distinct differences) XXXXX. The 300° point relates to magenta (hot pink, anyone?) XXXXX. These three are the subtractive primaries of photographic color.
     To shorten these terms, red, green, and blue are expressed as R, G, B. Yellow, cyan, and magenta are termed Y, C, M. Furthermore, black is referred to a K (since B is already taken by blue). For convenience here in this article, white is W. There are two color systems based on these seven values. RGB and CMYK.
     RGB is used for monitor screens, projectors, and other places where color is created by mixing bands of spectral visible light, the spectrums being red, green, and blue in increasing frequency of the light. This is the way the eye sees, because the retinal layers are responding with the cones that are attuned to red, green, or blue bands of light. The light that comes from a source and is modified when bounced off of an object gives the impression of color to the brain. The eye only sees the three colors, and the rest are only a nuerological sensation of mixing these three basic colors. Equal levels of red, green, and blue make neutral density (black, gray, and white).
     CMYK is the "four color printing process" used by ink printing for computer printers, publication presses, photographic dye printing, etc. If you look at a magazine close up at a color image, you will see the dots of CMYK. Subtractive primaries are named such because they are colors that are missing one spectral band from white light. Yellow is "minus blue", because it is created by mixing red and green light with no blue spectrum energy present (white minus blue). Likewise, cyan is "minus red" and magenta is "minus green". The idea here is that negative images are used for printing in CMYK, and consequently, negative colors are needed to complete the process. Yellow ink is used for the blue layer in negative density.

     Assuming that all values (%) of intensity are equal, we get these formulas.

W = R+G+B
Y = R+G = W-B
C = G+B = W-R
M = R+B = W-G
R = Y+M = W-C
G = Y+C = W-M
B = C+M = W-Y

     It's a little hard to swallow at first, but this is the founding basis of all photographic and digital color. All forms of digital color are based on these principles. Some are specialized sets of predefined color, such as Pantone, which has sets of specific values to match screen and printing ink colors. But they are all based on RGB and CMYK systems. Indexed Color is a means of using RGB values to fill a palette which is then applied to an image. This is a very limited selection of colors used to decrease file size or standardize a partial set of colors (web palette) to a more manageable size or processing time frame.

The Apple RGB picker. With equal settings of 100%, the subtractive primary shows in the mix bars.





Apple CMYK mixer. Notice that the mix lines run in the reverse order and to black, instead of white as in RGB.

Biased plug for Macintosh:
     As you can see, Apple has many color calibration methods available to a wide array of applications. And to keep color correct from showing to showing, there is ColorSync. ColorSync is the system level color calibration system for equalizing the images on screen(s) and in print so that they are consistent. This helps make the RGB to CMYK transition as true to color as possible on the desktop today. This is the one reason Macintosh still survives in a Window's world, it can do color correctly and consistently. sRGB is a very lame attempt to get out of using ColorSync in Windows, while Mac still rule the desktop graphics world. This is one reason why I use Mac instead of Windows.

     Color is a matter of final presentation, and before the process begins, the designer should know the final form of display for the image. Video, web, magazine, billboard, computer slide show, photodye printing, and many other destinations have their demands on the way the color of an image is treated. Will it be broken into channels? Will it move and need consistent color throughout the multiple frames? Will it just sit there on paper and be a slave to current lighting? Will it hang on a dim wall? Will it be projected on a screen or the side of a building? Will it be on TV? Or will it sit on a web site, trying with all its might to be pretty for its highly compressed small file size? There are so many factors to color, and there is no one set of answers, only a wide array of specialties.

     Previsualization began as an art in photography, the ability to see the final image in its ultimate presentation form before the shutter is released to expose the film. In a sense, it is the ultimate in knowing the capabilities of the medium so well that they become reflexive and operate beneath conscious decision making, assuring the correct arrival at the image during an invisible phoographic process. Digital color has one step up on photography, and that is that none of the processes are invisible. Every step of the process can be seen in real time (discounting the occasional progress bar).

     Every image has its own optimal point in color balance, brightness, and contrast, when it is the best it can possibly be in terms of visual resonance for its intended presentation. This is the point of maximum emotional impact. And the art of digital color is to use the medium to achive this optimal state. RGB was designed along the mechanics of the eye to make it the easiest method to use to reach this state. This is why many of the graphics editing applications use RGB as the base mode of operation. For example, the majority of Photoshop filters operate only in RGB mode.

RGB channels: RGB, Red, Green, Blue

     RGB color is quite adaptive to screen color resolution, and the more bits used in the color setting on the monitor, the more colors there are that can be selected, making the gradients of color smoother in transition. 32 bit color is the minimal level of color for realistic presentation, as it is the first level where the mixing of tones mathematically exceeds the capabilities of the human eye to discern a color change. Most modern desktops will reach 32 bit color, but some of the older models and some laptops and some economy desktops today with only one or two meg for video output can only reach 16 bit at smaller screen sizes. At 32 bit, each channel has 8 bits (red, green, blue, and alpha), or 256 possible values (0-255). Multiplying the three color channels (256 X 256 X 256) gives 16,777,216 color combinations, commonly called millions of colors. 32 bit color, when transparency (alpha) channel is not a factor, is often called 24 bit color in professional circles. Video is one such area where the alpha channel is not a factor.

     The ability to mathematically alter the values of the channels between 0, 0, 0 (black) and 255, 255, 255 (white) allows for the control of color in an image. The patterns that are followed over the entirity of the image in these alterations define the filters and their functions. In the case of color balancing, such as correcting a faded photo for lost blue and green pigments, it's simply a matter of applying a multiplication value to every pixel color value. If the faded color only reaches 127, then multiplying every value of that channel by two will bring the maximum value up to the maximum 255. The points that had a value of 60 in that channel would then have a value of 120. Everything doubles in that channel, so its the same effect as stretching a rubber band to twice its length.

     While everything can be done mathematically as it was once done in photographic spectrography (measuring negative density under primary filtration by means of measuring light intensity transmitted through the filter and negative), digital color has an interface that allows the adjustments to be done in real time by eye. No longer is math needed for nailing it the first time, provided that the system is properly calibrated. So while the desktop handles all the basic math, the software interface allows for more subjective judgmental control.

     The easiest to nail using the interface is screen presentation RGB image, such as a JPEG. This is because the screen is the natural medium for RGB, and no further adjustments need be considered. A slide show of computer images need only made to look good on the computer on which it will be displayed. But if the images are meant for some other use or medium, then one must make settings conversions. While mathematically, RGB and CMYK are mathematically conversive, the visual equality is not linear. Because the screen is dealing with the transmission of light, and print is dealing with reflected color, the two mediums can never be perfectly linear. To be correct, there needs to be screen to ink calibrations for CMYK to work accurately and with previsualization. Professional editing software such as Photoshop, LinoColor, etc. allow for adjusted CMYK previews.

     In most cases, the starting tool for individual color selection will be HLS, the color wheel, because it shows the array of colors at once, both in terms of spectral color and saturation. This is the easiest means for selecting a desired color by eye from the full range of spectral possibilities. Simply adjust the brightness until the color is seen on the wheel, then pinpoint it with the cursor, and the desired color is defined.

     Digital color is by no means limited to these forms. To fully understand all the forms by which color can be digitally defined is a discipline for the experts. But the basic understanding of RGB is a point from which the other forms can be understood, since it is the basic form of color perception by the human eye, and its technology is that from the rest spring forth for their own individualized needs. Learn the basics of RGB and the rest can be surmised.

     For example, a simple artifact (dust spot) to repair with spot retouching.

Dust spot (simulated).




Layer in place, using eyedropper tool (option-airbrush) to measure neighboring pixels in order to obtain the color to be used for retouching. The selection is renewed every few pixels (as needed) to insure proper blending.




Close up of artifact.




Close up of repair layer (normal mode, 100% opacity, a mild Gaussian blur of 0.4 pixels)




Close up of both layers visible.




Finished retouch.

     The major advantage here is the ability to alter the repair layer easily, since there is nothing else to affect in the process of applying the touchup. If a section is applied incorrectly (we all have those days, no matter how good we get), it can be quickly erased with the eraser tool and then be re-applied, time and again, until it is satisfactory. All of this change doesn't affect the original image in the layer beneath, so there is no repairing the repairs as there can so easily be with single layer retouching.


     Now, for color balancing.

A very poorly color balanced scan (cropped section).




Color range selection to remove the worst of the magenta tint from the face.
(For those who might notice that the button is set to Image instead of Selection, my screenshot hot keys use the command key, which gives the inverse function of the radio button selection)




Selection made.




Using the color tool, I reversed the color value of the selected magenta, subtracting 180° from the HLS color angle value. This gave the complimentary green, which was then applied with the Fill command (Edit menu).




The results of flattening the layer with a 29% opacity in Color mode.




Using the highlighted hair color on the right, the selection was manually made of the hair for the fill in a new layer.




The flesh color of the skin was placed into yet another layer traced for the skin.
The results of the previous color application can be seen in the hair (Color mode, 100% opacity).




The results of the layer (Color mode, 58% opacity).




The cloning tool was used to touch up the scrape to the upper left corner of the hair, the image was flattened, and the whole image got a mild saturation boost for the finished results. Further modification to details, such as reddening the lips, varying color density, and the like can give a much more realistic effect if such detail is warranted. That is a case by case call. I would consider the results here minimal standards for a quick job.


    

Before     &     After

     The big advantage to doing localized color correction that correct tonalities (such as the bush in the background that received only minimal change) can remain proper, while the inproperly balanced colors in other areas can be adjusted as needed. Rather than struggling to find a setting that will care for the whole image, a specific solution can be sought for every different area that needs alteration. The nature of photography is not that of the human eye. It doesn't see in a curved plane, rather a flat one. It sees with chemically defined layered emulsions, not retinal cones. It has no fovia to centralize attention as the eye has. There are many areas where the camera and the eye do not agree. However, the digital process using layers can make the adjustments to film to make it see exactly as the eye experiences it, in a far easier manner than can be done photographically.

     And for change in tonal values.

The very light and drab gray sky is selected. Usually the sky has more color to the eye, but it is usually brighter than the subject by several f/stops, so it often washes out its true visual impact in photographic medium.




Layer 1 is filled with black, and the mode is set to luminosity. This will darken and even out the tonal value slightly when applied at partial opacity.




Layer 2 is filled with a sky blue and set to color. This will give the sky its blue tint, but it won't control the lightness.




With the luminosity level 1 set at 15% opacity and color level 2 set at 40% opacity gives this result, an optimal flat color.



   

Again
Before      &      After
 

     As you can see, the use of layers is an extremely important part of the retouching process. It can make or break a scan that needs a lot of attention in order to get the colors accurate. And it makes the process much more forgiving and consequently easier. Use of layers also makes it easier to standardize a group of photographs for use on the same project, as it allows for color values to be adjusted to fit the criteria. Likewise, it also allows for special effects when needed, incorporated into the process for more realistic effects. By and large, layers can not be ignored in the retouching process. They are too effective not to be used.
     So don't even think of retouching in Photoshop without first creating a new layer (or adjustment layer, if one is so inclined).