Digital Camera Image Scanner Color Control

Color is a fundamental aspect and complex to work with in Photoshop. A color is defined through a model , existing in a working space and turns into information through a mode. The HSB model ( Hue , Saturation and Brightness) lets us visualize and choose between colors in a wheel or cylinder of colors. The RGB model defines color, as we know, according to the proportions of red, green and blue it contains. The CMYK model uses the colors of a printing press, which are the secondary colors plus black, in equal percentages of the amount of ink used. Therefore 0% means an absence and 100% is maximum amount. The Lab model defines brightness separately and tone is expressed as a position on the red-green axis (axis a ) and blue-yellow (axis b ) which are perpendicular in the color wheel. We can choose any of these parameters to choose a color in the selector, independently of the color mode of the image.

The range of colors that are perceptible by the eye is very broad and practically coincides with the ones produced by a Lab model. On the other hand, the range that can be produced in an RGB system is much more limited. The CMYK range, which is the most restricted, includes only the colors which can be printed with the same inks. To complicate things a little more, the RGB standard mode, which is wider than the CMYK range, doesn't include all the colors of the last, since tones in green and cyan are out. In other words: not all visible colors can be registered in RGB color or printed on paper. All computers, scanners, monitors and printers are RGB devices and work in a RGB working space of smaller or greater amplitude. We can have wide spaces with many tones (including those in the CMYK range) that are only advisable for working on original destined to a printing press (for example, wide range RGB space ). Except in the case

that we are working on an original destined to a printing press, the usual is to go with the most reduced color space, which leaves out some tones in the extremes of the CMYK range, but that include all the colors that can be reflected on a monitor or TV screen, and are enough to obtain excellent results with our printer, as the RGB space . The working space is defined in the File > Color adjustments > RGB Adjustments. These are advanced adjustments, and therefore to start out it is best to pick RGB, the standard shared by most devices and operating systems.

The color mode is the way that most tones are registered in the file. In Photoshop there are four color modes and three monochrome: the RGB mode is made up of three channels of the primary colors; the CMYK mode has four channels corresponding to the inks; the Lab mode uses three channels corresponding to the brightness of the a and b axis; and finally, the indexed color mode reduces the total number of tones to 256 and is characteristic of images destined to the internet. In black and white there are three modes: grayscale, bitmap and duotone, similar to the techniques of high quality printing that uses inks of different tones of gray to reproduce shades in a black and white image. The duotone mode lets us use any color of ink to obtain a monochrome image of different tones of gray.

It's possible to convert an image from one mode to another. When we convert a color image from one mode to another of a more reduced range, there may be cases when some colors are out of range . In color the most used mode is RGB. In case we need to turn in an original on a digital support for printing we would convert it to CMYK after editing the image. In black and white the bit map mode doesn't accept some editing functions.