The color model is an abstract mathematical model describing an approach to represent colors by tuples of numbers such as RGB or CMYK Kaur Sahib 2015. Color space is a specific organization of colors. Each specific color model can have different color spaces. Color space is represented in a three-dimensional coordinate system. In the three dimensional systems, each color is represented by a single point. To apply color as a visual cue in computer vision applications image processing and multimedia an appropriate approach to represent the signal of color is required. Color space provides a reasonable approach to recognize order affect and effectively display the colors of the object taken into consideration. The problem’s declaration and solution can be addressed by choosing a suitable color model. The knowledge about the way color signals generated and what information needed from the color signal is important during the color model selection process.
There are several usages of the color model such as identify the categories of color for a number of application judging the similarity and discriminate between colors and define the colors. Color models can be categorized into three categories, the device-dependent color model, user-oriented color models, and device-independent color models. Device dependent color models are also known as device-oriented color model. The resulting colors depend on the device used to display it. The different devices will produce different colors for the same original. Device dependent color spaces are widely applied in the application that require consistency between the color and the hardware device. User-oriented color models work as a connection between the human operator and the device used to handle the color information. It is experimental approximate to the human color perception Kelda Kaur 2014. It enables human operators to express and describe the perception of the colors. Device-independent color models is opposite to the device-dependent color model. As the name suggested the resulting color does not depends on the device used to display the color. The characteristic of the device does not affect the color produced. This type of color space is used in the color management system.
The color management system can eliminate or at least reduce the color difference between device Enfocus BVBA 2011. RGB color model is an additive color model that produces a wide range of colors by mixing up red light green light and blue light in a various ways Anderson Krogh 2015 Kaur Sahib 2015 Skrede 2017. The color components in RGB color model are red green and blue. Secondary color such as cyan magenta and yellow can be produced by adding up two of the primary colors in the RGB model as shown in Figure 5. It is based on the Cartesian coordinate system and organized in a unit cube as shown in Figure 6. Colors in RGB color model are represented in coordinates r g b. The values of red r green g and blue b range from 0 to 255 RGB color model is commonly used in an electronic system such as computers and television RGB is a device-dependent color model. The different devices will generate different RGB values for the same original. Even two devices with the same brand and model will also produce different RGB values for the same original. This is because the character and properties of the hardware components of every device is not exactly the same. A slightly different can affect the resulting color for RGB color model The typical devices that will produce RGB images are image scanners video cameras and digital cameras.
Devices such as television, computer, monitor video, projectors, multicolor LED displays and the mobile screen will display RGB color, However, color printers are not RGB devices. Color spaces such as sRGB and Adobe RGB are belonged to RGB color model Figure 5 RGB color model Figure 6 CMYK color model CMYK color model is a subtractive color model which based on subtracting light Anderson Krogh 2015. It is the reverse model of RGB color model Jeon Lee 2013 CMYK is used for color printing purpose. The name of the model comes from color components cyan, magenta, yellow and black. Cyan yellow and magenta are secondary colors made up by combining two primary colors as shown in Figure 5. Primary colors red green and blue can be produced by adding the two color components of CMYK color model as shown in Figure 6. All type of image file will be converted to CMYK in order to print. The CMYK is the machine-understandable instruction for a device. The device will print out the image according to the instruction given CMYK is a device-dependent color model which means that the resulting color will depend on the devices used.
The characteristic of the printer ink and the paper will affect the appearance of the color. The same image printed using different printer will have different output. The white light that reflects back from the paper will be filtered by the CMYK inks. Some of the red, green and blue light from the spectrum will be subtracted Enfocus BVBA 2011b CIE stands for Commission Internationale de l Eclairage International Commission on Illumination All CIE color models are device-independent. A color specified by one of the CIE systems will remain the same for any user anywhere Lukac N Plataniotis 2007. Colors are characterized by the luminance parameter and two-color coordinates in the CIE system. One of the most useful color spaces of CIE systems is CIELAB color space. It is designed to approximate human vision perception Anderson Krogh 2015. It is an improved version of CIEXYZ color space. The colorimetric difference between colors in CIEXYZ do not match with the color difference perceived by human CIELAB was developed to solve this issue CIELAB color space consist of three channels.