CMYK is shorthand for the colors cyan, magenta, yellow and key line black, each letter is pronounced separately. They are known together as the four color process or simply process color. CMYK works by chemically mixing the four colors together and by doing this it allows almost any color in the spectrum to be achieved.
This color model is worldwide and predominantly used the most in modern day industry offset printing (lithography). This print process works on a very simple principle, thank ink and water do not mix.
The images or text are put on plates, and each color has its own separate plate. These are first dampened by water then the colored by the ink, as a result the ink sticks to where the text and image is and the water to the area surrounding it. This image is then transferred to a rubber blanket on a roller and then finally onto paper. Hence it is called ‘offset’ as the image never goes directly onto the paper.
Each color plate is then printed precisely on top of one another on the paper to allow the colors to combine and build up the layers to form the final full color image. Cyan is the first plate and color to be printed then magenta, yellow and finally black which gives the extra details and deeper tones within the final image.
Black is added to the process as the black produced my mixing only CMY primaries will only give a dark muddy brown. Also using 100% CMY in the areas which is needed t produce black will build up and because of their concentration bleed and the image could loose sharp edges especially in text, and simply providing a black ink is cheaper.
The CMYK model works by using tiny drops of pigment (also known as halftones or screening), which allows less than the full saturation of the CMY primary colors. These tiny dots of ink are too small for the human eye to see on its own so when we look at an image we cannot see the overlapping dots, and we see just one color. Without using this process we would only be able to produce six colors; Cyan, magenta, yellow and their complentory color red, green and blue. So halftone gives us a full continuous range of color to work from.
CMYK is known as a subtractive process as it partially or fully masks certain colors. It takes away the natural light and white pigment of the paper, and means the more ink on the paper the darker the image will be.
One of the other predominate used screen based color systems is RGB. This color model has a much wider gamut and as result has much brighter, vivid colors. It is an additive color space as the more light on screen, the brighter the image will be. This is why for CMYK it is hard to match some colors produced by RBG, because it has a much smaller gamut. Though it puts up a good fight and does its best.
RGB
Apart from CMYK the other main way to mix colour in the design world is using the RGB colour model.
Its stands for the primary colours of light Red, Green and Blue, used to produce all on screen colours for the display of images in electronic systems, for example televisions, computers and mobile phones.
It is an additive colour model in which each colour, Red, Green and Blue light are added together in a variety of ways and intensity’s from being fully on or fully off in order to produce wide colour spectrum. The basic principle is, the more light there is on screen the brighter and vivid the RGB colour will be.
Changing the Hue and Saturation in two of the three colour channels it results in making one of secondary colours in CMY. For example, Cyan is made by mixing Green + Blue of equal intensity, Magenta is made by Red + Blue and Yellow is made by Red + blue. Each Secondary colour is the compliment of one primary colour (RGB), when a primary is mixed with its complimentary secondary colour, then white is produced.
However RGB’s colour’s is device dependant, which means different devices will recreate a given RGB value differently, leading to a change in colour matches. So a RGB value is not the same across devices and you should not expect the same result unless there is a form of colour management, which will try, and balance/match the RGB value.
This causes a problem when it comes to printing, as it is an additive colour space is means it has a much larger gamut than CMYK and most inkjet and laser printers print in this colour mode.
There is no simple or easy conversion to change the colours apart from using a colour management system that is mentioned above. It results in most colours printed becoming darker, though some can be closely matched in CMYK. Another reason to explain why the colours differ when converting RGB into CMYK is that, on screen RGB uses pixels per inch (these are tiny and millions can be packed into one single inch). Where as CMYK prints in dots per inch, these are a considerably bigger resulting in reducing detail and the brightness of colour.
Spot Colour
A spot colour is any colour that can be printed in a single run. They are printed using offset printers, and the colours can be any colour, mixed or pure. Predominantly offset printing uses process colour, which are Cyan, Magenta, Yellow and Black to produce the final image normally where continuous tones (as in photographs) are required. However it can also use pre mixed inks, which within the industry are known as the true spot colours. Any colour generated by non-standard offset printer ink is one, for example; fluorescent colours, metallic and even glitter colours. As the inks are specially pre mixed it allows colours to be printed out at any time and out of the CMYK gamut range. A lot of these colours have much higher vibrancy and hard to replicate without using spot colours.
The standard industry-referencing guide to spot colours is Pantone®. It is the main company in the UK for digitizing and colour matching spot colours, with over 1000 swatches available. It allows each colour to have a name and serial number, so once typed in you have the exact same ink colour, as it is ready-mixed to produce a particular colour.
Duotones
A duotone is an image of a continuous tone, printed in only two colours/spot colours. These colours can be absolutely any colour and the duotone effect is made by separate greyscales of the different colour tones combined. It was traditionally used in photography before digital came along to make the black and white prints more exciting and have more of a visual impact –using sepia tones (muddy brown/copper colours) and blueprint tones (deep blue tones).
However in this digital age duotones are now used to create an eye catching more textured piece. This is aided by changing the hue and saturation on one or both colour – making the tones within the image brighter almost till it is hard to look at or till the image is very subtle and sophisticated.
Duotone printing only uses two plates, one for each colour. So as a result is much cheaper to print than a standard process colour in offset printing, which uses four. This could work for your advantage and save a lot of money.
Greyscale
Greyscale images hold the continuous tones of black and white and any colour in-between. A grey scale is distinctly different form black and white images, which only use two colours in them: black and white, these are particularly used in gaming imagery.
A digital greyscale image has set values/weights of colour within the greyscale range depending on the luminously of the image. These range from 0% being black to 100%, which is pure white. When converting a colour image to greyscale, the computer try’s to match the values to the luminously of the colour image using the RGB channels and converts them into there equivalent shade of grey. Some greyscale images are also know as monochromatic, these are images of neutral colours and their colour range only consists of one single colour.
Monotone
A monotone image only uses a single colour in it and the any tones of that colour. You can vary the intensity of the colour and tones by altering the hue and saturation within the image. Also depending on what stock you chose to print on –this will also alter the single colour and printed tones. Monochrome printing goes way back to the early century’s when it was very popular – artists used to paint with black or brown inks and dilute them to get the shades in between to paint realistic monotone pictures.
It is less used today as the digital age has sweep over but it is still popular within wet photography, using tones such a sepia and blueprint tones to create the monotone effect.
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