Monday, 11 November 2013

What is Design for Print : Colour

Colour provides dynamism to a design, attracting the attention of the viewer, and perhaps eliciting response. Colour can also be used by a designer to help organise the elements on a page and lead the eye from one item to another, or instill hierarchy.
Printing technology continues to expand the boundaries of colour reproduction, as developments such as six-colour hexachromatic printing push the colour gamut to new dimensions.

As colour is essentially different wavelengths of light, design and colour professionals use different values of hue, saturation and brightness to describe it. Importantly for designers, there are two main colour models, that relate to work on screen (RGB) and printed work (CMYK).

This diagram shows the subtractive primary colours. Each of these has one of the additive primaries missing. Where two subtractive primaries overlap, only one additive primary is visible. Blue is formed where cyan and magenta overlap. Cyan and yellow overlap to produce green. Magenta and yellow combine to form red. Where all three subtractive colours overlap, black is produced because no light escapes.

This diagram shows the additive primaries. Where red and green overlap, yellow is created. Magenta is formed where red and blue overlap, and cyan is created where blue and green overlap. These secondary colours are the subtractive primaries. Each additive primary represents a component of white light, so where all colours overlap, white is produced.

When light is present, the eye can read colour in one of three ways, reflected light, transmitted light, or a combination of reflected
and transmitted light.

Reflected Light
Reflected light is created when light from a light source, reflects off an object. The amount of light reflected depends on the surface area of the object and the brightness of the light source.

Transmitted light
Transmitted light is created when light from a light source, passes through an object. The amount of light transmitted depends on the density of the object and the brightness of the light source.

Hue, or colour, refers to the unique characteristic of a colour that helps us visually distinguish one colour from another. Hues or colours are formed by different wavelengths of light.

Saturation or chroma (chroma is another way of referring to hue, the colours formed by different wavelengths of light.) refers to the purity of a colour and saturation levels describe a colour's tendency to move towards or away from grey.

Brightness or value (value is another way of referring to brightness, how light or dark a colour is.) refers to how light or dark a colour is. Changes in the brightness value can be achieved by mixing a colour with black or white.

Hue, saturation and brightness are three colour elements that can be manipulated to change the appearance of an image. Colour manipulation of images is now relatively straightforward through the use of image-editing software, which allows a designer to easily alter the feel of a photo, as well as correct any colour problems.

The pantone PMS colour system has developed to include a wide range of different colours, including special solid, hexachrome, metallic and pastel colours.
The pantone system allocates a unique reference number to each hue and shade to facilitate communication between designers and printers.
U = Uncoated
C = Coated
EC = Euro coated
M = Matte

Spot colours;
Spot colours are made from various base element, mixed according to a specific recipe. Spot colour inks can be bought pre-mixed and ready to use or they can be created by mixing the constitute parts. For example Pantone 8001, a dull silver, not all printers stock this ink. However, as it is made from one part Panone 874, a bronze, and three parts Pantone 877, a silver, both of which most printers stock as standard, this special colour can be mixed by the printer if needed.

Colour in print;
Before sending a design to print a designer can use a range of methods to ensure that the colours used will appear as intended. When work is sent to print, it is unlikely that there will be further opportunities to rectify mistakes. For this reason, it is vital that checks are carried out on some of the most basic elements.

Preparing colour for print;
On completion, the designer must carry out a number of pre-press checks to ensure clear communication between designer, clients and printer. This is vitally important if the client is to end up with the work that they have been expecting. A designer must also review certain elements that may pose printing problems.

Checklist before printing;
  1. Delete all unused colours.
  2. Ensure all that you want to print in black is actually in black, not in registration will print in all plates.
  3. Ensure all that you should be in registration, and not in black, as black will only print on the black plate.
  4. Ensure all spot colours are accounted for. If the job is printing with a special colour, all is well; if the job is printing CMYK only, then turn all spot colours to CMYK.
  5. Ensure all images are converted to CMYK and not RGB. This includes logos, maps, additional icons, for example. In a certain circumstances the printer may prefer the files to be left in RGB for them to convert themselves to match a specific profile, but you can't assume this.
  6. Ensure you are clear that your colour-fall matches the printer's expectations. If the printer is expecting a four-colour job then supplying a file with special spot colours will cause confusion.
  7. Ensure your imported swatches are of the right value, if the job is being printing on uncoated, then set any colours as uncoated, and not coated or unspecified.
Overprinting is where one ink overprints another so that they mix to create different colours. As colour theory dictates, overprinting pairs of the three trichromatic subtractive primary process colours produces the additive primary colours. Different blacks can also be achieved with overprinting.
To overprint effectively, a designer needs to bear in mind the order in which the process colours print. If printing in the order cyan, magenta, yellow and black, the yellow obviously cannot overprint cyan, for example. Overprinting can produce creative effects when used with graphics and images.

Using tints allows a designer to increase the range of colour possibilities available when the budget for a job is insufficient to cover the cost of four-colour printing. Instead of being limited to the use of two single colours, for example, a designer still has a varied, although limited, colour palette available.
As tints are produced using half-tone dots, very light tints such as those of less than ten per cent may not reproduce well, which is why the rule of thumb minimum is ten per cent.

The four-colour printing process produces colour images from different sized half-tone dots of cyan, magenta, yellow and black ink, which combine to fool the eye into seeing a continuous-toned image.
Colour printing uses separate plates that contain half-tone dots for different printing inks. A designer can manipulate these dots in order to change the appearance of the printed image.

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