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Color proof

Color proofs (correct: contract proofs) are an ISO-certified test equipment for the graphic arts industry. Color proofs simulate the colorfulness of offset or gravure printing in a color and legally binding manner within the narrow tolerances of ISO 12647-7. Today, they are almost exclusively calculated using a RIP and then produced with inkjet printers on special proof papers.

The proof data is converted into separations, then reassembled into a composite image to correctly simulate overprinting and trapping. The data is then transferred as a newly created composite image to an inkjet printer, usually with more than 8 colors, which prints the data. In addition to the print data, digital proofs must also carry a UGRA/Fogra media wedge in order to be color-consistent and legally binding. Thanks to the standardised wedge, the printer is able to check the proof for correctness. Since many printing houses do not have this measuring technique at hand, the proof is often provided directly with a test report that shows the correctness of the measured values of the media wedge directly on the proof.

Earlier methods such as Chromalin etc. are no longer available on the market today.

In addition to the term “color proofs”, terms such as digital proofs, proofs or online proofs are still in common use.

ISO 12647 defines the highest standard of contract proofs, or “proofs” (ISO 12647-7), as well as the term “validation prints” (ISO 12647-8). Validation Prints are characterised by the fact that although they are less accurate in color, they can also be produced on laser printers. Compared to contract proofs, however, they accept much higher color deviations and are only legally binding after prior consultation. Real “proofs”, i.e. true contract proofs according to ISO 12647-7 are currently not only by far the best variant in terms of color but also the only legally binding proofs.

Further information:
https://en.wikipedia.org/wiki/Prepress_proofing

Colorimeter

A colour measuring device for measuring/comparing colours.
It is often used for the calibration of monitors or in biology/chemistry for analysis. More powerful devices, such as the spectrophotometer, can measure colours spectrally and are also used, among other things, for proofs to verify or calibrate printers.

Colorimetry

Colorimetry, or colour theory, is the science of colour.

It includes:

  • the perception of colour by the human eye and brain
  • the origin of colour in materials
  • the theory of colour in art
  • the physics of visible light

Colorimetry is primarily concerned with an objective and measurable evaluation and definition of colour valences (the visual perception of colour), as well as their relationships to one another.

Colour cast

When a coloured image appears as if a coloured filter is placed over it, this is called a colour cast. In printing, this is caused by a poor gray balance.

Colour depth

Specifies how many different colour shades can be displayed.
It is based on the binary system that all PCs use.
A colour depth of 1 bit would mean that 2 colours can be displayed, whereas 24 bit = 16.7 million displayable colours.

The colour depth has a direct influence on the file size.

Colour distance

The measured distance (colour difference) between two colours. The colour locations of the two colour values are displayed within a system and the difference is given in Delta-E.

Colour gamut

The colour gamut (or simply: gamut) refers to the range of all colours in a colour space that can be recognised (camera, scanner) or reproduced (printer, monitor) by a device.
It is visualised in the form of a colour solid.

Colour location

The colour location describes the position of a measured or selected colour within a colour space. This is often defined by coordinates, e.g. using L, a and b in the CIELab colour space.
The set of all the colour locations in a colour space is called the colour gamut (or gamut).

Colour management

With colour management it can be achieved that colours on different devices like cameras, scanners, monitors, laser, inkjet, offset printers and many more can be reproduced as similar as possible to each other.

Therefore device-dependent colour spaces must be used. A well working colour management will map the gamut of each device as Monitores and printer and device-independent colour spaces such as Adobe RGB 1998

Modern colour management systems use instruments such as the X-Rite i1 Pro 2 and related colour management software that creates and manages colour profiles within application programs such as the Adobe product range provides.

Colour measurement

Colour measurement is used to determine the exact colour location of a colour in a colour system.

There are three methods:

The Tristimulus Method:
A tristimulus colourimeter shines an internal light source onto the surface of the colour sample.The reflected light passes through three filters – red, green and blue – which determine the intensity of these color components.
The reflected light passes through three filters – red, green and blue – which determine the intensity of these colour components.

The Spectral Method:
A spectrophotometer works in a very similar way – but has not only three, but 31 filters that measure 31 different wavelengths of the reflected light. Thus the spectral method is one of the best methods for measuring colour.

Equality Method:
Here, a measuring device (or the eye) is used to compare the colour sample with standard colour samples until all samples are considered identical by the observer. However, this is assessed subjectively by the viewer, which is why the other methods of colour measurement are preferred in practice.

Colour mode

The colour mode is a setting that determines the depth to which colours can be displayed in an image file. This also affects the size of the file.

The most common colour modes are:

  • RGB mode (millions of colours)
  • CMYK mode (colours for four-colour printing)
  • Lab/CIELab
  • Index mode (256 colours)
  • Grayscale (256 shades)
  • Bitmap (2 colours: Black or white)

Colour model

A colour model (or colour system) is an abstract mathematical method for determining and specifying colours and their relationship to each other.
It is sometimes referred to as colour space, although the latter is the concrete application of a colour model to a colour-producing method (printer, monitor, etc.).

Well-known colour models are:

  • RGB (additive colour mixing with red, green and blue)
  • CMYK (subtractive colour mixing with cyan, magenta, yellow and black)
  • Lab/CIELab (brightness, red-green axis and blue-yellow axis)
  • HSL and HSB/HSV (Hue, Saturation, Lightness and Hue, Saturation, Brightness/Value)

Colour profile

A colour profile stores the characteristic features of a colour processing device.
These can be scanners, printers and monitors.
With the help of colour profiles it is possible to see what kind of colour range a device can represent.

Colour proof

Colour proofs (correct: contract proofs) are an ISO-certified test equipment for the graphic arts industry. Colour proofs simulate the colourfulness of offset or gravure printing in a colour and legally binding manner within the narrow tolerances of ISO 12647-7. Today, they are almost exclusively calculated using a RIP and then produced with inkjet printers on special proof papers.

The proof data is converted into separations, then reassembled into a composite image to correctly simulate overprinting and trapping. The data is then transferred as a newly created composite image to an inkjet printer, usually with more than 8 colours, which prints the data. In addition to the print data, digital proofs must also carry a UGRA/Fogra media wedge in order to be colour-consistent and legally binding. Thanks to the standardised wedge, the printer is able to check the proof for correctness. Since many printing houses do not have this measuring technique at hand, the proof is often provided directly with a test report that shows the correctness of the measured values of the media wedge directly on the proof.

Earlier methods such as Chromalin etc. are no longer available on the market today.

In addition to the term “colour proofs”, terms such as digital proofs, proofs or online proofs are still in common use.

ISO 12647 defines the highest standard of contract proofs, or “proofs” (ISO 12647-7), as well as the term “validation prints” (ISO 12647-8). Validation Prints are characterised by the fact that although they are less accurate in colour, they can also be produced on laser printers. Compared to contract proofs, however, they accept much higher colour deviations and are only legally binding after prior consultation. Real “proofs”, i.e. true contract proofs according to ISO 12647-7 are currently not only by far the best variant in terms of colour but also the only legally binding proofs.

Further information:
https://en.wikipedia.org/wiki/Prepress_proofing

Colour scale

The term “colour scale” has two meanings in the printing industry:

1. standardised printing colours (process colours) for four-colour printing (CMYK), e.g. the Euroscale.

2. proof scale: A schematic ink sample that is produced during a press proof and serves as a basis for the customer’s assessment of the printing failure and as a binding template for correct colour guidance in the production run.
In four-colour printing, for example, such a scale consists of one single print each in cyan (C), magenta (M), yellow (Y) and black (K), as well as three different combined prints in which first two, then three and then all four colours are printed together.

Colour separation

During te process of colour separation, a colourful digital image is broken down into separate colour separations according to its colour components.

Thus, for four-color printing, four monochrome images are produced, one each in cyan (C), magenta (M), yellow (Y) and black (K).

Colour space

A colour space is based on a colour model, and is its concrete application to a colouring method (printer, monitor, etc). It therefore contains all colours that can actually be represented through this method and the associated materials.

For example, sRGB and AdobeRGB are both colour spaces based on the RGB colour model. They can only represent a portion of the colours theoretically defined by the RGB model.

Colour system

A colour system (or colour model) is an abstract mathematical method for determining and specifying colours and their relationship to each other.
It is sometimes referred to as colour space, although the latter is the concrete application of a colour model to a colour-producing method (printer, monitor, etc.).

Well-known colour systems are:

  • RGB (additive colour mixing with red, green and blue)
  • CMYK (subtractive colour mixing with cyan, magenta, yellow and black)
  • Lab/CIELab (brightness, red-green axis and blue-yellow axis)
  • HSL and HSB/HSV (Hue, Saturation, Lightness and Hue, Saturation, Brightness/Value)

Colour temperature

Measured in Kelvin. The colour temperature describes the perceived colour impression of a light source.

For example, a lamp with 3000K is perceived as warm light and one with 6000K as cold light.
Our D50 standard light has a colour temperature of 5000K.

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