Delta E
Delta E - often also dE or ∆E or ∆E76 - is a measure for the distance between two colors. When specifying color differences according to the ΔE-formal, the value 1 denotes a distance that the human eye no longer perceives.
∆E94 and ∆E00 are the most common successor formulas, which approach a visual equidistance better by partly very complicated modifications of the CIELAB colour distance formula.
The value of Delta E between the color coordinates (L*,a*,b*)p and (L*,a*,b*)v is calculated for ∆E76 as follows:
Figure 1: The formula for calculating the chromaticity for ∆E76
The result of the calculation is a value that indicates to what extent two color values - an initial color value and a measured color value - differ from each other. The following table shows what the individual numbers say.
| ∆E |
Interpretation |
|---|---|
| 0,0 to 0,5 |
almost imperceptible |
| 0,5 to 1,0 |
noticeable to the trained eye |
| 1,0 to 2.0 |
minimum color differences |
| 2,0 to 4,0 |
distinct color differences |
| 4,0 to 5.0 |
significant, generally unacceptable color differences |
| 5.0 or more |
the differences are evaluated as another color completely |
Device Link Profile
DeviceLink profiles represent a special type of profile in the color management environment. DeviceLink profiles complete the color conversion of »normal« ICC output profiles and are often used for special applications to achieve significantly better results.
DeviceLink profiles have some advantages over the usual ICC-based device profiles:
- DeviceLink profiles map a direct conversion between input and output color space. Color values or color combinations can be protected or specifically adapted and are only changed where necessary.
- DeviceLink profiles compensate for numerous weaknesses that can occur during conversion with ICC output profiles. For example, DeviceLink links can be used to preserve the black channel, so that the font is only printed in black and not in four colors.
- In addition, printing ink can be saved (SaveInk) and the result can be adapted to the paper color.
- During proofing, DeviceLinks can also significantly improve proof quality if they are iterated.
In the Workflow, DeviceLink profiles are used for all combinations of color spaces – gray, RGB, CMYK and multicolor. The most important applications are probably the conversion of CMYK to CMYK, RGB to CMYK and CMYK to multicolor as well as multicolor to multicolor.
DeviceN-Color Space
Since PostScript 3 and PDF 1.3 the DeviceN color space is supported, which allows arbitrary combinations of color channels when defining colors. Examples are:
- Pantone® Hexachrome™ – six-channel color system
- CMYK and two Spot Colors – CMYK in combination with a pantone color definition and an overprinting white
- Black and one Spot Color – Black with varnish
Without the DeviceN color space, images with such combinations could not be displayed in composite PostScript and PDF, but only with CMYK as an approximation. DeviceN color spaces can be used for both composite printing and in-RIP separation.
The advantage of the DeviceN color space is that many more color combinations with Spot Colors are possible in composite printing. These come into their own when the output device has physically separated color channels.
However, DeviceN color definitions can also have disadvantages. These include:
- Older RIP versions do not yet support DeviceN, which is why print jobs containing objects in the DeviceN color space are terminated with a PostScript error on such devices. In the case of Workflow, these color spaces are of course processed in conjunction with Global Graphics' HHR-RIP without any problems.
- DeviceN color spaces are often used to output Spot Colors, but CMYK printers and proof printers cannot correctly map Spot Colors. In the case of Workflow, Spot Colors in CMYK or CMYK with gamma-expanding colors are converted into the output color space via the color calculation with the smallest possible color distance (DeltaE).
- Extraction of individual color values at PDF level is not supported throughout. If, for example, the cutting die that lies above a green CMYK area was created in DeviceN with the values 70/0/70/0/100, the cutting contour cannot be deleted or changed with Adobe Illustrator and the cutting contour cannot be extracted or deleted because individual color values from DeviceN constructs cannot be removed so easily. In the case of Workflow, the DeviceN Colors correction profile is available for precisely this problem.
Downsampling
In addition to data compression, downsampling is another very efficient way of saving storage space. In contrast to compression, downsampling always involves losses and can therefore only be used to a very limited extent. It is not possible to make a general statement as to whether the reduction of storage space - without visible loss of quality - through lossy compression or through downsampling is preferable. Too often, environmental conditions have to be taken into account when making this decision.
In most cases, there is no need to "downsample" data in prepress in internal workflows, but a reduction can have a significant impact on the processing speed in workflow or PDF editors. The transport of data from an agency to the service office or to cloud services can also be accelerated enormously as a result. However, the user must always be aware of one thing: Downsampling in conjunction with lossy compression very quickly leads to unsatisfactory results.
The way in which downsampling algorithms work makes a huge difference to the quality of the data to be reproduced. Downsampling converts the effective resolution into a new output resolution. The method of data reduction determines the process (algorithm) for downsampling pixel information. The two best-known algorithms for recalculation in addition to short calculation are:
Average Downsampling
The value of a specific pixel is not used here as in the short calculation, but the average value - resulting from the values of all combined pixels - is calculated (averaged).
Functioning: The average value of the pixels within the 2 x 2 or 3 x 3 matrix is determined and an average tone is reproduced using a larger pixel. The example in Figure 1 shows how this works, but the limitations are also clearly recognizable here - when calculating at 200 dpi.
Figure 1: Schematic representation of the average recalculation from 600 to 200 or 300 ppi
When upsampling images, this is referred to as the bilinear approach. Newly added pixels are given the color tone that was calculated by averaging the color values of the neighboring pixels.
Bicubic Downsampling
This is also a procedure in which mean values are formed by downsampling. However, in contrast to Average Downsampling, the mean value is weighted. The weighting of the mean value depends on the pixel values surrounding the matrix. This results in even less loss of quality. This means that the tone value of the target pixel is made slightly brighter than the average of the pixels would result if there were brighter pixels in the surrounding area.
When upsampling, the bicubic method leads to softer tonal gradations through complex calculations.
DPI/LPI
The measure of resolution is usually given as the number of pixels, lines or dots per centimeter or Inch The input is usually in dpi (dots per inch) and the output in lpi (lines per inch).
Drop Zone
A design element used in the user interface to upload documents into the Workflow.
Drag and drop a compatible print document into the drop-zone [4] or click with the mouse to open a file selection dialog [5].
Figure 1: The drop zone "Upload Files" [1] in the dialog "Create Order" can be opened via Order > + New List > Print Item.
The file is only transferred to the server when the Order (or Order Item) is created.
Figure 2: The drop-zone for creating an Article or a Collection [2] can be found in the Article list.
Drag one or more files to this area. The upload starts immediately after releasing the mouse button.
Durst
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