CIELAB HLC Colour Atlas

Transcription

1 IEAB H olour Atlas for EPSON Sureolor-Px000V Series Version 2.3en ( ) PDF with layers Default view: Proofing paper semimatte, without optical brighteners

2 Overview H-coordinates This atlas shows an overview of the part of the IEAB colour space, also known as * or simply ab, that is achievable on a high-quality inkjet printer (EPSON Sureolor-Px000V series). Instead of the orthogonal coordinates for, a and b, the IEAB polar coordinates H are used in this atlas. H is an easily understandable representation of this colour space. 36 individual tables show the division of a basic colour tone (H = ) according to brightness ( = ) and saturation ( = 10 approx. 100). Further tables show the grey axis ( = 0) and the less saturated colours ( = 5). IEAB The colour fields of the atlas are provided in the ab colour mode. The vertical -axis is the same for all colours. The horizontal position of a colour location is determined by the angle H to the positive a-axis (counterclockwise and in the unit degrees) and the radius, i. e. the distance to the -axis. H, also h or H (ab), stands for Hue (colour tone[-angle]) ightness (brightness) hroma (saturation) and is much easier to understand than the abstract a and b coordinates which do not intuitively correspond to a notion of a particular colour. Three-dimensional representation of a IEAB colour space in H partitioning. The two graphics in this column are taken from the book Digital olor Management by Jan-Peter Homann (3rd edition, Springer, 2007). The IEAB colour model was defined in 1976 by the ommission Internationale de l Eclairage. It is a mathematical colour model in which the spectral properties of an object and the perceptual properties of our visual system are offset against each other. IEAB has been established as the colour model of choice in situations where exact colour calculation is required, be it in colour measurement, colour formulation or in current operating systems: olour management usually works via IEAB. Top view of an a/b diagram of a given brightness: A IEAB colour can be specified in orthogonal coordinates for a and b as well as in polar coordinates for H and. In the exploded view, the division into Hue (angle), ightness (height) and hroma (distance from the grey axis) becomes even clearer. The pie slices correspond to the colour charts in this atlas. 2

3 Utilisation When printing is optimal, measurement of the swatches should approximately yield the same ab values as indicated for each colour swatch on the scale for the row and under the column in question. ayers for different colour spaces The PDF version of this document contains additional layers that reflect the colour gamut for further output situations. This allows comparisons, for example between papers without and with optical brighteners or between sheetfed offset and srgb (representing a standard monitor or Internet applications). The layers can be selected and deselected in Adobe Acrobat Reader or Acrobat Pro via the ayers navigation tab. Finding colours from other colour systems or the physical world You can quickly find them in the atlas by matching the original colour samples according to the intuitive system: Base colour (page) Brightness (row) Saturation (column) RGB/hex and MYK colour values can be determined in Photoshop, for example, by entering the respective colour values in the colour selector. Make sure that the correct profiles and conversion options are set in the colour settings. For example, web design hex values always refer to srgb, and MYK colour values only apply to the specific printing condition of the active colour profile. In Adobe Acrobat Professional, you can display the percentage RGB and MYK colour values of any output situation by using the Tools > Print Production > Output Preview dialogue box and pointing at the colour swatch with the mouse. The output situation is selected via its I profile from the Simulation Profile drop-down list. At freiefarbe.de you can download a digital eyedropper that shows the corresponding RGB colour values for each colour field. olour harmonies In the H model, relationships between colours such as complementary colours or harmonies can be seen at a glance. This is a great help in colour design. omplementary colours are opposite to each other in the colour circle, i.e. they have an H value that differs by the amount of 180 from each other, whereby and remain uniform. Example: Yellow (H = ) and blue (H = 270). omplementary colours therefore imply the maximum tension between two opposite poles of equal strength which cancel each other out. The brightness variation describes colours with the same H and values, whereby only the -value changes. This can be done in any number of steps. The dark-to-bright progression shows a basic colour with a gradual variation in brightness. On the other hand, the saturation variation (H and remain the same, is varied between two colours) plays with the basic statement of a hue from weak to strong. An H transition with constant angle increments and constant brightness and saturation creates a multi-coloured transition between two colours. In the opposite direction with the larger angle difference, either a larger step size results, or more intermediate colours are covered with the same angle increments. Finally, with simultaneous variation of two or three of the H parameters, many other colour harmonies can be found. In logarithmic instead of linearly graduated variations, there is a more dramatic gradation. Uneven polygons, skewed planes, screws, spirals etc. in the colour space can result in many other interesting and lively effects. For harmonic calculations, the perception-oriented and freely calculable definition of the IEAB colour space is a crucial quality advantage compared to other colour models. H H omplementary contrast: H is offset by 180, and remain the same. Brightness variation (only varies). Saturation variation (only varies). olour transition between two colours in one Hue direction. olour transition between the same two colours as above, but in the other Hue direction. 3

4 Quality assurance in the H olour System Quality assurance during production of the H olour Atlas and the spectral data derived from it for the H olour System aims at the following: very good match between olour Atlases used in different places very good match between the H olour System s spectral file and a printed H olour Atlas prerequisite for a very good match between the H olour Atlas and a digital proof (depending on the proof printer, the proof substrate, the proof software and the calibration/ profiling of the proofing system) individual quality protocol for each individual H olour Atlas In order to achieve these goals, a number of factors are intertwined that are essential for the overall quality of the product. Selection of IEAB colours for the H olour Atlas The IEAB colour space allows the description of all visible colours. However, only part of these visible colours can actually be reproduced on a printing system. Its gamut depends on the printing process, the ink used and the substrate. The H olour Atlas, the centerpiece of the H olour System, is produced on an Epson Sureolor P00V Spectro, the printer with the most precise colour reproduction of the printer market (as of June 20). Orange, violet and turquoise green complement the MYK process colours to achieve the largest possible colour space. Due to the high quality, the large colour space and the wide distribution in professional proofing, we decided to use the Epson S-P00V Spectro. The substrate for this version of the H olour Atlas is a semi-matte proofing paper without optical brighteners. process. In the design phase, it was important to make a decision for the area of saturated colours: Should only IEAB colours be included that can be reproduced 100% within the printing colour space? Should there also be very saturated ab colours, which can only be printed with slight deviations, in order to offer designers the widest possible range of colours? As part of the preparatory work for the H olour Atlas, we have decided to accept a maximum deviation of DeltaE2000 = 3 from the ideal ab value in the area of saturated colours. ontrol measurements and individual optimisation of every colour in the H olour Atlas During the design phase of this H olour Atlas (on paper without optical brighteners), all colour swatches were measured with an X-Rite i1 Pro 2 spectrophotometer and compared to the ideal ab values. As far as necessary and possible, individual colour swatches have been optimised and calibrated again for control purposes. For approx. % of the colours in the H Atlas, the ideal ab values can be reproduced with an average DeltaE2000 of 0.5. In the area of saturated colours, the deviations from the respective ideal values are somewhat higher for the reasons described above. Spectral data for the H olour Atlas During quality assu rance and production, we collected the spectral data ( nm, in 10 nm steps) of all 2040 colours in the H olour Atlas. We provide these in xf3 format free of charge in the downloads section of the freecolour.org website. Spectral data represent the most comprehensive definition of a spot colour, and they serve well as a basis for ink-formulation for different printing processes or print media, including such applications as varnishes or textiles. Reproducibility of the results arefully calibrated proofing systems enable a very good match at different points in time and across different systems at different locations. This match is in some cases even better than the match of colour guides for the graphic arts industry which are produced in other printing pro cesses. These are the basic conditions that limit the reproducible ab colours. In the actual selection of ab colours for the H olour Atlas versions, there is the general problem that some ab colours are just outside the printable colour gamut of the selected printing The rightmost swatches marked in red are the maximum saturated colours of a given colour hue in the H olour Atlas. These can deviate slightly more from their ideal H/ab value than the less saturated colours due to production tolerances. 4

5 To ensure reproducibility, we work according to the following scheme: 1. Definition of an internal reference The internal reference is the c olour gamut that the printing system must reach to output the H olour A tlas. The reference in this production is the calibration specification of the GMG olorproof software for the paper GMG ProofMedia premium semi matte 0 on Epson S-Px000V printers with violet ink. 2. onstant calibration of the proofing system The printing system for the H olour Atlas is regularly recalibrated across the entire colour space with tight tolerances. The production of the H olour Atlas will only take place when the mean deviation for all colours of the calibration chart is at DeltaE2000 < Quality documentation according to ISO :2016 The colour accuracy of each s ingle H olour Atlas is certified by freiefarbe e. V. on the last page with a quality report based on the current ISO :2016. This ISO standard describes manufacturer-independently how the achieved colour accuracy is documented on a digital proof. The central elements of quality control a ccording to ISO :2016 are the following: Standard-compliant colour wedge Output of a colour wedge that complies with ISO :2016. For the H olour Atlas, this is the Ugra/ Fogra media wedge MYK V3.0. ontrol bar for the proof job In this step, we measure and document how precisely a particular copy of the H olour Atlas matches the calibration reference defined in step 1. In our case, this reference according to ISO is not a characterisation file or an I profile of a global printing standard but a once-established characterisation, or the corresponding I profile, of the calibrated printer. Otherwise we use the normal procedure as per ISO The Ugra/Fogra media wedge for quality assurance documentation Measurement report for the Proofed Fogra Media Wedge ISO :2016 specifies a series of parameters and tolerances that must be achieved when measuring the control wedge on the proof. In the H olour Atlas, the result of this control measurement is printed next to the media wedge on the last page (see illustration above). setup for the H olour Atlas are Fogra-certified: The target values of the linearly printing Epson S-Px000V printing system on the paper GMG ProofMedia premium semimatte 0 are used as a specification for evaluation. The evaluation of the media wedge is done with a built-in X-Rite IS30 of the Epson proofing system. The result of this evaluation is printed directly beneath the media wedge. Both the Ugra/Fogra media wedge and the quality protocol can be found on the last page of the H olour A tlas as mentioned above (the licence terms of the media wedge only permit this in the printed edition of the H olour Atlas but not in the PDF). The printers and measuring devices of Proof GmbH, Tuebingen, that the H olour Atlas is produced with The proofing system used: GMG olorproof Software with Epson S-P00V Spectro The proofing paper used: GMG ProofMedia premium semimatte 0 ontract Proof reation 316 Thanks to Fogra The high quality and reproducibility that can be achieved on digital proofing systems today is closely linked to Fogra s many years of work that includes a leading role in the development of the ISO :2016 standard. Based on this and other ISO standards, Fogra offers a range of certifications for digital proofing. The following elements of the production 5

6 arge inkjet gamut The I profile Epson_P7000_ 720x1440dpi10c_GMG semimatte0_ V1.icc was used to determine the gamut for this H olour Atlas. This profile describes the following printing conditions: Printer model: EPSON Sureolor- P00V Paper: GMG ProofMedia premium semimatte 0 Resolution: 1440 dpi Driver settings for optimum colour quality The two large grey squares illustrate the entire ab value range, and the coloured area within shows the printable colour gamut at = 50. The upper chart shows the gamut of the EPSON S-Px000 printer series, whereas the chart below indicates the gamut of sheetfed offset printing on coated white papers (Fogra 39). icence This file is protected under reative ommons. It can be reproduced and passed on free of charge, even in a commercial environment, provided that the author and the licence are named freiefarbe e. V. BY-ND 4.0 icence terms This file is released under the -BY- ND 4.0 licence. The full text can be found at: IEAB is copyright-free The IEAB colour model and its polar coordinates H are free of copyrights and licensing costs as a mathematical model. Disclaimer of liability This colour atlas does not represent an exact IEAB/H reference but an approximation of the specified colour values that can be attained by means of proof printing. Despite careful preparation and multiple checks it cannot be ruled out that the present product includes errors. No liability is assumed for consequences resulting from the product s practical use. All trademarks are property of their respective owners. This product is subject to technical modifications and amendments. urrent as per February Founded in 2016, the non-profit association freiefarbe e. V. is an international association of colour professionals. We want to show: The computer is an ideal tool for colour it can make colour free! We would be pleased if you support us with a donation or become a member. Visit our website with extensive information about colour and colour communication at Authors The following persons have contributed to this olour Atlas: Matthias Betz Holger Everding Jan-Peter Homann Peter Jäger hristoph Schäfer Eric A. Soder Thanks We would like to thank olorogic GmbH, Epson Deutschland GmbH, and GMG GmbH & o. KG for their technical support, and Proof GmbH for their effort in the production of the print edition of the H olour Atlas. freiefarbe e. V. Grünteweg Oldenburg GERMANY Phone +49 (0) info@freiefarbe.de Supplier for the ring binder edition Proof GmbH Gölzstraße Tübingen GERMANY Phone +49 (0) info@proof.de shop.proof.de 6

7 H Hue colour wheel This serves the basic orientation in the atlas. For each Hue value, the outermost colour is displayed, i. e. the maximum possible saturation within the colour range of the printing system used. The angle in degrees leads you to the corresponding H colour chart in the atlas where the colour s shades are arranged according to brightness () and relative saturation (chroma, ). Utilisation When you sample a particular shade of colour, first select its base colour in the colour circle. Open the colour chart corresponding to the H angle, then look for the closest match among the colour variations. Grey axis On the following colour chart 0/ 5, the neutral colours without coloured components ( = 0) are shown to the left of the scale, and a selection of colours with low chroma ( = 5) to the right of the scale. Due to the small colour differences, the increment for H is 30 degrees in this chart. The grey axis would be leftmost in the following colour tables for H 10 to H 360, but the = 0 column is omitted because it is always the same. 7

8 0 / S-P 00V, GMG semimatte, v2.3en, (0) H

9 H 10 S-P 00V, GMG semimatte, v2.3en, H

10 H 30 S-P 00V, GMG semimatte, v2.3en, H

11 H 50 S-P 00V, GMG semimatte, v2.3en, H

12 H 70 S-P 00V, GMG semimatte, v2.3en, H

13 H S-P 00V, GMG semimatte, v2.3en, H

14 H 110 S-P 00V, GMG semimatte, v2.3en, H

15 H 130 S-P 00V, GMG semimatte, v2.3en, H

16 H 0 S-P 00V, GMG semimatte, v2.3en, H

17 H 170 S-P 00V, GMG semimatte, v2.3en, H

18 H 1 S-P 00V, GMG semimatte, v2.3en, H

19 H 210 S-P 00V, GMG semimatte, v2.3en, H

20 H 230 S-P 00V, GMG semimatte, v2.3en, H

21 H 0 S-P 00V, GMG semimatte, v2.3en, H

22 H 270 S-P 00V, GMG semimatte, v2.3en, H

23 H 2 S-P 00V, GMG semimatte, v2.3en, H

24 H 310 S-P 00V, GMG semimatte, v2.3en, H

25 H 330 S-P 00V, GMG semimatte, v2.3en, H

26 H 0 S-P 00V, GMG semimatte, v2.3en, H