Details:
Summary:
During the June 2007 IPA Technical Conference a Proofing RoundUP was conducted and it was verified that all manufacturers could match the colors of the GRACoL Coated 1 dataset based on colorimetric measurement. The IT8.7/4 target consisting of 1617 different colors was measured with a DTP70 instrument, and color differences were determined with the Comparison Tool in X-Rite's ProfileMaker software. The test also included submissions from users, many of which also showed very similar, low differences. The criterion for evaluating the color differences was based on the delta Eab equation. The average delta delta Eab for all submitted proofs was 1.6. A visual evaluation of the proofs submitted by vendors and users was also conducted. This evaluation showed that in some instances the measured data gave the same delta Eab, but visually the proofs were rated differently. In this paper the data will be reevaluated using the color differencing equations of DE94, DE2000, and DECMC. It will be shown that it could be beneficial to use one of the aforementioned, newer color differencing equations as a criterion to rate the color accuracy of proofs. Work done in North America has focused on the use of DE94, DE2000 and DECMC, however more common in Europe is the work of the DIN and the related standards. In this paper the color differencing equation DIN99, which is specified in DIN 6176, and also in ASTM D2244-07, was used. This equation transforms the L*a*b*-color space to a more uniform color space. It applies a warping to L*, a*, b* to get L99, a99, and b99 values. This new color space is more uniform so that color differences can be computed with the normal Euclidean distance formula. The overall evaluation of the data showed that because of all the various criteria each submission had to meet using delta Eab based tolerances, these tolerances are quite rigorous to give a thorough evaluation of the provided proofs. A correlation between the visual ratings given by conference participants draws a little different picture in regards to proofs provided by suppliers and by users. For the tightly controlled vendors proofs as well as for user supplied proofs DECMC 1:1 is the color differencing equation of choice to numerical express perceived differences.