Details:
Summary:
At the TAGA 2007 conference in Pittsburgh the author of this paper presented a paper about color-differencing equations and the human eye. The color test was done with inexperienced observers. One of the main results was that the DE2000 equations corresponded quite well with the perceived color differences, followed closely the DECMC2:1 equation. A very similar test was carried out with experienced color observers at the IPA technical conference in Chicago in April 2008 and local print professionals in the summer of 2008. Besides having to judge a solid color chip, they were also asked to rank visual differences in four test images. As an addition to the test carried out in 2006, the DIN99 equation was also tested to see if it relates better to the perceived color differences. Interestingly the DE2000 equation related the best with how the experienced observers perceived the color differences of the solid color patches. Another question is how do any of the modern color-differencing equations relate to differences present between two similar images displayed on a computer screen. Due to the large number of new soft proofing systems being introduced into the graphic arts industry, test images were shown on a colorcalibrated display. Four ISO SCID images were chosen and modified in regards to lightness, chroma and hue. The images that were chosen varied in chroma from very colorful to mostly neutral colors. In the neutral colors all observers identified differences quite easily, but in the other images many observers had difficulties identifying slight changes in regards to lightness, but could readily identify differences in chroma and hue. Recommendation threshold values in relation to differences in lightness, chroma and hue are listed and also which of the newer colour differencing equations relates better to the perceived color differences.