Since Mike Stokes started his study on the colour difference evaluation metrics on pictorial images application, more and more researches in this field were investigated recently. The CIE TC 8-02 is devoted to study, develop and standardise methods to derive colour difference for images. In it's latest meeting, it is agreed that a set of test images will be produced based upon the JIS/SCID and SHIPP images. This study is associated with this purpose and color difference thresholds were invested for printed pictorial images. Seven transforms were applied to the standard images. They are: sigmoidal compression in L~*., power compression in L~*, power compression in C~*, linear compression in C~*, hue angle shift, power compression in both L~* and C~*, and linear compression in L~* and C~*. The effects of transforms were assessed by a panel of observers. The results were used to develop the perceptibility and acceptability for each transform. The thresholds were expressed colorimetricly using pixel by pixel comparisons between the test images and standard image using CIELAB color difference formula. In general, if the average ΔE between two images is greater than 2.5, the colour difference can be seen by the observers. The acceptability thresholds vary according to the image's content and the transform being used.
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