A Spatial Extension of CIELAB for Digital Color Image Reproduction

We describe a spatial extension to the CIELAB color metric that is useful for measuring color reproduction errors of digital images. To compute the error, digital color images are spatially filtered using a pattern-color separable method and then converted into the CIELAB representation. Over patterned regions of the image, the reproduction errors measured using the spatial extension of CIELAB correspond to perceived color errors better than errors computed without the spatial extension. Over uniform spatial regions of the image, errors computed with the extension are equal to errors computed using the standard CIELAB formulae. 2 Introduction The CIELAB system (CIE 1978) is an important international standard for measuring color reproduction errors. This system was created in a period when most color reproduction applications were concerned with matching large uniform colored areas. Hence, the CIELAB system was tested against data from color appearance judgments of large uniform field..