Effect of image path bit depth on image quality

Abstract

Digital Tone Reproduction Curves (TRCs) are applied to digital images for a variety of purposes including compensation for temporal engine drift, engine-to-engine color balancing, user preference, spatial nonuniformity, and gray balance. The introduction of one or more compensating TRCs can give rise to different types of image quality defects: Tonal errors occur when the printed value differs from the intended value; contours occur when the output step size is larger than the intended step size; pauses occur when two adjacent gray levels map to the same output level. Multiple-stage TRCs are implemented when compensation operations are performed independently, such as independent adjustment for temporal variation and user preference. Multiple TRCs are often implemented as independent operations to avoid complexity within an image path. The effect of each TRC cascades as an image passes through the image path. While the original image possesses given and assumed desirable quantization properties, the image passed through cascaded TRCs can possess tonal errors and gray level step sizes associated with a much lower bit-depth system. In the present study, we quantify errors (tonal errors and changes in gray-level step size) incurred by image paths with cascaded TRCs. We evaluate image paths at various bit depths. We consider real-life scenarios in which the local gray-level slope of cascaded compensating TRCs can implement an increase by as much as 200% and decrease by as much as 66%.