Progressive transmission of pseudo-color images. Appendix 1: Item 4

The transmission of digital images can require considerable channel bandwidth. The cost of obtaining such a channel can be prohibitive, or the channel might simply not be available. In this case, progressive transmission (PT) can be useful. PT presents the user with a coarse initial image approximation, and then proceeds to refine it. In this way, the user tends to receive information about the content of the image sooner than if a sequential transmission method is used. PT finds application in image data base browsing, teleconferencing, medical and other applications. A PT scheme is developed for use with a particular type of image data, the pseudo-color or color mapped image. Such images consist of a table of colors called a colormap, plus a 2-D array of index values which indicate which colormap entry is to be used to display a given pixel. This type of image presents some unique problems for a PT coder, and techniques for overcoming these problems are developed. A computer simulation of the color mapped PT scheme is developed to evaluate its performance. Results of simulation using several test images are presented

Preferences and tolerances in color image reproduction

Observer preferences in the color reproduction of pictorial images have been a topic of debate for many years. Through a series of three psychophysical experiments we are trying to better understand the differences and trends in observer preferences for pictorial images, determine if cultural biases on preference exist, and finally generate a set of preferred color reproduced images for future experimentation and evaluation. The first experiment was a survey of observers rating the importance of commonly used image characteristics terms in correlation to color image quality. The data collected demonstrated that observer preferences remain relatively constant while judging color attributes between different media and for various image content. Experiment I also aided in the decision to utilize five dimensions of manipulation to generate preferred color reproductions, for Experiments II and in. The dimensions were, lightness (gamma adjustment to L*), contrast (sigmoid adjustment to L*), chroma (multiplicative factor on Cab* at a given hab), hue rotation, and color balance (additive adjustments to a* and b*). The second experiment was a rank order of image preference conducted at several research facilities around the world. The results yielded that statistical difference between peak preferences of image quality between cultures may exist but that the cultural difference is most likely not of practical significance for most applications. Furthermore, the shape of the preference curves across cultures is very similar so any cultural bias present is small. The final experiment was an adjustment experiment, in which observers were asked to generate the most preferred image possible. The observer variability (inter-observers) and repeatability (intra-observer) in generating preferred images were analyzed. The analysis of Experiment HI yielded that the intra-observer repeatability of an observer is about half of the variation between observers. Furthermore the analysis demonstrated that preferences on images with faces have a much tighter range of preference in comparison to images without faces. Finally, a cross analysis of Experiment II and HI was completed by the generation of preferred image sets from the results of the two experiments. The resultant images proved to be a good visualization of the range of variability in making preferred images from the color dimensions provided, and also visually demonstrated that the two techniques, (making one color adjustment at a time verses compounding color adjustments) of generating preferred images result in similar solutions

Preferred color correction for mixed taking-illuminant placement and cropping

The growth of automatic layout capabilities for publications such as photo books and image sharing websites enables consumers to create personalized presentations without much experience or the use of professional page design software. Automated color correction of images has been well studied over the years, but the methodology for determining how to correct images has almost exclusively considered images as independent indivisible objects. In modern documents, such as photo books or web sharing sites, images are automatically placed on pages in juxtaposition to others and some images are automatically cropped. Understanding how color correction preferences are impacted by complex arrangements has become important. A small number of photographs taken under a variety illumination conditions were presented to observers both individually and in combinations. Cropped and uncropped versions of the shots were included. Users had opportunities to set preferred color balance and chroma for the images within the experiment. Analyses point toward trends indicating a preference for higher chroma for most cropped images in comparison to settings for the full spatial extent images. It is also shown that observers make different color balance choices when correcting an image in isolation versus when correcting the same image in the presence of a second shot taken under a different illuminant. Across 84 responses, approximately 60% showed the tendency to choose image white points that were further from the display white point when multiple images from different taking illuminants were simultaneously presented versus when the images were adjusted in isolation on the same display. Observers were also shown to preserve the relative white point bias of the original taking illuminants