An evaluation of the change in perceived image contrast with changes in displayed image size was carried out. This was achieved using data from four psychophysical investigations, which employed techniques to match the perceived contrast of displayed images of five different sizes. A total of twenty-four S-shape polynomial functions were created and applied to every original test image to produce images with different contrast levels. The objective contrast related to each function was evaluated from the gradient of the mid-section of the curve (gamma). The manipulation technique took into account published gamma differences that produced a just-noticeable-difference (JND) in perceived contrast. The filters were designed to achieve approximately half a JND, whilst keeping the mean image luminance unaltered. The processed images were then used as test series in a contrast matching experiment. Sixty-four natural scenes, with varying scene content acquired under various illumination conditions, were selected from a larger set captured for the purpose. Results showed that the degree of change in contrast between images of different sizes varied with scene content but was not as important as equivalent perceived changes in sharpness<sup> 1</sup>.
This paper proposes a visual scene busyness indicator obtained from the properties of a full spatial segmentation of static images. A fast and effective region merging scheme is applied for this purpose. It uses a semi-greedy merging criterion and an adaptive threshold to control segmentation resolution. The core of the framework is a hierarchical parallel merging model and region reduction techniques. The segmentation procedure consists of the following phases: 1. algorithmic region merging, and 2. region reduction, which includes small segment reduction and enclosed region absorption. Quantitative analyses on standard benchmark data have shown the procedure to compare favourably to other segmentation methods. Qualitative assessment of the segmentation results indicate approximate semantic correlations between segmented regions and real world objects. This characteristic is used as a basis for quantifying scene busyness in terms of properties of the segmentation map and the segmentation process that generates it. A visual busyness indicator based on full colour segmentation is evaluated against conventional measures.
In this paper an evaluation of the degree of change in the perceived image sharpness with changes in displayed image
size was carried out. This was achieved by collecting data from three psychophysical investigations that used techniques
to match the perceived sharpness of displayed images of three different sizes. The paper first describes a method
employed to create a series of frequency domain filters for sharpening and blurring. The filters were designed to achieve
one just-noticeable-difference (JND) in quality between images viewed from a certain distance and having a certain
displayed image size (and thus angle of subtense). During psychophysical experiments, the filtered images were used as
a test series for sharpness matching. For the capture of test-images, a digital SLR camera with a quality zoom lens was
used for recording natural scenes with varying scene content, under various illumination conditions. For the
psychophysical investigation, a total of sixty-four original test-images were selected and resized, using bi-cubic
interpolation, to three different image sizes, representing typical displayed sizes. Results showed that the degree of
change in sharpness between images of different sizes varied with scene content.
This paper describes an investigation of changes in image appearance when images are viewed at different image sizes
on a high-end LCD device. Two digital image capturing devices of different overall image quality were used for
recording identical natural scenes with a variety of pictorial contents. From each capturing device, a total of sixty four
captured scenes, including architecture, nature, portraits, still and moving objects and artworks under various
illumination conditions and recorded noise level were selected. The test set included some images where camera shake
was purposefully introduced. An achromatic version of the image set that contained only lightness information was
obtained by processing the captured images in CIELAB space. Rank order experiments were carried out to determine
which image attribute(s) were most affected when the displayed image size was altered. These evaluations were carried
out for both chromatic and achromatic versions of the stimuli. For the achromatic stimuli, attributes such as contrast,
brightness, sharpness and noisiness were rank-ordered by the observers in terms of the degree of change. The same
attributes, as well as hue and colourfulness, were investigated for the chromatic versions of the stimuli. Results showed
that sharpness and contrast were the two most affected attributes with changes in displayed image size. The ranking of
the remaining attributes varied with image content and illumination conditions. Further, experiments were carried out to
link original scene content to the attributes that changed mostly with changes in image size.