This article explains the cause of the color fringing phenomenon that can be noticed in photographs, particularly on the edges of backlit objects. The nature of color fringing is optical, and particularly related to the difference of blur spots at different wavelengths. Therefore color fringing can be observed both in digital and silver halide photography. The hypothesis that lateral chromatic aberration is the only cause of color fringing is discarded. The factors that can influence the intensity of color fringing are carefully studied, some of them being specific to digital photography. A protocol to measure color fringing with a very good repeatability is described, as well as a mean to predict color fringing from optical designs.
We investigate the task of wide format still image manipulation and compression, within the framework of a document printing and copying data path. A typical document processing chain can benefit from the use of data compression, especially when it manages wide format color documents.
In order to develop a new approach to use data compression for wide format printing systems, we expose in this article the benchmarking process of compression applied to large documents. Standard algorithms, from the imaging and document processing industry have been chosen for the compression of wide format color raster images. A database of image files has been created and classified for this purpose.
The goal is to evaluate the performance in terms of data-flow reduction, along with quality losses in case of lossy compression. For the sake of a precise evaluation of performance of these compression algorithms, we include time measurements of the sole compression and decompression processes. A comparison of the memory footprint of each compression and decompression algorithms helps also to appreciate their resource consumptions.
Digital image processing algorithms are usually designed for the raw
format, that is on an uncompressed representation of the image.
Therefore prior to transforming or processing a compressed format,
decompression is applied; then, the result of the processing
application is finally re-compressed for further transfer or storage.
The change of data representation is resource-consuming in terms of
computation, time and memory usage. In the wide format printing
industry, this problem becomes an important issue: e.g. a 1 m2 input color image, scanned at 600 dpi exceeds 1.6 GB in its raw representation. However, some image processing algorithms can be performed in the compressed-domain, by applying an equivalent
operation on the compressed format.
This paper is presenting an innovative application of the halftoning processing operation by screening, to be applied on JPEG-compressed image. This compressed-domain transform is performed by computing the threshold operation of the screening algorithm in the DCT domain. This algorithm is illustrated by examples for different halftone masks. A pre-sharpening operation, applied on a JPEG-compressed low quality image is also described; it allows to de-noise and to enhance the contours of this image.
Digital image processing algorithms are usually designed for the raw format, that is on an uncompressed representation of the image. Therefore prior to transforming or processing a compressed format, decompression is applied; then, the result of the processing application is finally re-compressed for further transfer or storage. The change of data representation is resource-consuming in terms of computation, time and memory usage. In the wide format printing industry, this problem becomes an important issue: e.g. a 1 m2 input color image, scanned at 600 dpi exceeds 1.6 GB in its raw representation. However, some image processing algorithms can be performed in the compressed-domain, by applying an equivalent operation on the compressed format. We investigate the application of compression to the Wide Format Document management chain and more specifically to the image processing components. We survey the typical printing processing operations, such as rotation by multiple 90°, symmetry along vertical or horizontal axis or scaling in the JPEG compressed-domain.
We investigate the task of wide format still image manipulation and compression, within the framework of a wide format document data path. For such systems, the constraints are put on performance and cost: the use of data compression aims at reducing both storage cost and the transfer times, which are critical for wide format printing systems. Nevertheless, different factors reduce the overall system performance and usability; using inadequate compression algorithms for an inadequate document content -- that can mix text, graphics and photographs --minimizes its global usefulness. Other factors limit its usability, as the non-compatibility of compressed data-stream with basic image transformations or the pixel encoding route mostly in a raster order, that do not allow random image access. In our article, we survey the adequation of some of the existing standards and compressed file formats, with respect to the constraints of the large format document systems
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