Imagesetter output resolution in newspaper color image reproduction

The use of color in newspaper printing has significantly increased over the last few years. To compete with other news media, advertising as well as editorial design had to become more visually attractive, using more color graphics and images. The concurrent development of integrated desktop pre-press systems facilitated the integration of color, having less cost associated with new technology purchases than the traditional high end systems. The purpose of the thesis is to compare different output resolutions of an imagesetter and to find the minimal output resolution necessary for acceptable quality in newspaper color image reproduction. The speed of an imagesetter, which is dependant on the chosen output resolution, is an important factor in newspaper turn-around time. In this study, a matrix was designed containing various test targets and four different images with different image characteristics at four different output resolutions. Most imagesetters on the market today support output resolutions that approximate the four selected for the study (846, 1016, 1270, and 1693 spots per inch). The screen frequency of the images was 85 lines per inch, a common screen ruling in newspaper reproduction. The separations were output on a Linotronic 530 imagesetter. The output time varied from 18 minutes at the lowest resolution of 846 SPI to about half an hour at the highest resolution of 1693 spi. The test matrix was printed on Consolidated Newsprint on an offset newspaper Goss Community press. The print application\u27s spatial resolving power was evaluated by exarnining Fresnel zone plate resolution targets under magnification. Due to ink spreading, no visible difference could be detected on the printed test matrix between the different output resolutions. The test matrix was also submitted to an audience for visual evaluation. The psychometric method applied was the paired comparison method, which is based on the principle that the percentage of observers preferring a stimulus over the other gives a direct indication of how the two stimuli differ. In this study, the stimuli were the images with different output resolutions. Each reproduction was paired with another image from the same type, but with another output resolution. The observers had to indicate if they preferred the left or right image of a pair. The criterion for evaluation was better. The statistical analysis of the paired comparison method indicates that for all four images combined, there is a 95 percent confidence level that no visual difference in quality between the four resolutions could be detected by the observers. Experimental noise, specifically registration, skewed some of the individual image results. As a result, the first hypothesis-the visual quality of images reproduced in newspapers is not dependent on the imagesetter output resolution above a certain limit for a given set of print parameters-was proven to be correct. However, the second hypothesis-for offset newspaper printing on consolidated newsprint at a screen frequency of 85 lpi, the resolution limit lies between 1,000 and 1,200 SPi-has to be rejected. This study concludes that for the given print parameters, the resolution limit is 846 spi. Further studies might even indicate a lower limit. To summarize, one of the major disadvantages of electronic halftone reproductions today, namely output speed, can be optimized independently from technical considerations such as hardware and software systems. A ininimal output resolution can be found for a given print application by exarnining its characteristics, such as resolving power and print contrast. Any image output at a resolution higher than the mirtirnum does not improve the quality of the reproduction, and only slows down the production turn-around time

Drone Shadow Tracking

Aerial videos taken by a drone not too far above the surface may contain the drone's shadow projected on the scene. This deteriorates the aesthetic quality of videos. With the presence of other shadows, shadow removal cannot be directly applied, and the shadow of the drone must be tracked. Tracking a drone's shadow in a video is, however, challenging. The varying size, shape, change of orientation and drone altitude pose difficulties. The shadow can also easily disappear over dark areas. However, a shadow has specific properties that can be leveraged, besides its geometric shape. In this paper, we incorporate knowledge of the shadow's physical properties, in the form of shadow detection masks, into a correlation-based tracking algorithm. We capture a test set of aerial videos taken with different settings and compare our results to those of a state-of-the-art tracking algorithm.Comment: 5 pages, 4 figure

Evaluation of a Hyperspectral Image Database for Demosaicking Purposes

International audienceWe present a study on the the applicability of hyperspectral images to evaluate color filter array (CFA) design and the performance of demosaicking algorithms. The aim is to simulate a typical digital still camera processing pipe-line and to compare two different scenarios: evaluate the performance of demosaicking algorithms applied to raw camera RGB values before color rendering to sRGB, and evaluate the performance of demosaicking algorithms applied on the final sRGB color rendered image. The second scenario is the most frequently used one in literature because CFA design and algorithms are usually tested on a set of existing images that are already rendered, such as the Kodak Photo CD set containing the well-known lighthouse image. We simulate the camera processing pipe-line with measured spectral sensitivity functions of a real camera. Modeling a Bayer CFA, we select three linear demosaicking techniques in order to perform the tests. The evaluation is done using CMSE, CPSNR, s-CIELAB and MSSIM metrics to compare demosaicking results. We find that the performance, and especially the difference between demosaicking algorithms, is indeed significant depending if the mosaicking/demosaicking is applied to camera raw values as opposed to already rendered sRGB images. We argue that evaluating the former gives a better indication how a CFA/demosaicking combination will work in practice, and that it is in the interest of the community to create a hyperspectral image dataset dedicated to that effect

Color Encodings for Image Databases

There are a number of color encoding standards that have lately been developed ant are being proposed to the imaging community for different encoding steps in the color imaging workflow, optimized for different purposes. In this paper, their applicability for master and derivative image file encoding for image databases is discussed. Several types of image databases are defined, and the advantages and disadvantages of archiving master files after different image workflow steps are outlined. Several input- and output-referred encodings are summarized and discussed in relation to their applicability for image database file encoding

Color Strategies for Image Databases

In this paper, color encoding strategies for different image database applications are discussed. The color image workflow is examined in detail, and master and derivative file encoding strategies are outlined in relation to capture, maintenance, and deployment of image files. For the most common image database purposes, recommendations are given as to which type of color encoding is most suitable. Advantages and disadvantages of sensor, input-referred, output-referred, and output device specific color encodings are discussed in relation with image usage. The role of ICC color management in an image database environment is also considered