Showing papers on "Histogram equalization published in 1985"

Histogram equalization of CT images.

Abstract: Histogram equalization for display of clinical CT images was evaluated. In theory, histogram equalization makes optimal use of an available grey scale to display an image, and its use could circumvent the problem of selecting specific window settings for each image. In several clinical images, the use of a spatially variable histogram equalization technique limited to that portion of the CT image occupied by the patient did appear to increase the visibility of anatomic structures. However, using the technique also increased displayed image noise and artifacts. Although radiologists found this to be objectionable, it did not decrease the detectability of simulated low-contrast liver metastases. Further evaluation of histogram equalization for displaying CT images is being pursued.

Digital color image processing method and apparatus employing three color reproduction functions for adjusting both tone scale and color balance

Abstract: A digital color image processing method and apparatus is characterized by producing three color reproduction functions by normalizing samples of color values from three color components of a digital image. The color reproduction functions are applied to the respective color components of the image to produce dimensionless Z values. A contrast adjusting constant is computed and the dimensionless Z values are multiplied by the constant to adjust the contrast of the processed image. Finally a constant representing the mean density for each of the color components for a particular output medium is added to the contrast adjusted Z values to produce the processed digital image.

Recognition of bones from X-rays of the hand†

Abstract: Algorithms for the computer recognition of bones in an X-ray of the hand and wrist are described by analysing age-related changes that take place with growth in the bones. Since a straightforward structural description is inadequate because of these changes, the paper considers a shape description technique based on linear measurements (axial length, width and location) from a polygonal approximation of the bones. The recognition algorithm also needs strong a priori knowledge of the structure of the hand. System effectiveness is demonstrated on some sections of two typical X-rays of 10–12-year-old boys when histogram equalization, thresholding and edge detection, and octal code generation techniques are included in the preprocessing algorithm.

Entropy-Constant Image Enhancement by Histogram Transformation

Abstract: Image enhancement techniques are described for increasing visual contrast in an intensity range (or ranges) of interest. Enhancement is accomplished by histogram transformation where (except for quantization error) there is no change in entropy between the input and output images. This preservation of entropy is desired for some applications where it is imperative that no artifacts be introduced - as may result from such enhancement techniques as spatial filtering and adaptive histogram transformation. The contribution of this work is toward the compilation and organization of useful image enhancement techniques and toward an understanding of matching particular transformations with the desired purposes. Two types of methods for obtaining histogram transformations are distinguished here. In one type the output histogram is specified as a ramp-shaped function, and the transformation is found. This type is useful for automatically enhancing low or high intensity ranges, and for histogram equalization. For the second type, the general form of the transformation function is defined to be a third order polynomial function, which is specified by the choice of the intensity region of interest and the desired amount of contrast enhancement. This type is useful for interactive enhancement. Examples are shown which illustrate where each of the transformations is applicable, and what results are obtained from such transformations.

Port Film Enhancement By Digital Processing

Abstract: Port films are routinely exposed during radiotherapy treatment to verify correct patient positioning. Contrast is always poor, due to the high energy of the radiation, and spatial resolution is seriously degraded by scatter and large penumbra. We place port films on an illuminated panel facing a vidicon camera, and obtain digitized images for processing in our DICOM-8 digital imaging computer. Averaging up to 256 frames reduces camera noise. Convolution filtering, windowing, histogram equalization and blurred mask subtraction lead to significant improvement in the perception of anatomical structures. Digitization of the x-ray simulator film, using real-time subtraction for accurate alignment, permits the direct comparison of the actual field size with the prescribed treatment area.

Picture Enhancement and Preparation

Abstract: Pictures carry information for visual perception. To help the user to appreciate this information, it is frequently necessary to prepare the picture in some way. This chapter describes the methods by which this is achieved.