scispace - formally typeset
Search or ask a question

Showing papers on "Dark-frame subtraction published in 1987"


Patent
30 Nov 1987
TL;DR: In this paper, it is proposed to deform one of the images locally so that the motion of the parts which should remain stationary is compensated for, by subtracting the locally deformed image from the other image, a subtraction image will be obtained which is substantially free from motion artefacts and which contains only the information of the moving contrast medium.
Abstract: Subtraction images formed by digital subtraction angiography contain artefacts due to the motions of the patient. This motion disturbs the condition imposed for subtraction imaging that only the introduced contrast medium is displaced and that the remainder must remain stationary. For example, when ribs of the patient have moved, due to respiration, between the formation of the first image and the second image, this motion will appear as undesirable information (the extent of the motion of the ribs) in the subtraction image. It is proposed to deform one of the images locally so that the motion of the parts which should remain stationary is compensated for. By subtracting the locally deformed image from the other image, a subtraction image will be obtained which is substantially free from motion artefacts and which contains only the information of the moving contrast medium. To achieve this, a shift vector is determined for various pixels and a reliability criterion is calculated for each direction component of said shift vector.

45 citations


Proceedings Article
01 Jan 1987
TL;DR: In this paper, an adaptive algorithm based on the calculation of the local statistics around a pixel is applied to 1-look SAR imagery, which adapts to the nonstationarity of the image statistics since the size of the blocks is very small compared to the image.
Abstract: Speckle noise is inherent to synthetic aperture radar (SAR) imagery. Since the degradation of the image due to this noise results in uncertainties in the interpretation of the scene and in a loss of apparent resolution, it is desirable to filter the image to reduce this noise. In this paper, an adaptive algorithm based on the calculation of the local statistics around a pixel is applied to 1-look SAR imagery. The filter adapts to the nonstationarity of the image statistics since the size of the blocks is very small compared to that of the image. The performance of the filter is measured in terms of the equivalent number of looks (ENL) of the filtered image and the resulting resolution degradation. The results are compared to those obtained from different techniques applied to similar data. The local adaptive filter (LAF) significantly increases the ENL of the final image. The associated loss of resolution is also lower than that for other commonly used speckle reduction techniques.

17 citations


Proceedings ArticleDOI
01 Jan 1987

11 citations


Patent
12 Feb 1987
TL;DR: In this article, a method for the non-medical X-ray image processing for determining the spatial distribution of the noise and of the sensitivity in an Xray image is proposed. But the method is not suitable for the analysis of medical images.
Abstract: The invention relates to a method for the non-medical X-ray image processing for determining the spatial distribution of the noise and of the sensitivity in an X-ray image. The noise or sensitivity image, respectively, can be generated by pixel-by-pixel subtraction of two X-ray pictures whilst a noise image can also be generated by forming the square root in each individual pixel of an X-ray picture.

3 citations