Showing papers on "Dark-frame subtraction published in 1989"
10 Jul 1989
TL;DR: A noise model is defined for remotely sensed images, and the noise statistics are estimated by using the means and variances from small image blocks to detect a straight line through the maj or cluster of data points.
Abstract: A noise model is defined for remotely sensed images, and the noise statistics are estimated by using the means and variances from small (4x4 or 8x8) image blocks. Since most images contain many small but homogeneous areas, a scatter plot of variance vs (mean)' reveals characteristics of the noise. The Hough transform is then applied to the scatter plot to detect a straight line through the maj or cluster of data points. This defines the image noise statistics. Images from SAR, Landsat TM, and passive microwave Sensors are used for illustration.
132 citations
TL;DR: In this paper, the authors studied the distribution of noise in optical images produced by the aperture synthesis technique, in which the principal source of noise is the intrinsic shot noise of photoelectric detection.
Abstract: We study the distribution of noise in optical images produced by the aperture synthesis technique, in which the principal source of noise is the intrinsic shot noise of photoelectric detection. The results of our analysis are directly applicable to any space-based optical interferometer. We show that the signal-to-noise ratio of images synthesized by such an ideal interferometric array is essentially independent of the details of the beam-combination geometry, the degree of array redundancy, and whether zero-spatial-frequency components are included in image synthesis. However, the distribution of noise does depend on the beam-combination geometry. A highly desirable distribution, one of uniform noise across the entire image, is obtained only when the beams from the n primary apertures are subdivided and combined pairwise on n(n - 1)/2 detectors.
29 citations
TL;DR: In this article, the noise perception limit and the dependence of random noise and fixed pattern noise (FPN) on signal charge in a CCD imager were measured to obtain a correlation between measured noise and subjective noise.
Abstract: To achieve a high-performance image sensor for a broadcast TV camera, several studies of the noise characteristics of a CCD image sensor are described. The noise perception limit and the dependence of random noise and fixed pattern noise (FPN) on signal charge in a CCD imager were measured to obtain a correlation between measured noise and subjective noise. A method has been devised to measure FPN and random noise separately. Using this method, it has been confirmed that noise can be reduced to less than the perception limit using new noise-suppression techniques. >
24 citations
01 Jan 1989
TL;DR: In this paper, a new filtering method was proposed for Positron Emission Tomography (PET) images that works as follows: the image is converted from the rectangular z-y coordinate system to the polar p-8 coordinate system.
Abstract: The quality of Positron Emission Tomography (PET) images is often degraded by radial noise. Because this noise cannot be easily isolated either in the spatial or frequency domain, classical spatial and frequency techniques failed in removing this noise. As an alternative, we ptwpose a new filtering method that works as follows. The image is converted from the rectangular z-y coordinate system to the polar p-8 coordinate system. This causes the mdial noise to map into horizontal lines. Using the Fourier transform, mdial noise is then mapped into and around the vertical azis of the Fourier spectrum in the corresponding w+ space. A class of filters is designed and applied to these images. The filtered images are then converted back to rectangular coordinates system for display and examination. This method has been tested using both synthetic and real data. The corrected images show minor residual noise and practically no loss of information around the heart wall.
1 citations
06 Sep 1989
TL;DR: In this paper, the photon noise contribution has been derived, taking into account that some pixels are brighter than others when the camera is exposed to uniform illumination, and when the object being imaged is very dim, or exposure time for a single frame is very short, the computed bispectrum with exhibit a photon noise component due to the Poisson statistical nature of the photon detection process.
Abstract: Summary form only given. Recent work in developing techniques for the removal of photon noise (shot noise) from two-dimensional power spectra and bispectra is reported. The general problem of speckle imaging (i.e. imaging through atmospheric turbulence), has been addressed. The general approach is to take a set of very-short-exposure frames (1-10 ms), compute some quantity like the power spectrum or bispectrum for each frame, and average this quantity over all the frames. These averaged quantities can be used to reconstruct the image. However, when the object being imaged is very dim, or the exposure time for a single frame is very short, the computed bispectrum with exhibit a photon noise component due to the Poisson statistical nature of the photon detection process. The photon noise contribution has been derived, taking into account that some pixels are brighter than others when the camera is exposed to uniform illumination. >