Image signal processing with digital filtering to minimize aliasing caused by image manipulation
First Claim
1. An image processing apparatus for manipulating an input image by rotating and/or compressing said input image, said apparatus comprising:
- receiving means for receiving a digital input signal having a plurality of words representing said input image in which each of said words has a respective position with horizontal and vertical coordinates; and
manipulating means for manipulating said input image so as to form a manipulated image, said manipulating means including address generating means for generating respective addresses for successive words of said digital input signal;
local scaling factor computation means computing respective horizontal and vertical local scaling factors representing amounts of compression and rotation in horizontal and vertical directions, respectively, for successive local areas of said manipulated image based on sets of said addresses generated for sets of said words of said input image in which each of said sets of said words includes first and second words that are horizontally spaced in said input image and a third word that is aligned vertically with said second word in said input image, each of said horizontal local scaling factors corresponding to the length of a line that extends perpendicularly from a line passing through the respective positions of said second and third words to the position of said first word in each of said successive local areas in said manipulated image and each of said vertical local scaling factors corresponding to the length of a line that extends perpendicularly from a line passing through the respective positions of said first and second words to the position of said third word in each of said successive local areas in said manipulated image;
bandwidth control means responsive to the successive horizontal and vertical local scaling factors for generating horizontal and vertical bandwidth control signals; and
a digital filter having variable horizontal and vertical bandwidths for respectively varying said horizontal and vertical bandwidths in response to said horizontal and vertical bandwidth control signals and for performing two-dimensional filtering of said digital input signal so as to minimize the amount of aliasing errors that would be caused by the manipulation of said local areas.
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Abstract
An image signal processing apparatus has an address generator that generates addresses for successive words of a digital input signal representing an input image to be manipulated. A computation circuit monitors the addresses for successive word sets which each comprise first and second words relatively horizontally spaced in the input image and a third word aligned vertically with the second word, and computes from each set both horizontal and vertical local scaling factors representing the extent of compression in the horizontal and vertical directions of a corresponding local area of the manipulated image. A bandwidth controller is responsive to the successive scaling factors to vary the horizontal and vertical bandwidths of a digital filter which two-dimensionally filters the input image, thereby to minimize aliasing that would be caused by the manipulation of the local areas. The computation circuit computes the scaling factors for each local area such that the horizontal factor corresponds to the length of a line that extends perpendicularly from a line passing through the positions of the second and third words in the manipulated image to the position of the first word and the vertical factor corresponds to the length of a line that extends perpendicularly from a line passing through the positions of the first and second words to the position of the third word.
120 Citations
14 Claims
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1. An image processing apparatus for manipulating an input image by rotating and/or compressing said input image, said apparatus comprising:
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receiving means for receiving a digital input signal having a plurality of words representing said input image in which each of said words has a respective position with horizontal and vertical coordinates; and manipulating means for manipulating said input image so as to form a manipulated image, said manipulating means including address generating means for generating respective addresses for successive words of said digital input signal;
local scaling factor computation means computing respective horizontal and vertical local scaling factors representing amounts of compression and rotation in horizontal and vertical directions, respectively, for successive local areas of said manipulated image based on sets of said addresses generated for sets of said words of said input image in which each of said sets of said words includes first and second words that are horizontally spaced in said input image and a third word that is aligned vertically with said second word in said input image, each of said horizontal local scaling factors corresponding to the length of a line that extends perpendicularly from a line passing through the respective positions of said second and third words to the position of said first word in each of said successive local areas in said manipulated image and each of said vertical local scaling factors corresponding to the length of a line that extends perpendicularly from a line passing through the respective positions of said first and second words to the position of said third word in each of said successive local areas in said manipulated image;
bandwidth control means responsive to the successive horizontal and vertical local scaling factors for generating horizontal and vertical bandwidth control signals; and
a digital filter having variable horizontal and vertical bandwidths for respectively varying said horizontal and vertical bandwidths in response to said horizontal and vertical bandwidth control signals and for performing two-dimensional filtering of said digital input signal so as to minimize the amount of aliasing errors that would be caused by the manipulation of said local areas. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for manipulating an input image by rotating and/or compressing said input image, said method comprising the steps of:
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receiving a digital input signal having a plurality of words representing said input image in which each of said words has a respective position with horizontal and vertical coordinates; and manipulating said input image so as to form a manipulated image, the step of manipulating including generating respective addresses for successive words of said digital input signal;
computing respective horizontal and vertical local scaling factors representing amounts of compression and rotation in horizontal and vertical directions, respectively, for successive local areas of said manipulated image based on sets of said addresses generated for sets of said words of said input image in which each of said sets of said words includes first and second words that are horizontally spaced in said input image and a third word that is aligned vertically with said second word in said input image, each of said horizontal local scaling factors corresponding to the length of a line that extends perpendicularly from a line passing through the respective positions of said second and third words to the position of said first word in each of said successive local areas in said manipulated image and each of said vertical local scaling factors corresponding to the length of a line that extends perpendicularly from a line passing through the respective positions of said first and second words to the position of said third word in each of said successive local areas in said manipulated image;
generating horizontal and vertical bandwidth control signals in response to the successive horizontal and vertical local scaling factors;
varying horizontal and vertical bandwidths of a digital filter in response to said horizontal and vertical bandwidth control signals; and
performing two-dimensional filtering of said digital input signal by said digital filter so as to minimize the amount of aliasing errors that would be caused by the manipulation of said local areas. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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Specification