Image processing apparatus
First Claim
1. Image processing apparatus for filtering a digital representation of a raster scanned image into a plurality of sub-bands in the two-dimensional spatial frequency domain, said raster scanned image having a resolution in a first direction and a resolution in a second direction, said raster scanned image corresponding to a reconstructed image having a resolution in the first direction and a resolution in the second direction and having aliasing distortion and ringing distortion, the aliasing distortion in said second direction being greater than in said first direction, said resolution of said raster scanned image in said first direction being greater than said resolution of said raster scanned image in said second direction such that a portion of the ringing distortion in said first direction is confined to a smaller region of said reconstructed image than a portion of the ringing distortion of equal magnitude in said second direction of said reconstructed image, said image processing apparatus comprising:
- decimation filter means having a first forward filter group comprising a first plurality of multi-tap digital decimation filters, each having a filter length, for filtering in said first direction and a second forward filter group comprising a second plurality of multi-tap digital decimation filters, each having a filter length, for filtering in said second direction, said filter lengths of said first plurality of multi-tap digital decimation filters having a mean which is greater than the mean of said filter lengths of said second plurality of multi-tap digital decimation filters such that the aliasing distortion is reduced in said first direction and the ringing distortion is reduced in said second direction without significantly increasing the aliasing distortion in said second direction.
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Abstract
Image processing apparatus is described for filtering a digital representation of a raster scanned image into a plurality of sub-bands in the two-dimensional spatial frequency domain, the resolution of the raster scanned image in a first direction (usually the horizontal direction) being greater than the resolution of the raster scanned image in a second direction (usually the vertical direction). The image processing apparatus has a decimation filter means comprising a number of multi-tap digital decimation filters for spatial filtering in the first and second directions. The mean of the filter lengths of the filters used for filtering in the first direction is greater than that of the filters used for filtering in the second direction. Complementary interpolation apparatus for reconstructing the image from the plurality of sub-bands is also described.
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Citations
27 Claims
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1. Image processing apparatus for filtering a digital representation of a raster scanned image into a plurality of sub-bands in the two-dimensional spatial frequency domain, said raster scanned image having a resolution in a first direction and a resolution in a second direction, said raster scanned image corresponding to a reconstructed image having a resolution in the first direction and a resolution in the second direction and having aliasing distortion and ringing distortion, the aliasing distortion in said second direction being greater than in said first direction, said resolution of said raster scanned image in said first direction being greater than said resolution of said raster scanned image in said second direction such that a portion of the ringing distortion in said first direction is confined to a smaller region of said reconstructed image than a portion of the ringing distortion of equal magnitude in said second direction of said reconstructed image, said image processing apparatus comprising:
decimation filter means having a first forward filter group comprising a first plurality of multi-tap digital decimation filters, each having a filter length, for filtering in said first direction and a second forward filter group comprising a second plurality of multi-tap digital decimation filters, each having a filter length, for filtering in said second direction, said filter lengths of said first plurality of multi-tap digital decimation filters having a mean which is greater than the mean of said filter lengths of said second plurality of multi-tap digital decimation filters such that the aliasing distortion is reduced in said first direction and the ringing distortion is reduced in said second direction without significantly increasing the aliasing distortion in said second direction. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 23, 24, 25)
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12. Image processing apparatus in which a reconstructed digital representation of a raster scanned image is interpolated from a plurality of sub-bands in the two-dimensional spatial frequency domain and having aliasing distortion and ringing distortion, the aliasing distortion in said second direction being greater than in said first direction, said raster scanned image having a resolution in a first direction and a resolution in a second direction, said resolution of said raster scanned image in said first direction being greater than said resolution of said raster scanned image in said second direction such that a portion of the ringing distortion in said first direction is confined to a smaller region of said reconstructed image than a portion of the ringing distortion of equal magnitude in said second direction of said reconstructed image, said image processing apparatus comprising:
interpolation filter means having a first filter group comprising a first plurality of multi-tap digital interpolation filters, each having a filter length, for filtering in said first direction and a second filter group comprising a second plurality of multi-tap digital interpolation filters, each having a filter length, for filtering in said second direction, said filter lengths of said first plurality of multi-tap digital interpolation filters having a mean which is greater than the mean of said filter lengths of said second plurality of multi-tap digital interpolation filters such that the aliasing distortion is reduced in said first direction and the ringing distortion is reduced in said second direction without significantly increasing the aliasing distortion in said second direction. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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26. A method of filtering a digital representation of a raster scanned image into a plurality of sub-bands in the two-dimensional spatial frequency domain, said raster scanned image having a resolution in a first direction and a resolution in a second direction, said raster scanned image corresponding to a reconstructed image having a resolution in the first direction and a resolution in the second direction and having aliasing distortion and ringing distortion, the aliasing distortion in said second direction being greater than in said first direction, said resolution of said raster scanned image in said first direction being greater than said resolution of said raster scanned image in said second direction such that a portion of the ringing distortion in said first direction is confined to a smaller region of said reconstructed image than a portion of the ringing distortion of equal magnitude in said second direction of said reconstructed image, said method comprising the steps of:
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(I) filtering in said first direction with a first plurality of multi-tap digital decimation filters, each having a filter length; and (II) filtering in said second direction with a second plurality of multi-tap digital decimation filters, each having a filter length, said filter lengths of said first plurality of multi-tap digital decimation filters having a mean which is greater than the mean of the filter lengths of said second plurality of multi-tap digital decimation filters such that the aliasing distortion is reduced in said first direction and the ringing distortion is reduced in said second direction without significantly increasing the aliasing distortion in said second direction.
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27. A method of interpolating a reconstructed digital representation of a raster scanned image from a plurality of sub-bands in the two-dimensional spatial frequency domain and having aliasing distortion and ringing distortion, the aliasing distortion in said second direction being greater than in said first direction, said raster scanned image having a resolution in a first direction and a resolution in a second direction, said resolution of said raster scanned image in said first direction being greater than said resolution of the raster scanned image in said second direction such that a portion of the ringing distortion in said first direction is confined to a smaller region of said reconstructed image than a portion of the ringing distortion of equal magnitude in said second direction of said reconstructed image, said method comprising the steps of:
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(I) filtering in said first direction with a first plurality of multi-tap digital interpolation filters, each having a filter length; and (II) filtering in said second direction with a second plurality of multi-tap digital interpolation filters, each having a filter length, said filter lengths of said first plurality of multi-tap digital interpolation filter having a mean which is greater than the mean of said filter lengths of said second plurality of multi-tap digital interpolation filters such that the aliasing distortion is reduced in said first direction and the ringing distortion is reduced in said second direction without significantly increasing the aliasing distortion in said second direction.
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Specification