EP0287891A2 — Apparatus and method of attenuating distortion in…

Claim 1

Independent Claim 188 words

In a graylevel image data processing system (100) which includes (A) a predictive coder which (i) computes a predictive difference value D for the current pixel and (ii) quantizes (102) the difference D to a QN value wherein the number of QN values is less than the number of permitted D values, wherein QN=Q0 corresponds to a region of substantially uniform graylevel, with associated small D values, and wherein ranges of larger D values correspond to QN values of relatively larger magnitudes and (B) an entropy encoder (120) which receives as input and compresses QN value data from the predictive coder, a machine-implemented method for reducing distortion in an image reconstructed from data subjected to compression by predictive coding, the method being characterized by the steps of: (a) for each pixel at which QN=Q0, setting (106) a value QERR equal (b) remapping (108) the set QERR value to a value MERR; (c) summing (110) the MERR values for successive pixels in a QN=Q0 region; and (d) for a pixel at which the sum of MERR values reaches (112, 114) a predefined threshold, adjusting (104) the QN value thereof.

Claim 2

Dependent Claim 188 words

In a graylevel image data processing system (100) which includes (A) a predictive coder which (i) computes a predictive difference value D for the current pixel and (ii) quantizes (102) the difference D to a QN value wherein the number of QN values is less than the number of permitted D values, wherein QN=Q0 corresponds to a region of substantially uniform graylevel, with associated small D values, and wherein ranges of larger D values correspond to QN values of relatively larger magnitudes and (B) an entropy encoder (120) which receives as input and compresses QN value data from the predictive coder, a machine-implemented method for reducing distortion in an image reconstructed from data subjected to compression by predictive coding, the method being characterized by the steps of: (a) for each pixel at which QN=Q0, setting (106) a value QERR equal (b) remapping (108) the set QERR value to a value MERR; (c) summing (110) the MERR values for successive pixels in a QN=Q0 region; and (d) for a pixel at which the sum of MERR values reaches (112, 114) a predefined threshold, adjusting (104) the QN value thereof.

Claim 3

Dependent Claim 36 words

The method of claim 1 wherein step (b) also includes: (e) assigning to the value MERR=0 those QERR values in which |QERR| ≦ (+Q1 VALUE)/2 where Q1 is the quantization level closest in value to Q0.

Claim 4

Dependent Claim 51 words

The method of claim 1 or 2 wherein step (b) includes the steps of: (f) re-mapping QERR=-4 and QERR=-3 to an MERR value of -1; (g) re-mapping QERR=-2, QERR=-1, QERR=0, QERR=1 and QERR=2 to an MERR value of 0; and (h) re-mapping QERR=3 and QERR=4 to an MERR value of 1.

Claim 5

Independent Claim 41 words

The method of any preceding claim wherein step (d) includes the steps of: (j) adjusting the QN value from the Q0 value by the Q1 value when the sum reaches a predefined threshold; and (k) resetting the sum of MERR values.

Claim 6

Independent Claim 85 words

The method of any preceding claim comprising the further steps of: (l) reconstructing (126, 130) graylevel values for pixels in the image; and (m) filtering (132) the reconstructed value I₀ for a current pixel to provide a filtered value of Iʹ₀ which is equal to I₀ + [(I₋₁- I₀) C- + (I₊₁ - I₀) C+ ] wherein C+ and C- are respective predefined clamping values, and wherein I₋₁ and I₊₁ are the respective reconstructed values of pixels adjacently below and adjacently above the current pixel.

Claim 7

Dependent Claim 29 words

The method of claim 5 comprising the further step of: (n) repeating step (m) with one pixel after another in one alternating row after another being the current pixel.

Claim 8

Dependent Claim 205 words

A predictive coding system comprising an encoder (100) which supplies the output thereof to an entropy encoder (120), the predictive coding encoder (100) comprising: means for computing a value D representing the difference between an original graylevel value for a current pixel and a predicted value for the current pixel; quantizer means (102) for electronically associating each successive range of possible D values to a respective quantization level, each quantization level QN having a respective QN value representing the range corresponding thereto; and characterized by: switching means (106) for setting a value QERR to D when QN=Q0 wherein Q0 represents the lowest quantization level; means (108) for receiving QERR output from the switching means and re-mapping QERR values to MERR values so that the value MERR=0 is assigned to those QERR values in which |QERR| ≦ (+Q1 VALUE)/2 wherein Q1 VALUE is the value corresponding to the quantization level QN=Q1; means (110) for summing the MERR values for successive pixels in a QN=Q0 region; and means (112, 114, 104) for receiving as input the MERR value sum and for adjusting the QN value from the value of Q0 by the magnitude of Q1 for a pixel at which the summed value reaches a predefined threshold.

Claim 9

Dependent Claim 205 words

A predictive coding system comprising an encoder (100) which supplies the output thereof to an entropy encoder (120), the predictive coding encoder (100) comprising: means for computing a value D representing the difference between an original graylevel value for a current pixel and a predicted value for the current pixel; quantizer means (102) for electronically associating each successive range of possible D values to a respective quantization level, each quantization level QN having a respective QN value representing the range corresponding thereto; and characterized by: switching means (106) for setting a value QERR to D when QN=Q0 wherein Q0 represents the lowest quantization level; means (108) for receiving QERR output from the switching means and re-mapping QERR values to MERR values so that the value MERR=0 is assigned to those QERR values in which |QERR| ≦ (+Q1 VALUE)/2 wherein Q1 VALUE is the value corresponding to the quantization level QN=Q1; means (110) for summing the MERR values for successive pixels in a QN=Q0 region; and means (112, 114, 104) for receiving as input the MERR value sum and for adjusting the QN value from the value of Q0 by the magnitude of Q1 for a pixel at which the summed value reaches a predefined threshold.

Claim 10

Dependent Claim 118 words

A predictive coding system as set forth in claim 7 further comprising a vertical filter (132) for adjusting the reconstructed (130) value I₀ of a current pixel in an image where the pixel adjacently above the current pixel has a value I₊₁ and the pixel adjacently below has a value I₋₁, the filter being characterized by: means for computing a first difference (I₋₁ - I₀); means for computing a second difference (I₊₁ - I₀); means for clamping the first difference and second difference to prescribed limits C- and C+, respectively; and means for computing a filtered value Iʹ₀ for the current pixel to be equal to I₀ + [(I₋₁ - I₀) C- + (I₊₁ - I₀) C+ ].

Claim 11

Dependent Claim 76 words

The system comprising a vertical filter as in claim 8 wherein said Iʹ₀ computing means includes: means for interpolating the value of I₋₁ as where I₋₂ is the value of a pixel two pixels down from the current pixel; means for interpolating the value of I₊₁ as where I₊₂ is the value of a pixel two pixels up from the current pixel; and means for computing Iʹ₀ based on the interpolated values of I₋₁ and I₊₁.

Apparatus and method of attenuating distortion introduced by a predictive coding image compressor

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