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1. (WO1993017394) PROCEDE ET APPAREIL POUR REALISER D'UNE MANIERE ADAPTATIVE L'INTERPOLATION D'UNE IMAGE NUMERIQUE
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WHAT IS CLAIMED IS:

1. A method of processing a digital input image into an interpolated digital output image, comprising the steps of:

(a) obtaining input pixel data of said input image;

(b) locating a local position within said input
image for interpolation;

(c) obtaining a first interpolated output image
pixel at a predetermined pixel position in said output image;

(d) obtaining a second interpolated output image
pixel at said predetermined pixel position in
said output image;

(e) deriving an input image characteristic value
from said input image pixel data; and

(f) calculating a resultant output image pixel at
said predetermined pixel position in said output image by combining said first and said second
interpolated output image pixels as a function
of said input image characteristic value.

2. The method according to claim 1, wherein said input image characteristic value is derived from a portion of said input pixel data which is representative of said local position.

3. A method according to claim 1, wherein said first interpolated output image pixel is obtained by the application of a first interpolation algorithm producing a relatively sharp result and said second interpolated output image pixel is obtained by the application of a second interpolation algorithm
producing a relatively soft result.

4. The method according to claim 3, wherein said sharp and said soft interpolated output image pixels are obtained by the application of precalculated
weighting coefficients obtained from said first and second interpolation algorithms, respectively.

5. The method according to claim 1, further comprising the steps of:

obtaining a third interpolated output image pixel at said predetermined pixel position in said output
image;

deriving a further input image characteristic value from said input image pixel data; and

calculating a further resultant output image pixel at said predetermined pixel position in said output
image by combining said first resultant output image pixel and said third interpolated output image pixel as a function of said further input image
characteristic value.

6. The method according to claim 5, wherein said
resultant output image pixel is calculated according to the algorithm:

P = SX + (1 - S)Y

where P represents said resultant output image pixel;

X represents said first interpolated output image
pixel;

Y represents said second interpolated output image pixel; and

S represents a scaling factor, with a value of from 0 to 1, derived from said input image characteristic value,

and wherein

said further resultant output image pixel is
calculated by using the algorithm:

P1 = s'w + (1 - s')P

where P represents said further resultant output
image pixel; W represents said third interpolated
output image pixel and S represents a further
scaling factor with a value from 0 to 1, derived from said further input image characteristic value.

7. The method according to claim 1, wherein said first and said second interpolated output image pixels are each obtained by selection from a set of
precalculated first and second interpolated output image pixels, respectively.

8. The method according to claim 3 , wherein said
resultant output image pixel is calculated according to the algorithm:

P ****- SX + (1 - S)Y where

P represents said resultant output image pixel;

X represents said first or sharp interpolated output image pixel;

Y represents said second or soft interpolated output image pixel; and

S represents a scaling factor, with a value of from 0 to 1, derived from said input image characteristic value.

9. The method according to claim 8, wherein said input image is a colored image comprising a number of basic colors and further comprising the step of providing a multidimensional lookup table, the number of
dimensions corresponding with said number of basic colors, said lookup table mapping input image
characteristic values for each one of said basic
colors to a corresponding value for said scaling
factor.

10. The method according to claim 9, wherein said number of basic colors is three.

11. The method according to claim 9, wherein said number of basic colors is four.

12. The method according to claim 8, wherein said scaling factor S is derived from two separate input image
characteristic values.

13. The method according to claim 12 , wherein said two separate input image characteristic values comprise input image contrast and input image density at said local position in said input image.

14. The method according to claim 13, wherein said input image contrast is generated from said input image data by convolving a set of contrast weighting
coefficients with said input image data.

15. The method according to claim 14, wherein said input image density is taken to be proportional to said relatively soft interpolated output image pixel.

16. The method according to claim 14, wherein said input image density is derived from said input image data.

17. The method according to claim 12, further comprising the step of providing lookup tables mapping said
input image characteristic values to corresponding values for said scaling factor.

18. The method according to claim 17 , wherein said lookup tables comprise two one-dimensional lookup tables mapping input image contrast and density,
respectively, to corresponding intermediate values for said scaling factor and the method further
comprises the step of multiplying said intermediate values together to produce said scaling factor.

19. The method according to claim 1, wherein said input image characteristic value comprises input image
contrast.

20. The method according to claim 1, wherein said input image characteristic value comprises input image
density.

21. The method according to claim 1, further comprising, the step of deriving a second image characteristic value from said input pixel data and calculating said resultant output pixel by combining said first and second output image pixels as a function of said
first and second image characteristic values.

22. The method according to claim 21, wherein said first and second characteristic values comprise values
representing image contrast and density,
respectively.

23. The method according to claim 1, further comprising the steps of locating a second local position within said input image; repeating the steps (c) to (f) to obtain a further resultant output image pixel; and repeating said steps for further local positions
until a complete interpolated output image of a
required size is produced.

24. Digital image processing apparatus for interpolating a digital input image into an interpolated output
image, comprising:

an input buffer for accommodating pixel data of said input image;

a coefficient buffer for storing pre-calculated
interpolation weighting coefficients prior to real time image interpolation and comprising a first
memory segment for containing a set of precalculated relatively sharp interpolating weighting coefficients obtained by using a relatively sharp
interpolating algorithm; a second memory segment for containing a set of pre-calculated relatively soft weighting coefficients obtained by using a relatively soft interpolating algorithm; and a third memory
segment for containing a set of pre-calculated
weighting coefficients representative of a
predetermined characteristic of said input image; and

image convolution and interpolation means for
calculating a relatively sharp interpolated output image pixel using said input pixel data and said set of relatively sharp weighting coefficients and for calculating a relatively soft interpolated output
image pixel using said input pixel data and said set of relatively soft weighting coefficients and for
calculating a value for said image characteristic
using said input pixel data and said image
characteristic weighting coefficients and for
calculating a resultant output pixel by combining
said relatively sharp and said relatively soft output image pixels as a function of said characteristic
value.

25. The apparatus according to claim 24, wherein said
coefficient buffer further comprises a fourth memory segment for containing precalculated interpolation coefficients for effecting constant interpolation
coefficients for effecting constant image size
interpolation.

26. Digital image processing apparatus for interpolating a digital input image into an interpolated output
image, comprising: an input buffer for accommodating pixel data of said input image;

means for locating a local position within said
input image for interpolation;

means for obtaining a first interpolated output image pixel at a predetermined pixel position in said
interpolated output image;

means for obtaining a second interpolated output
image pixel at said predetermined pixel position;

means for deriving an input image characteristic
value from said input image pixel data; and

means for calculating a resultant output image pixel at said predetermined position in said output image by combining said first and second interpolated
output image pixels as a function of said input image characteristic value.

27. The apparatus according to claim 26, wherein said
first interpolated output image pixel is obtained by the application of a first interpolation algorithm producing a relatively sharp result and said second interpolated output image pixel is obtained by the application of a second interpolation algorithm
producing a relatively soft result.

28. The apparatus according to claim 27, wherein said
resultant output image pixel is calculated according to the algorithm:

P = SX + (1 - S)Y where

P represents said resultant output image pixel;

X represents said first or sharp interpolated output image pixel;

Y represents said second or soft interpolated output image pixel; and

S represents a scaling factor, with a value of from 0 to 1, derived from said input image characteristic value.

29. The apparatus according to claim 28, wherein said
means for deriving an input image characteristic is adapted to derive values for image contrast and image density.

30. The apparatus according to claim 29, further
comprising lookup tables for obtaining said scaling factor S as a function of said image contrast and
image density values.

31. The apparatus according to claim 30, further
comprising a coefficient buffer containing a set of contrast detector mask coefficients for deriving said image contrast value.

32. The apparatus according to claim 31, wherein said
coefficient buffer further contains a set of
precalculated sharp interpolating weighting
coefficients obtained by interpolating weighting
coefficients obtained by using said relatively sharp interpolation algorithm, a set of precalculated relatively soft weighting coefficients obtained by
using said soft interpolating algorithm.

33. The apparatus according to claim 26, further
5 comprising means for obtaining a third interpolated
output image pixel at said predetermined pixel
position in said output image;

means for deriving a further input image
0 characteristic value from said input image pixel
data; and

means for calculating a further resultant output
image pixel at said predetermined pixel position in 5 said output image by combining said first resultant
output image pixel and said third interpolated output image pixel as a function of said further input image characteristic value.

0 34. The apparatus according to claim 33, wherein said
resultant output image pixel is calculated according to the algorithm:

P = SX + (1 - S)Y
f.
where

P represents said resultant output image pixel;

0 X represents said first interpolated output image
pixel ;

Y represents said second interpolated output image
pixel ; and
5 S represents a scaling factor, with a value of from 0 to l, derived from said input image characteristic value,

and wherein

said further resultant output image pixel is
calculated by using the algorithm:

P1 = s'w + (1 - s')P

where P represents said further resultant output
image pixel; W represents said third interpolated
output image pixel and S represents a further
scaling factor with a value from O to 1, derived from said further input image characteristic value.

35. The apparatus according to claim 26, further
comprising a buffer containing a set of said first interpolated output image pixels and a set of said second interpolated output image pixels for accessing by said means for obtaining first and second
interpolated output image pixels to select one value from each one of said sets.