US 5,710,828 AGranted

Method and apparatus for converting a threshold matrix which is then used to binarize image signals

AssigneeFuji Photo Film Co., Ltd.

InventorMichinori Hashimoto

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Abstract

An image processing method that employs a threshold matrix to binarize image signals obtained by reading an image recorded on a film such as microfilm. A middle tone image brightness range, which corresponds to a middle or half tone image, is discriminated by referring a brightness histogram for image signals. The upper- and lower-most brightness values of the middle tone image brightness range are used to convert the elements of a threshold matrix in accordance with a predetermined conversion expression, and the converted threshold matrix used for binarization processing. Even if a film density variation occurs or if there is a background density change, binary conversion (a dithering process) can be performed, without deterioration of image quality, within a middle tone density area of, for example, a photograph.

Claims17

Dependent claims

An image processing method, for employing a threshold matrix to binarize image signals obtained by reading an image recorded on a film, comprising the steps of:

a) preparing a histogram that represents the number of pixels in relation to an intensity or brightness level of said image signals;
b) discriminating from the histogram a middle tone image brightness range corresponding a middle tone image;
c) converting individual elements of a reference threshold matrix by using uppermost and lowermost brightness values of said middle tone image brightness range to obtain a converted threshold matrix;
and
d) binarizing said image signals by said converted threshold matrix,
wherein at said step c), said individual elements of said reference threshold matrix are converted by an expression given below to obtain said converted threshold matrix;
A.sub.pq =a.sub.pq (U-L)/X+L
wherein
A.sub.pq :
individual elements of said converted threshold matrix;
a.sub.pq :
the individual elements of said reference threshold matrix;
U:
the uppermost brightness value of said middle tone image brightness range;
L:
the lowermost brightness value of said middle tone image brightness range;
and
X:
a number that is greater than (U-L) and smaller than N, where N is a number representing an entire range of gray scale levels that is read for said image, when said film is a negative film, or a number that is greater than 1 and smaller than (U-L) when said film is a positive film.

16 more elements

An image processing apparatus, which employs a threshold matrix to binarize image signals obtained by reading an image recorded on a film, comprising:

a) histogram preparation means for preparing a histogram that represents the number of pixels in relation to an intensity or brightness level of said image signals;
b) a discriminator for discriminating from the histogram a middle tone image brightness range including brightness levels corresponding to a middle tone image;
c) a matrix converter for converting individual elements of a reference threshold matrix by using uppermost and lowermost brightness values for said middle tone image brightness range to obtain a converted threshold matrix;
and
d) a binarizer for binarizing said image signals by said converted threshold matrix,
wherein said matrix converter converts said individual elements of said threshold matrix by an expression given below to obtain said converted threshold matrix;
A.sub.pq =a.sub.pq (U-L)/X+L
wherein
A.sub.pq :
individual elements of said converted threshold matrix;
a.sub.pq :
the individual elements of said reference threshold matrix;
U:
the uppermost brightness value of said middle tone image brightness range;
L:
the lowermost brightness value of said middle tone image brightness range;
and
X:
a number that is greater than (U-L) and smaller than N, where N is a number representing an entire range of gray scale levels that is read for said image, when said film is a negative film, or a number that is greater than 1 and smaller than (U-L) when said film is a positive film.

16 more elements

Dependencies are inferred from the claim text.