Image analysis – Histogram processing – For setting a threshold
Patent
1986-08-05
1988-08-16
Boudreau, Leo H.
Image analysis
Histogram processing
For setting a threshold
340731, 382 56, G06K 936
Patent
active
047649755
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates generally to compression of image data, and, more particularly, to a method of and apparatus for compressing image data for use in displaying an image on a monitor or reproducing an image at a desired reproduction magnification based on image data obtained by photoelectrically scanning an original.
TECHNICAL BACKGROUND
It is well known in graphic arts to prepare color separation negatives or positives by applying predetermined processes to image data obtained by photoelectrically scanning an original by an image scanning and recording apparatus (hereinafter referred to as "color scanner"). In such a color scanner, since desired color corrections or gradation changes are made in processing electric image signals, it is necessary to display an image to be processed on a monitor or to simulate the image on a desired layout, in order to confirm processing results.
When displaying a desired image on a monitor, there is no problem when all the picture elements (hereinafter referred to as "pixels") of an original to be displayed are fewer than those of the monitor, but the original image cannot be displayed in its entirety on the monitor when all the pixels of the original image are greater than those of the monitor. For this reason, it is a general practice to either skip a predetermined number of pixels of the original image or to average the predetermined number of pixels thereof, by which the original image to be displayed is compressed to be adapted for display on the monitor.
In the case of skipping the predetermined number of pixels, however, it is difficult to display the image correctly on the monitor because a considerable amount of the original image is disregarded, which is very disadvantageous for graphic arts. On the other hand, U.S. Pat. No. 4,533,942 discloses a method of averaging a predetermined number of pixels of the original image, in which a desired number of pixels of an original image corresponding to one pixel of the monitor is processed as one block so that image compression with weighting may be carried out by evaluating or weighting respective pixels of the block. It is also described therein that image compression with uniformity can be carried out by averaging the pixels of the block.
In the foregoing averaging method, when a compression ratio is given in the form of 1
(where "n" is an integer), the image compression can be done by averaging the predetermined number of pixels of the original image, to convert the same into one pixel of the monitor. However, when a compression ratio is not given in the form of 1
, e.g., in the case that an original image having 1000 pixels is to be compressed into an image having 350 pixels which correspond to the entire pixels of the monitor, it is possible to effect the compression in an approximate integer compression ratio like 1/3. In this case, however, an image displayed on the monitor is relatively small in comparison with an effective area of the monitor. This is undesirable in the graphic arts, because it is necessary to display an image as large as possible throughout the effective area of the monitor, especially in modern graphic arts which often requires quite fine and minute corrections and changes of the image.
The aforementioned problems may be caused when a reduced image with a desired reduction ratio is reproduced from an original.
Accordingly, it is a primary object of the present invention to display an image on a monitor or to reproduce the image at a desired compression ratio and with high fidelity to an original, based on image data photoelectrically obtained from the original.
Another object of the invention is to ensure an image to be displayed as large as possible on an effective area of a monitor.
A further object of the invention is to simplify the hardware construction of the apparatus.
DISCLOSURE OF THE INVENTION
The aforementioned objects are accomplished by this invention, with an apparatus which comprises: compression data input means for inputting image compressi
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Boudreau Leo H.
Dainippon Screen Mfg. Co,. Ltd.
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