Facsimile and static presentation processing – Natural color facsimile – Color correction
Reexamination Certificate
1998-02-27
2001-07-31
Lee, Cheukfan (Department: 2622)
Facsimile and static presentation processing
Natural color facsimile
Color correction
C358S518000
Reexamination Certificate
active
06268940
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a procedure for maximizing the visual quality of an image as defined in the claims.
In addition, the present invention relates to an apparatus for maximizing the visual quality of an image as defined in the claims.
As the use of information networks is gaining ground and their data transmission capacity is increasing, increasing numbers of digital colour images are being transmitted across the networks. Images are sent into the network from various sources, using different equipment and various encoding and packing methods known in themselves. Moreover, the technical origin of the images is generally unknown to the receiver.
Due to errors caused by the operations performed on the image, such as encoding and packing, as well as errors generated in the data transfer medium, the visual quality of the image is often deteriorated as compared with its original visual quality. For this reason, methods for implementing the colour reproduction of an image have been developed to maximize the visual quality of the image. In an optimal case, the reproduced image reproduces the visual impression given by an error-free original image unchanged. In practice, however, this is not always possible. A basic reason for this is that the original image usually has a larger range of colours than is possible to reproduce. But even if all the colours in the original could be reproduced, creating a visual similarity would still be difficult. That is to say, current chromatics does not know any methods for quantitatively determining the colour impressions produced by normal images consisting of numerous fields of different colours and shapes.
Several methods for colour correction and calibration, for improving the visual quality of an image, are known in the art. A feature common to these methods is that the technical origin of the image is known or a “model” (a high-quality photograph) of the image exists. However, the technical origin of an image received e.g. over an information network is not known, and therefore the prior-art methods cannot be used to improve the visual quality of the image.
It is possible to improve the visual quality of an image by a manual method, whereby an operator processing the image makes observations about the original picture, an image displayed on a computer screen or printed out on a printer, and corrects the colour reproduction manually on the basis of his/her own observations and skill. However, processing an image by this manual method is a slow and laborious business and requires a skilled image processing operator. Moreover, manual image processing requires expensive machines which must be compatible with each other and calibrated to ensure e.g. that an image displayed on-screen visually corresponds to its printed copy.
SUMMARY OF THE INVENTION
The object of the present invention is to eliminate the problems and drawbacks described above.
A specific object of the present invention is to produce a new type of procedure for image processing which can be easily implemented and automated for use in the processing of large amounts of images.
A further object of the present invention is to produce an apparatus which can be used for the processing of an image being transmitted in an information network, a printing system or the like to optimize the visual quality of the image without significantly retarding its transmission.
An additional object of the present invention is to present a procedure which can be used for improving the visual quality of an image without special image processing skill.
As for the features characteristic of the present invention, reference is made to the claims.
In the procedure of the present invention, an image in electronic format, preferably a colour image, is processed. The image may be a packed one, obtained by packing methods known in themselves, e.g. methods employing the GIF or TIFF standard. According to the invention, the image is converted into a chromaticity coordinate format, preferably an Ls&agr; coordinate format, where L stands for lightness, s for colour saturation, and &agr; for hue angle. The Ls&agr; values are determined for the RGB values in
FIG. 1
according to predefined equations. The image can also be converted into a format employing a different coordinate system. After this, the greyness balance of the image is determined and compared with a standard observer's greyness balance preference. Based on this comparison, the greyness balance of the image is adjusted to make it correspond to the standard observer's preference. In connection with the adjustment of the greyness balance in a preferred case, the highest and lowest lightness values of the grey shades are determined, a probability model is used to determine whether the shades should be neutral grey and the whole image is shifted in the colour space so that the highest and the lowest values correspond to neutral grey. The purpose of this operation is to adjust the greyness balance of the image so that white will be perceived as white and black will be perceived as black to a maximum degree of “correctness”. Finally, according to the invention, the optimized image is converted from the chromaticity coordinate format back into its original format.
The colour reproduction of the image is optimized to make it correspond to a standard observer's preference. A visual processor has been taught a preference selected on the basis of a large number of images of various themes presented to a number of test persons. The visual processor adjusts the visual quality of each image to a maximum level. The teaching of the visual processor can be performed by a control parameter optimizing method of a neural network method.
The procedure of the invention, has several advantages as compared with prior art. The most important and most significant advantage is undoubtedly the fact that the procedure corrects the visual quality of the image automatically and independently of the source, in other words, the technical origin as well as the “correct” colour reproduction are unknown. Furthermore, the procedure can be implemented independently of hardware, which means that the display device or printer eventually used to reproduce the image need not be known. The procedure can also be provided with profiles of different output device groups or individual devices, and the procedure can be incorporated in individual output devices.
A further advantage of the present invention as compared with prior art is that the procedure can be easily standardized for use as a method of improving image quality in information networks. Moreover, the procedure can be applied for different types of display devices, including the cathode ray tube, liquid crystal display and electroluminescent display. Further, the procedure can be applied for different types of display control systems, including standardized computer screens and computer screens developed for special uses, as well as television screens employing the normal and HDTV standards. In addition, the procedure can be applied for different types of colour printer, including electrography, ink jet, thermal printers, electronic colour printing machines and other printing machines connectable to a computer.
In an embodiment of the present invention, the colour reproduction of an image is determined and compared with a predetermined colour reproduction preference of a standard observer and based on this comparison, the colour reproduction of the image is accentuated to make it correspond to the standard observer's preference. Preferably the colour reproduction of the image is accentuated by adjusting the global colour reproduction of the image to make it correspond to the standard observer's preference. Global colour reproduction means the colour reproduction in the entire image, in other words, at this stage of the procedure the colours in the entire image are crispened or accentuated.
In another embodiment of the invention, the colour reproduction of the image is accent
Laihanen Pekka
Saarelma Hannu
Lee Cheukfan
Teknillinen Korkea Koulu Graafisen Tekniikan Laboratorio
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