Color Matching System and Method

This invention relates to the color matching of video signals, and particularly to automatically matching the color signal to that of a pre-existing standard. This patent is a division of U.S. Pat. No. 4,679,067 whose disclosure is hereby incorporated by reference.

There is a continuing need to improve the efficiency, speed and accuracy of color matching of video signals, particularly in scene-by-scene color correction. It is an object of the invention to provide such improvement.

In accordance with an aspect of the present invention, a technique for color correction of video color signals is described wherein a first picture composed of color video signals is displayed on a monitor screen. Signals from a limited area on the screen which contain a specific color desiring to be corrected are sampled and stored in a signal storage area. A second picture is subsequently displayed on the monitor screen, which contains a limited area having the same color as in the limited area of the first picture. Signals from the limited area of the second picture are sampled and compared to the signals of the limited area of the first picture, which were recalled from the signal storage area. After completing the comparison, the signals from the limited area of the second picture are adjusted to agree with the color signals from the limited area in the first picture, thereby forming a color correction signal.

In another aspect of the invention, the color correction signal, obtained from comparing the sampled color video signals of a first picture to those of a second picture and then adjusting the color video signal of the second picture so as to agree with that of the first picture,is combined with the color video signals from the second picture thereby forming a color video signal which matches the color video signal of the first picture.

In yet another aspect of the present invention, the comparison between the sampled color video signals from a limited area in a first picture to that in a second picture consists of comparing the luminance signals and the hue and saturation values for the group comprises either red, green, blue, magenta, cyan or yellow, or I and Q. The comparison results are then used to develop correction values for the color video signals of the second limited area.

Preferably in this arrangement the sampling of the color signals is performed by either a window generator, a light pen, a touch-screen or such similar means. These means allow for easy selection of a limited area on the monitor screen which contain only the desired colored object whose color is sought to be matched. The use of these sampling means and automatic color matching greatly increases the speed at which video color corrections can be accomplished. For instance, if the balance achieved for one picture is suitable for use in others, it can be stored and reutilized, thereby further speeding the color correction process.

The foregoing and other objects and advantages of the present invention will be described and are apparent from the following description and drawings.

In the drawings:

FIG. 1 is a schematic circuit diagram of a color correction system constructed in accordance with the present invention;

FIG. 2 is a perspective view of an alternative component utilized in accordance with the present invention; and

FIG. 3 is a flow chart, in block diagram format, illustrating an embodiment of the present invention.

The invention can be used to great advantage in automatic color matching; that is, in automatically matching the color of a colored area to that of a pre-existing standard, so as to improve both the speed and quality of color correction. The full details of the system shown in FIG. 1 and the component shown in FIG. 2 have not been set forth in this description since they are described sufficiently in the patent mentioned above. Reference should be made to this patent for further details.

In this embodiment, it is preferred to use either a light-pen or a touch-screen to define a small sample area on the monitor screen. The operator places the light pen on the monitor screen at a location where the picture is supposed to be black. The machine automatically corrects the pedestal for R, G and B to the level sufficient to produce a neutral black. Then, the machine sequences automatically, or the operator presses a "gray" button (not shown) and locates the light pen in an area of the picture which is supposed to be gray, and the machine automatically compensates or corrects the gamma of R, B and G to give a neutral gray. Next, the machine sequences automatically, or the operator presses the white button and locates the light pen at a white portion of the screen, and the machine automatically adjusts the gain of R, B and G to give a neutral white. Then, the gain, gamma and pedestal correction signal values are stored for that frame or scene.

When a new scene is defined as in the Rainbow patent, the corrections are executed as described in that patent.

If there is a particular area of the scene for which a specific color is required to be stored, such as for the color of a product, or flesh tones of a person's face, or a blue sky, etc., a first "memory-select" button (not shown) is pressed. Then, the light pen is directed to that portion of the picture, and the full video levels, at that picture location, for yellow, green, cyan, blue, magenta and red signals are stored, and/or the values of I and Q signals are stored. The luminance value also is stored.

The same procedure can be repeated for each subsequent scene, or frame, or for a different specifically colored object in the same frame. When a particular object appears in a new scene which has appeared in a previous scene, a light pen is directed to that object and the trigger 271 (FIG. 2) on it is operated. The resulting signal from the light pen is used to form a small window which thereafter behaves in the manner described above for the window 98. Then, the luminance of the new object is compared with the luminance of the same object in the previous scene. If there is any difference between the two, the values of either I and Q, or red, green, blue, magenta, cyan and yellow are multiplied by the factor necessary to multiply the luminance to make the two luminances equal. Then, the resulting hue and saturation signals for red, green, blue, magenta, cyan and yellow, or I and Q, are compared with the prior values, and correction signals for each of the values are developed in the manner described in the reference patent for the automatic balance circuit. Then, the correction values are stored for that frame and used in the manner described above. In FIG. 3, an embodiment of this system is described using a flow chart.

Some of the advantages of this system and method are:

It allows unskilled operators to do accurate color corrections quickly.

The color corrections are much faster than in the past, even for experienced operators.

It allows the more skilled operators to be more accurate because they do not have to remember, from one scene to the next, what the color of a given item is supposed to look like. That is, for example, once the Eastman Kodak yellow is correct, the operator can repeat the color quickly for each subsequent scene in which it appears, without having to stop and make an independent judgment as to the correctness of the color in that scene.