CN101674443B - A method for color correction of a projector - Google Patents

Abstract

The invention provides a method for correcting colors of a projector, comprising the following steps: using a light meter to adjust parameters such as aperture, exposure time and the like of a camera; comparing the projected image obtained by the camera with an original image, using a nonlinear optimization method to fit a luminosity response curve; using the luminosity response curve to correct the original image to obtain a high-quality projected image suitable for human eyes. The method has advantages that a method of computer software is used, the problem of the color difference in a single-projection display system or a multi-projection display system is solved, the quality of pictures and the visual effect are improved, expensive and complicated special optical apparatuses are not needed, at the same time, the number of the photos needed in a HDR method is greatly reduced (the HDR method needs to shoot ten images, the method of the invention needs one image); and the method has simple operation, easy practicality and strong extensibility.

Description

A method for color correction of a projector

technical field

The invention relates to a convenient and fast color correction method for projectors, which is widely applicable to the fields of virtual reality, military simulation, video conferencing, industrial design and other fields related to display technology, such as various projectors, and solves the problems of nonlinear response of the brightness of the projector itself, Problems such as changes in output color with time of use, color differences between multiple projectors, etc., realize low-cost, easy-to-implement, and easy-to-operate projector color correction.

Background technique

With the rapid development of virtual reality technology, people pay more and more attention to visual display. Perceptual and psychological studies have shown that people can easily perceive a 2% difference in brightness and a color difference brought about by a 2nm light wavelength change. However, for projection display technology, as the projector's use time increases, the color of the projector will become darker (this is related to the service life of the bulb inside the projector); the brightness response in a single projector is nonlinear; at the same time, due to The manufacturer, type, and service time of the projectors are different, and there will also be differences in brightness and color between projectors. Even for the same type of projector produced by the same manufacturer, there will be more or less differences. Therefore, correction methods for color differences in display systems such as projectors have emerged.

Color correction methods can be roughly divided into hardware optical equipment methods and software technical methods. The former is based on professional optical equipment such as photometers and spectroradiometers, and the latter is based on high dynamic range (HDR, high dynamic range) image technology. The main problem of color correction is how to obtain the brightness response (ITF, intensity transfer function) curve of the projector. Wallace et al. used a color illuminance meter to measure the color space of the projector, and determined the color mapping of the projector to the standard space through a non-parametric model. Majumder et al. used a spectroradiometer to measure the color characteristics of the projector, and established an RGB three-channel color lookup table to realize the mapping of the color space. The disadvantage of these two methods is that they depend on expensive professional optical equipment, the operation is complicated and the cost is high. Raij A et al. used HDR technology to sample the output luminance when the RGB value of the projector increased, and obtained some HDR images, and then obtained the approximate ITF curve of the projector. The disadvantage is that a large number of sampled images are required. In practice Difficult to apply. How to achieve low-cost, high-efficiency, and easy-to-implement color correction is crucial.

Contents of the invention

The purpose of the present invention is to solve the problem of color difference in a single-projection or multi-projection display system, improve the visual experience of the display system, reduce technical cost, and simplify the operation method.

The invention provides a method for color correction of a projector, which uses a light meter to adjust parameters such as the aperture and exposure time of the camera; compares the projected image acquired by the camera with the original image, and uses a nonlinear optimization method to fit the brightness response curve ( ITF curve for short); the original image is corrected by ITF curve to obtain a high-quality projection image suitable for human vision. By using this invention, the picture quality and visual effect are improved, the color difference of the display system is reduced, the use of expensive and complex optical equipment is avoided, and the number of photos required when using the HDR method is also greatly reduced (the HDR method needs to shoot Dozens of images, this method only needs one), simple operation and easy implementation.

1. As shown in Figure 1, the present invention is made up of 6 parts: light meter (1), projection screen (2), camera (3), computer group (4), display system (5) and calibration image (8) ; Wherein, the computer group (4) is made up of N computers (6) (N is a positive integer); the display system (5) is made up of N projectors (7); the calibration image (8) is stored in the computer (6) .

2. Implementation steps:

Step 1: the inventive method (100) part, obtains brightness response curve (abbreviation ITF curve), concrete steps are as follows:

Step 110: start;

Step 120: the computer (6) reads the calibration image (8);

Step 121: the computer (6) calculates the image coordinates (abscissa and ordinate) of each sampling point in the calibration image (8) (the number of sampling points depends on the color progression of the calibration image (8), ranging from 1 to 256);

Step 122: the computer (6) extracts its color value to be cast according to the image coordinates of each sampling point;

Step 130: The computer (6) projects the calibration image (8) onto the projection screen (2) for display through the projector (7), and obtains a projected display image;

Step 131: The light meter (1) faces the projector (7) in front of the projection screen (2), and the light meter (1) measures the ambient light; combine the exposure time read by the light meter (1) with the aperture Set in the camera (3);

Step 132: Use the camera (3) to shoot the projected display image on the projection screen (2), and obtain a projected image with a color difference from the calibration image (8), which is referred to as the projected image for short;

Step 133: the computer (6) calculates the corresponding coordinates of each sampling point in the projected image;

Step 134: the computer (6) extracts its color value in the projected image according to the corresponding coordinates of each sampling point in the projected image, and this color value is referred to as projected color value for short;

Step 140: The color value to be projected and the projected color value of each sampling point form a color value pair, and use these color value pairs to fit an ITF curve (this curve is the correspondence between the color value to be projected and the projected color value) ;

Step 150: Solve the inverse function curve of the ITF curve, and establish a color lookup table (this color lookup table is the correspondence between projected color values and to-be-projected color values).

Step 2: In the method (200) part of the present invention, real-time color correction is performed on the original image in the computer (6), and the corrected image to be projected is obtained, which is projected by the projector (7) and displayed correctly on the projection screen (2), Specific steps are as follows:

Step 210: On the computer (6), input the original image that needs to be projected on the projection screen (2) through the projector (7);

Step 220: the computer (6) reads the color value of each point in the original image, i.e. the projected color value;

Step 230: using the color lookup table of the ITF curve obtained in part (100) of the method to obtain the color value to be projected corresponding to the projected color value;

Step 240: Record the to-be-projected color value of each point of the original image to obtain the to-be-projected image, project the to-be-projected image onto the projection screen (2) through the projector (7), and display the corrected projected image.

The above-mentioned implementation steps can be implemented between the computer group (4) and the display system (5).

Beneficial effect

The purpose of the present invention is to provide a convenient and quick projector color correction method. Its advantage lies in the use of computer software to solve the problem of color differences in single-projection or multi-projection display systems, improve picture quality and visual effects, avoid the use of expensive and complicated professional optical equipment, and greatly reduce The number of photos required when using the HDR method (the HDR method needs to take dozens of images, this method only needs one), the operation is simple, easy to implement, and has strong scalability.

Description of drawings

Figure 1 is a block diagram of the projector color correction system. This figure is also an accompanying drawing of the abstract of the specification. Among them: 1 is a light meter, 2 is a projection screen, 3 is a camera, 4 is a computer group, 5 is a display system, 6 is a computer, 7 is a projector, and 8 is a calibration image.

Figure 2 is the calibration image.

Fig. 3 is a flowchart of the method of the present invention.

Figure 4 is a comparison chart of color correction effects. Among them: the first image is the image to be projected, the second image is the uncorrected projection result image, and the third image is the corrected projection result image.

Detailed ways

Step 1: the inventive method (100) part, obtains ITF curve, concrete steps are as follows:

Step 110: start;

Step 120: the computer (6) reads the calibration image (8);

Step 121: the computer (6) calculates the image coordinates (abscissa and ordinate) of each sampling point in the calibration image (8) (the number of sampling points depends on the color progression of the calibration image (8), ranging from 1 to 256);

Step 122: the computer (6) extracts its color value to be cast according to the image coordinates of each sampling point;

Step 130: The computer (6) projects the calibration image (8) onto the projection screen (2) for display through the projector (7), and obtains a projected display image;

Step 131: The light meter (1) faces the projector (7) in front of the projection screen (2), and the light meter (1) measures the ambient light; combine the exposure time read by the light meter (1) with the aperture Set in the camera (3);

Step 132: Use the camera (3) to shoot the projected display image on the projection screen (2), and obtain a projected image with a color difference from the calibration image (8), which is referred to as the projected image for short;

Step 133: the computer (6) calculates the corresponding coordinates of each sampling point in the projected image;

Step 134: the computer (6) extracts its color value in the projected image according to the corresponding coordinates of each sampling point in the projected image, and this color value is referred to as projected color value for short;

Step 140: the to-be-projected color value and the projected color value of each sampling point form a color value pair, and use these color value pairs to fit an ITF curve;

Step 150: Solve the inverse function curve of the ITF curve, and establish a color lookup table.

Step 2: In the method (200) part of the present invention, real-time color correction is performed on the original image in the computer (6), and the corrected image to be projected is obtained, which is projected by the projector (7) and displayed correctly on the projection screen (2), Specific steps are as follows:

Step 210: On the computer (6), input the original image that needs to be projected on the projection screen (2) through the projector (7);

Step 220: the computer (6) reads the color value of each point in the original image, i.e. the projected color value;

Step 230: using the color lookup table of the ITF curve obtained in part (100) of the method to obtain the color value to be projected corresponding to the projected color value;

Step 240: Record the to-be-projected color value of each point of the original image to obtain the to-be-projected image, project the to-be-projected image onto the projection screen (2) through the projector (7), and display the corrected projected image.

Claims (1)

1. a method for correcting colors of projector is characterized in that, its equipment needed thereby and performing step are as follows:

Equipment needed thereby: light meter (1), projection screen (2), camera (3), computer set (4), display system (5) and uncalibrated image (8); Wherein, computer set (4) is made up of N computer (6), and described N is a positive integer; Display system (5) is made up of N projecting apparatus (7); Uncalibrated image (8) is stored in the computer (6);

Performing step:

Step 1: obtain brightness response curve, concrete steps are as follows:

Step 110: beginning;

Step 120: computer (6) reads uncalibrated image (8);

Step 121: computer (6) calculates the image coordinate of each sampled point in the uncalibrated image (8), comprises abscissa and ordinate, and the number of sampled point depends on the color progression of uncalibrated image (8), and scope is 1 to 256;

Step 122: computer (6) extracts its color value to be thrown according to the image coordinate of each sampled point;

Step 130: computer (6) projects to projection screen (2) with uncalibrated image (8) by projecting apparatus (7) and goes up demonstration, obtains the Projection Display image;

Step 131: light meter (1) is preceding at projection screen (2), over against projecting apparatus (7), and light meter (1) measure ambient light; Time for exposure and aperture combination that light meter (1) is read are set in the camera (3);

Step 132: use the Projection Display image on camera (3) the shooting projection screen (2), acquisition and uncalibrated image (8) have the projected image of color distortion;

Step 133: computer (6) calculates each sampled point corresponding coordinate in projected image;

Step 134: computer (6) extracts its color value in projected image according to each sampled point corresponding coordinate in projected image, and this color value abbreviates the projection color value as;

Step 140: the waiting of each sampled point thrown color value and projection color value, and to form color value right, utilizes these color values right, simulates brightness response curve, and this brightness response curve is the corresponding relation of waiting to throw between color value and the projection color value;

Step 150: find the solution the inverse function curve of brightness response curve, set up color lookup table, this color lookup table is the projection color value and waits to throw corresponding relation between the color value;

Step 2: the original image in the computer (6) is carried out real-time color proofread and correct, the image to be thrown after obtaining proofreading and correct is projected in projection screen (2) by projecting apparatus (7) and goes up correct demonstration, and concrete steps are as follows:

Step 210: on computer (6), input need be projected in original image on the projection screen (2) through projecting apparatus (7);

Step 220: computer (6) reads the color value of every bit in the original image, i.e. projection color value;

Step 230: utilize color lookup table, obtain the color value to be thrown of projection color value correspondence;

Step 240: the color value to be thrown of record original image every bit, obtain image to be thrown, will wait to throw image projection to projection screen (2) by projecting apparatus (7), show the projected image after proofreading and correct.

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