TW526656B - Brightness nonuniformity correction method of the input equipment for unknown tone curve - Google Patents

Abstract

A brightness non-uniformity correction method of the input equipment for unknown tone curve is disclosed, which comprises: firstly, estimating the tone curve of the input equipment; then correcting the gray card image captured by the input equipment using this tone curve; storing the tone curve and the gray card image after correcting the tone curve as the tone curve of the input equipment and the gray card image after correcting the tone curve, so as to resolve the brightness non-uniformity problem of the image captured by the input equipment.

Description

526656 V. Description of the Invention (1) [Field of the Invention] The present invention is a method for correcting non-uniformity of an unknown tone curve input device, and is applied to an image input device, such as a digital camera, a digital video camera, and the like. [Background of the Invention] Generally speaking, when using an input device to capture an image, it often occurs that the captured image has uneven brightness, as shown in "Figures 1 A, 1 B, 1 C". The main reason is There are problems of uneven brightness caused by unevenness of ambient light sources, problems of uneven brightness caused by different angles of incident light entering the lens, and problems of uneven brightness caused by image sensing devices. In order to solve the aforementioned problem of uneven brightness, the following patents have been developed: For example, the US Patent No. 4 5 2 4 3 8 8 discloses a correction device. Card, and use the scanning value obtained by each pixel to correct the brightness unevenness of the captured image. Another example is the U.S. Patent No. 500 1 7 6 8 which discloses an image reading device, which is mainly used to scan the gray card with a uniform color and convert the scanned value of the gray card into LOG. Value, subtraction is used to replace the previous division operation, which makes the operation faster. For example, in the U.S. Patent No. 5 4 3 0 5 59 patent, an image reading device is disclosed, which mainly scans a gray card with uniform brightness to obtain the RGB value of each pixel, and then corrects R, G, and B respectively. The uneven brightness of each color plane

526656 V. Description of Invention (2). The aforementioned patents assume that the tone curve of the input device is linear, that is, the relationship between the actual brightness of the photographed image and the brightness of the image obtained by the input device is linear, as shown in "Figure 2A"; however, most image input devices The tone curve of is non-linear, as shown in "Figure 2B", that is, the relationship between the actual brightness of the photographed image and the brightness of the image obtained by the input device is not a linear relationship. When the tone curve of the input device is non-linear, the brightness information obtained using the shooting gray card cannot effectively remove the uneven brightness of the input image, especially the dark and bright parts of the image. Based on the above reasons, the present invention proposes an effective brightness unevenness φ correction method especially for input devices with unknown tone curves to solve the problem of brightness unevenness of input images. [Objective and Summary of the Invention] The main object of the present invention is to provide a method for correcting the brightness unevenness of an unknown tone curve input device to solve the problem of brightness unevenness of an image captured by the input device. According to the method for correcting the non-uniformity of the unknown tone curve input device disclosed in the present invention, the tone curve of the input device is first estimated; then, the tone curve of the image is corrected; then, the brightness of the image is equalized; and finally, stored Tone curve as the tone curve of the input device. In order to estimate the tone curve of the input device, the present invention discloses two methods for estimating the tone curve of the input device. One method is to use a single tone gray card, a color manuscript, and measurement data of the color manuscript to correct the brightness unevenness. Secondly, a multi-level tone gray card and the measurement data of the gray card are used to correct the brightness unevenness.

Page 5 526656 V. Description of the invention (3) The method for correcting brightness non-uniformity using the measurement data of a single-tone gray card, color draft, and color draft includes the following steps: First, estimate the tone curve of the input device, That is, the tone curve is estimated using the color image and the color measurement data. Then, the tone curve is corrected, that is, the tone curve of the gray card image and the color image is corrected by the aforementioned tone curve. Then, the brightness is uniformized, that is, the tone curve is used. The gray card image after the correction removes the brightness unevenness of the color draft image after the correction of the tone curve; and then uses the color tone image of the color draft image after correction of the tone curve and uniform brightness to generate the chromaticity value of each color block in the measurement data Color correction parameters, and use this color correction parameter to correct the chromaticity value of each color block, and then calculate the average error value of the color draft image and each color block φ in its measurement data, and determine the relationship between the average error value and the previous error value. When the error value is less than the previous error value, re-evaluate the tone curve and start the above process again from the modified tone curve When the average error value is greater than the previous error value, the tone curve is stored as the tone curve of the input device and the process is ended. The tone curve obtained at this time is the estimated tone curve and can be used to solve the input. The brightness of the image captured by the device is not uniform. The aforementioned method for correcting brightness unevenness by using a multi-level tone gray card and measurement data of the gray card includes the following steps: First, the hue is estimated by using a multi-level tone gray card image and the measurement data of the gray card. Curve; then, the tone curve of the multi-level tone gray card image is corrected by this tone curve; then, the brightness change information is extracted from the multi-level tone gray card image to generate a single tone gray card image after correction of the tone curve. The estimated tone curve and the resulting tone curve are corrected for a single tone gray card image for subsequent processing

Page 6 526656 V. Description of the invention (4) Use to remove the brightness unevenness of the input image. In order to further understand the purpose, structural features, and functions of the present invention, the detailed description is illustrated as follows: [Detailed description of the embodiment] According to the brightness unevenness correction method of the unknown tone curve input device disclosed by the present invention, The Λ method is applied to the correction device 1. This device 12 can be placed in the input device 2 or can be independently but selectively connected to the device 2, such as "Figure 3" and "4 As shown in the figure, the clothing system includes: a storage unit 11, an input unit 12, and an operation sheet π 1 3. The order that Yude uses the input device 2— & 1 week gray card image and color draft: Loss material and measurement data of color draft are captured daily, then the storage unit 11 is used to store the adjustment curve and the error value. Relevant data 'The initial value of the tone curve is estimated from the y draft image and color measurement data, and the sigh of the error value is infinite. Like cum? ： ： ： 3 T is provided for the data captured by the turn-in device 2-the gray card shadow has the soil sample shirt material and the color measurement data input into the storage unit ii ', and the aforementioned measurement data is provided by 耷 彩Department ,, head 丨 丨 抑 丄 r 丄. Measure the amount of clams obtained. The Tianyi Xingli measuring instrument is (such as a spectrum meter). It is used to obtain the relevant data from the health storage unit 11 and add different flavors to it. This system uses the tone curve of w to correct the two image data. The tone is positive, and then the gray card image after the tone curve correction is used to correct the color draft image after the tone curve has been corrected. 'Remove the unevenness of the brightness of the color draft image, and use the word curve to correct the brightness. The chromaticity of each color block in the colorized image

526656 V. Description of the invention (5) The value (such as RGB value) and color measurement data generate a color correction parameter to correct the color image, and compare the color measurement data with the previously corrected color manuscript with uniform brightness. An average error value is obtained for the chromaticity value of the image, and the magnitude of the error value between the average value and the storage unit 11 is determined. When the average value is less than the error value, the error value is set to the average value, and the color draft is used. The measured data and the tone curve are corrected and the brightness is uniform. The new tone curve is calculated with the previously corrected tone curve and stored in the storage unit 1 1 for the operation unit 1 3 to perform again. It is more suitable for the input device 2 Calculation of the tone curve; when the average value is greater than the error value, the tone curve at this time and the gray card image corrected by the tone curve are stored in the storage unit 1 1 to store it | as the tone of the input device 2 The gray card image after the curve and tone curve correction is used for subsequent removal of the brightness unevenness of the input image. In addition, when using the multi-tone gray card image captured by the input device 2 and the measurement data of the gray card, the storage unit 11 is used to store the relevant lean material of the color curve. The input unit 12 is used for inputting a multi-level tone gray card image captured by the input device 2 and measurement data of the gray card into the storage unit 11, and the aforementioned measurement data is provided by a color measuring instrument. (Such as: spectrum meter) measured. The arithmetic unit 13 is used for obtaining relevant data from the storage unit 11 and adding _ to calculate. The arithmetic unit calculates a tone curve by using a multi-level tone gray card image and measurement data of the gray card, and corrects the tone curve based on the tone curve. The tone curve of the gray tone gray card image is obtained by extracting the brightness change information from the multi-level gray card image to generate a single tone gray card image with a tone curve correction.

Page 8 526656

V. Description of the invention (6) The tone curve and tone curve correction unit of a single tone gray card shadow storage unit 11 is used as the tone curve and tone curve of the input device 2 and the gray card image immediately after it is for subsequent processing. Use when removing the brightness & Also: As shown in "Figure 5", according to the method for correcting the unevenness of the degree of the unknown tone curve wheeling device disclosed in the present invention, the method mainly uses a single tone captured by the input device of the ungraded tone curve Gray card image and color image data, and the color measurement data, this method includes the following steps: First, start this process (step 1 0 〇); ^ · After that, estimate the tone curve of the turn-in equipment (Step 1 〇!), That is, using the color image and color measurement data to estimate the tone curve of the input device, and set the error value to infinite; then 'correct the tone curve (step 1 〇2), also That is, the tone curve of the gray card image and the color draft image is corrected by using the aforementioned tone curve; then, the brightness is uniformized (step 103), that is, the gray card image after the tone curve correction is used to remove the color draft image after the tone curve correction. The brightness non-uniformity of this color is to remove the brightness non-uniformity of each color dimension of the color image. It is mainly corrected by the formula Γ 1, j = I i, j * (Wmax / Wi, j), where W l, j is the i-th column in the gray card image; the pixel value of row i, Wmax is the maximum pixel value in the gray-card image, I i, j is the i-th column in the Sero image The pixel value of the j-th row, and Γ i, j are the uniform brightness values; color correction parameters are generated to correct the color draft image (step 104), that is, the color draft image corrected by the tone curve and uniformized in brightness. Nakago

Page 9 526656 V. Description of the invention (7) The chromaticity value (such as RGB value) of the color block and the color measurement data are used to generate color correction parameters, and the color correction parameters are used to correct the color of each color block in the color image. And calculate the average error value (step 105), that is, calculate the correctness of the tone curve, use the chromaticity value of each color block in the color image to convert the chromaticity value of another color space CIELAB, and The chromaticity value of the measurement data of the previous color image is also converted into the chromaticity value of another color space CIE LAB, and the difference between the two is calculated using the following formula: AE * ab = ((L-Ll) 2+ (A-Al) 2+ (B-Bl) 2) 1/2, and judge the average error value and the magnitude of the error value (step 1 〇 6). If all the color patches are averaged by φ E * ab When the value is less than an error value (which is a preset error value with an infinite value), the error value is reset to this value (step 1 0 9), and step 1 1 0 is performed, but if the average error If the value is greater than the error value, the tone curve and the corrected tone card image are stored as the tone of the input device. The gray card image after the line and tone curve correction is used for subsequent removal of the brightness unevenness of the input image (step 1 07), and the process is ended (step 10 8), and the tone curve is estimated again (step 1 1 0 ), Use the color measurement data and the color curve image after the tone curve is corrected and the brightness is equalized, and re-estimate the tone curve with the tone curve in the step of modifying the tone curve (step 102), and call for setting this tone curve Into the tone curve of the input device, and return to step 102 to re-correct the tone curve of the gray card and color image using the tone curve at this time, and carry out the subsequent steps to estimate the tone that is more in line with the actual input device Curved tone curve.

Page 10 526656 V. Description of the invention (8) Therefore, the present invention can uniformize the brightness of this image when the next time the input device captures another image, so as to solve the uneven brightness of the image captured by the input device. problem. Of course, if you go from step 101 to step 102, you skip to step 107 to store the tone curve tone curve and the gray card image after the tone curve correction, and when the process ends, these steps are actually linear. The tone curve is changed to a non-linear tone curve. Therefore, the tone curve obtained in these steps is more in line with the actual tone curve of the input device than the linear tone curve in the conventional technology. However, in step 102 at this time, it is only necessary to use the aforementioned tone curve to correct the tone curve of the gray card image. As shown in "Figure 6", the brightness unevenness correction method of another unknown tone curve input device of the present invention mainly uses a multi-level tone gray card image captured by the unknown tone curve input device and the gray card. The measurement data is used to estimate the tone curve of the input device and to correct the gray card image after correction of the tone curve with brightness unevenness. This method includes the following steps: · First, start the process (step 2 0 0); , Estimate the tone curve of the input device (step 201), that is, calculate the tone curve using the multi-level tone gray card image and the measurement data of this gray card, and then correct the tone curve (step 2 0 2), that is, The tone curve of the multi-level tone gray card image is corrected by using the aforementioned tone curve; then, the brightness change information of each pixel in the multi-level tone gray card image corrected by the tone curve is captured to generate a single tone after the tone curve correction.

Page 11 526656 V. Description of the invention (9) Gray card image (step 203); and the tone curve and the single tone gray card image after the tone curve correction are stored as the tone curve of the input device and the tone curve after the correction. The single-tone gray card image is used for subsequent removal of the brightness unevenness of the input image (step 2 0 4); finally, the process is ended (step 2 0 5). Of course, the multi-level tone gray card used in this method can be divided into several equal or unequal color blocks in order by the center point of the gray card, and the color of each adjacent color block is not the same (such as "the first Figures 7A, 7B, and 7C "), or divide the gray card into several equal or unequal strip-shaped color patches, and each of the rut-shaped color patches can be parallel or non-parallel to the boundary of the gray card ( (As shown in "Figures 7D, 7E, 7F"). [Achieved effect] The method provided by the present invention can remove problems such as uneven brightness caused by an external light source, uneven brightness caused by a lens, and uneven brightness caused by an image sensing element, so as to enable input. The brightness of the image captured by the device can be uniformized, so that the image captured by the input device can more closely match the image obtained by directly viewing the entity. The above are only the preferred embodiments of the present invention, and are not intended to limit the scope of implementation of the present invention; that is, all equivalent changes and modifications made in accordance with the scope of the patent application for the present invention are within the scope of the present invention patent. Covered.

Page 526656 Brief description of the drawings [Simplified description of the drawings] Figures 1A, 1B, and 1C are schematic diagrams that cause brightness unevenness; Figures 2 A and 2 B are schematic diagrams of the linear tone curve and the non-linear tone curve; Figures 3 and 4 are the relationship between the correction device and the input device and the structure of the correction device; Figure 5 is the flowchart of the present invention; Figure 6 is another flowchart of the present invention; and Figures 7A, 7B, 7C, and 7D , 7E, 7F are the color block arrangement diagrams of the multi-level tone gray card of the present invention. [Illustration of Symbols] Correction device 1 storage unit 11 input unit 1 2 arithmetic unit 1 3 input device 2

Claims (1)

526656 6. Scope of patent application 1. A method for correcting brightness unevenness of an unknown tone curve input device, the method includes the following steps: estimating a tone curve of the input device; correcting the tone curve: using the estimated tone curve Correcting a gray card image captured by the input device; and storing the tone card and the gray card image after the correction of the tone curve are stored as the input device's tone curve and the gray card after correction of the tone curve, respectively. image. 2. The method for correcting brightness unevenness of an unknown tone curve input device as described in item 1 of the scope of patent application, wherein the step of estimating a tone $ curve of the input device is to use the same acquisition environment as the gray card image Next, an initial value of the tone curve of the input device is estimated from a color draft image captured by the input device and measurement data of the color draft. 3. The method for correcting the brightness unevenness of an unknown tone curve input device as described in item 1 of the scope of patent application, wherein the step of estimating a tone curve of the input device is under the same acquisition environment as the gray card image , Estimating an initial value of the tone curve of the input device from a color draft image captured by the input device and a measurement data of the color draft, and the step of correcting the tone curve further includes correcting the estimated tone curve to In the same acquisition environment as the gray card image, the step of the tone curve of one color $ draft image captured by the input device. 4. The method for correcting brightness unevenness of an unknown tone curve input device as described in item 1 of the scope of the patent application, wherein the step of estimating a tone curve of the input device is performed under the same acquisition environment as the gray card image ,by Page 14 526656 VI. Scope of patent application One color draft image captured by the input device and one measurement data of the color draft estimate the initial value of the tone curve of the input device, and the step of correcting the tone curve further includes the estimated The obtained tone curve corrects the tone curve of the color draft image. After the step of correcting the tone curve, the method further includes the following steps: Uniform brightness: The gray card image corrected by the tone curve is used to remove the tone curve corrected. The unevenness of the brightness of the color draft image is generated; a color correction parameter is generated to correct the color draft image: the color correction parameter is generated by using the measurement data of the color draft image and one of the color draft after the tone curve is corrected and the brightness is uniform, And correct the chromaticity value of each color block in the φ color draft image with the color correction parameter; calculate an average error value: calculate the error value of the chromaticity value of the color draft image and each color block in the measurement data, and make an error Calculation of the average value; confirm that the average error value is greater than an error value. 5. The method for correcting brightness unevenness of an unknown tone curve input device as described in item 4 of the scope of patent application, wherein the step of calculating an average error value is to convert the chromaticity value of each color block in the color image into another The chromaticity value of a color space, and the chromaticity value of each color block in the measurement data are converted into the chromaticity value of the other color space, and the error value of the two is calculated for the average calculation of the error value. _ 6. The brightness unevenness correction method of the unknown tone curve input device as described in item 5 of the scope of patent application, wherein the other color space is CIE LAB ° 7. The unknown tone curve as described in item 4 of the scope of patent application Brightness of input device Page 15 526656 6. The method for correcting the non-uniformity of the patent application range, wherein when the result of confirming that the average error value is greater than an error value is No, then perform the following steps: set the error value to the average error value; and Estimating the tone curve again ... Using the measurement data and the tone image after the tone curve is corrected and the brightness is uniformized, re-estimate the tone curve with the tone curve in the modified tone curve, and after performing the step of correcting the tone curve The next steps. 8. A method for correcting brightness unevenness of an unknown tone curve input device, the method includes the following steps: Estimating a tone curve of the input device: taking a multi-level tone gray card image captured by the input device And the measured data of one of the images to calculate the tone curve; modify the tone curve: use the tone curve to correct the tone curve of the multi-level tone gray card image; capture each pixel in the multi-order tone gray card image after the tone curve correction Brightness change information to generate a single tone gray card image after a tone curve correction; and storage: storing the tone curve and the single tone gray card image after the tone curve correction are stored as the tone curve and tone curve of the input device, respectively The corrected single-tone gray card image. _9. The method for correcting the brightness unevenness of an unknown tone curve input device as described in item 8 of the scope of the patent application, wherein the gray card is divided into a plurality of color blocks in order by their center points. 10. The brightness of the unknown tone curve input device as described in item 9 of the scope of patent application Page 16 526656 6. Scope of Patent Application Degree unevenness correction method, wherein the plurality of color patches are equal. 1 1. The method for correcting brightness unevenness of an unknown tone curve input device as described in item 10 of the scope of patent application, wherein the adjacent color blocks in the plurality of color blocks have different colors. 12. The brightness unevenness correction method of an unknown tone curve input device as described in item 9 of the scope of the patent application, wherein the plurality of color patches are unequal. 13. The method for correcting brightness unevenness of an unknown tone curve input device as described in item 12 of the scope of patent application, wherein the adjacent color blocks of the plurality of color blocks have different colors. 1 4. The method for correcting the shell unevenness of the unknown tone curve input device according to item 8 of the scope of patent application, wherein the gray card is divided into a plurality of strip-shaped color blocks. 15. The method for correcting brightness unevenness of an unknown tone curve input device as described in item 14 of the scope of patent application, wherein the plurality of stripe color patches are equal. 16. The method for correcting brightness unevenness of an unknown tone curve input device as described in item 15 of the scope of the patent application, wherein the plurality of stripe color patches are parallel to the boundary of the gray card. 17. The method for correcting brightness unevenness of an unknown tone curve input device as described in item 15 of the scope of patent application, wherein the plurality of stripe color patches are not parallel to the gray card boundary. 18. The method for correcting brightness unevenness of an unknown tone curve input device as described in item 14 of the scope of patent application, wherein the plurality of stripe color patches are unequal. Page 17 526656 6. Application for Patent Scope 19. As described in the method of brightness unevenness correction of unknown tone curve input device as described in Item 18 of the scope of application for patent, where the plurality of stripe color patches are related to the gray card The boundaries are parallel to each other. 20. The method for correcting brightness unevenness of an unknown tone curve input device as described in item 18 of the scope of patent application, wherein the plurality of stripe color patches are not parallel to the boundary of the gray card. Page 18