CN114152413B - Method and device for testing dynamic speckles in laser display - Google Patents
Method and device for testing dynamic speckles in laser display Download PDFInfo
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Abstract
A method for measuring dynamic speckle in laser display is characterized in that: the test method comprises the following steps: projecting a tested image onto a screen with a mark bit, enabling the shooting direction of a testing device to be vertical to the screen, focusing to be clear, collecting a first image, keeping the vertical distance between the testing device and the screen unchanged, and enabling the testing device to collect a second image after an image formed by the screen image on the testing device moves by using a moving device, so that an image collecting unit collects two images with the same testing area and different observation positions, wherein at least two images have a common testing area with the mark bit as a boundary; and performing image correlation processing calculation on the two pictures to finally obtain the dynamic speckle contrast. Compared with the speckle contrast static test method used in the current industry, the dynamic speckle contrast obtained by the method of the invention has higher accuracy, and can be widely applied to the speckle measurement of laser display products such as laser televisions, laser projectors, laser cinemas and the like.
Description
Technical Field
The invention relates to an evaluation and test method, belongs to the field of laser display performance test, and particularly relates to a test method and a test device for dynamic speckles in laser display.
Background
Laser display refers to a display technology using laser as a light source, compared with other display technologies, laser display has the largest color expression space, the color gamut coverage rate of the laser display can reach more than 90% of the color space recognized by human eyes theoretically, the laser display also has the advantages of high energy utilization rate, environmental protection, long service life, wide product coverage range and the like, the laser display is one of the display technologies with the greatest development prospect, and the market also presents a rapidly growing situation.
The laser is used as a narrow-band light source and has high coherence, after the laser is reflected by a rough reflecting surface (or penetrates through a scattering body), reflected (or transmitted) light waves are mutually interfered in a space nearby the rough reflecting surface to form granular fine spots with randomly distributed intensity and phase, namely laser speckles, and the speckle phenomenon can be often seen in an image displayed by the laser.
Laser display speckle is formed by multiple beam interference of reflected (or transmitted) laser light on a screen, and belongs to the category of statistical optics in principle because the intensity and phase of the speckle pattern distribution are randomly distributed. The displayed image will give a feeling of covering a layer of yarn if there is strong speckle. Speckle causes a decrease in resolution of laser display, unevenness in brightness and chromaticity, and eye fatigue, and needs to be suppressed. Speckle has been one of the major factors that have restricted laser display industrialization for a long time, and has not been completely solved yet.
Accordingly, a speckle testing technology must be established, earlier speckle tests are usually performed on simple devices built by researchers, and the test results of different units and different persons are greatly different. With the background that laser displays have entered a rapid development stage, standardized testing for speckle has become an urgent need. The International Electrotechnical Commission (IEC) issued international standards for two speckle tests, namely, "Optical test method for speckle contrast" (IEC 62906-5-2-2016 Laser Display Devices-Part 5-2 Optical measuring methods of spot contrast) "and" Optical test method for color speckle "(IEC 62906-5-4-2018 Laser Display Devices-Optical measuring methods of colour spot), in 2016 and 2018, respectively. National standards for speckle testing in China are also in preparation.
The speckle contrast C is a main evaluation index for speckle evaluation. The speckle contrast is defined as:
wherein C is speckle contrast, sigma represents light intensity standard deviation, < I > represents average light intensity of the image, and the calculation formulas of sigma and < I > are respectively as follows:
in the formula I i The light intensity at the ith point of the image is Nr, the pixel number of the image is Nr, and the calculation formula of the standard deviation sigma of the light intensity is as follows:
the larger the speckle contrast of the image, the more obvious the speckle phenomenon is.
At present, all the laser speckle display test methods are static, namely, a tested image is a static image, and laser display equipment and a test instrument are both in fixed positions, so that the method mainly has the following problems:
1. the microstructure of the screen greatly affects the speckle test. This is reasonable because speckle is the result of laser multi-beam interference, the screen microstructure determines the composition of the beam, determines that the test result is related to the screen microstructure; on the other hand, when an image without speckles is tested (incoherent light source illumination is used, such as a white light LED, the speckle contrast at the time is 0 theoretically), the prior art can still measure the speckles, which are caused by brightness fluctuation caused by a screen microstructure and are not speckles actually, the numerical value of the speckles can reach 6 percent, and the speckle test value is in the same order of magnitude as that of some laser projectors, so that the accuracy of the speckle test is seriously influenced;
2. influence of the picture pixel cell structure. At present, laser display mainly adopts a projection mode, a display chip of the laser display mainly adopts an HTPS-LCD (high temperature polysilicon), a DMD (digital micromirror), an LCOS (liquid crystal on silicon), an MEMS mirror and the like, a certain gap is usually formed between adjacent pixels of a display image, the gap is expressed as a dark line between the pixels, the dark line can be calculated as a dark area of speckle in a speckle test, the dark area has great influence on a test result, the influence is often up to 30 percent or even higher, and the influence must be eliminated;
3. the effect of brightness non-uniformity. The image projected by the laser projector always has a certain degree of brightness unevenness, and the brightness fluctuation of the image with uneven brightness can also be included in the calculation of the speckle.
Although some technologies have been developed to overcome the influence of the above problems, the universality is poor, some specific processing must be performed for the situation during image acquisition, and under the background that laser display is about to step into large-scale industrialization, universal and rapid speckle testing is a problem that the industry needs to solve urgently.
Disclosure of Invention
The invention aims to overcome the problem that the conventional laser speckle testing method is easily influenced by a screen microstructure, an image pixel unit structure and brightness uniformity, and provides a laser display dynamic speckle testing method and a testing device thereof with better universality and more accuracy.
The technical scheme adopted by the invention is a method for testing dynamic speckles in laser display, which is characterized by comprising the following steps: the test method comprises the following steps:
1) Starting laser display equipment, and projecting a tested image onto a screen to obtain a screen image;
2) The shooting direction of the testing device is vertical to the screen;
3) The method comprises the following steps of placing mark positions on a screen, wherein at least three mark positions are provided;
4) Slowly adjusting a lens of the testing device to focus the screen image until the testing device displays a clear image;
5) The testing device collects a first image;
6) Keeping the vertical distance between the testing device and the screen unchanged, and using a moving device to enable the image formed by the screen image on the testing device to move, then acquiring a second image by the testing device, so that an image acquisition unit acquires two images with the same testing area and different observation positions, wherein the two images at least have a common testing area taking a mark bit as a boundary;
7) Aligning the mark positions of the two pictures, intercepting the same test area, and calculating the standard deviation sigma of the dynamic speckles according to a formula D Standard deviation σ of dynamic speckle D According to the formula:
in the formula I i Is the light intensity of the ith point of the acquired first image, I i The light intensity of the ith point of the collected second image is defined, two points correspond to the same position of the screen image, and Nr is the pixel number of the tested image;
8) Using the formula
Calculating to obtain a value of dynamic speckle contrast, wherein<I>Is the average intensity of the same image or two images.
The laser speckle dynamic testing technology is researched and developed based on the following characteristics of speckles:
1. speckle is a statistical optical phenomenon of multi-beam interference, and is mainly characterized in that: the intensity variation of the speckle pattern conforms to the characteristics of random variables, and as an interference phenomenon, the speckle pattern is extremely sensitive to the variation of an observation position, and a small displacement of the observation position can cause the obvious variation of the speckle pattern;
2. the reflected light of the screen microstructure changes little for the observation position, and the screen microstructure before and after a little change (millimeter level) of the observation position is almost the same as that of the speckle; similarly, the pixel cell structure and brightness uniformity of the displayed image seen before and after a small change in viewing position (in the order of millimeters) is also nearly the same.
Accordingly, the image formed by the screen image on the testing device is displaced by a small amount through the moving device, and images observed at 2 positions before and after the position movement are respectively obtained. Composed of a screen, a pixel structure, andthe light intensity fluctuation generated by non-interference effects such as uniformity and the like forms the background of the whole image, and the intensity difference of the corresponding part of 2 images is very small; as a statistical optical phenomenon, speckle intensity distribution of images is completely random, speckle intensity distribution of 2 images is completely different, intensity at the same position of the 2 images is subtracted, an image background can be eliminated, speckle intensity signals are enhanced, speckle signals serving as random quantity are mutually superposed according to the principle of statistical optics, and average intensity of the speckle signals is the speckle of a single image
And (4) doubling.
Standard deviation sigma of dynamic speckle D Calculating according to formula (4):
in the formula I i Is the light intensity of the ith point of the acquired first image, I i For the light intensity of the ith point of the collected second image, the two points are corresponding to the same position of the screen image, and Nr is the pixel number of the tested image.
Dynamic speckle contrast C D Calculated according to the following formula:
the expression < I > is calculated from the first image (or the second image, or the average of 2 images, which are equivalent) using the expression (2).
The dynamic speckle contrast obtained by the method can eliminate the influences of screen microstructure, display image pixel structure and display image brightness nonuniformity, and the obtained test result is more accurate and has better universality.
Further design: the screen in the step 1) is a clean screen, stains and scratches which do not affect the speckle test are not generated on the screen, the whole test process is carried out in a dark room, and the marker bit in the step 3) is a standard cross.
And 5) 6) before the testing device collects the image, the testing device is in a vibration-free quiet state.
The three marker positions are three points of a right triangle respectively, and the marker positions can use standard crosses, so that the centering is convenient. The flag bit is used for determining the intercepted test area, and the test area is determined through the relative relation with the flag bit.
From the above description, it can be known that the dirt and scratch on the screen can affect the test result, and in order to prevent other light interference, the test process should be performed in a dark room, and the illuminance of the dark room for the test is below 0.1 lx.
The following test device is specially designed for realizing the test method of the dynamic speckles in the laser display:
a testing device for realizing a testing method of dynamic speckles in laser display is characterized in that: it comprises screen, mobile device, laser display equipment, testing arrangement, computer, and testing arrangement includes: the optical lens, the diaphragm, the light filter, the image acquisition unit, testing arrangement and computer carry out signal connection, the image transmission that shoots the image acquisition unit is for the computer, there is computational formula in the computer, the computer controls the image acquisition unit to carry out the shooting of speckle pattern, the diaphragm has been arranged from near to far away in the place ahead of image acquisition unit in proper order, optical lens, the light filter, after the light that laser display equipment throws the screen, the reflection is through the light filter, optical lens, the diaphragm gets into the image acquisition unit, mobile device is used for making the screen image pass through the image that optical lens becomes on the image acquisition unit and takes place the removal, thereby make the image acquisition unit gather two images that have the same test area, different observation position.
The image acquisition unit can be a CCD or CMOS image sensor, and the optical filter in the invention has the function of enabling the spectral response curve of the testing device to be consistent with the visual matching function curve of human eyes, and has to be used in the test of speckle contrast of color (composite color, such as white light), and the optical filter is usedY filter for matching the spectral response curve of the test device with the visual matching function of human eyes
In line, no filter may be used for the monochromatic speckle contrast test. When the optical filter is designed and manufactured, the transmittance spectrum curve of the optical lens and the spectrum response curve of the image acquisition unit are combined and calculated, so that the spectrum response curve of the whole testing device is matched with the visual matching function of human eyes
And (5) the consistency is achieved.
The computer of the invention stores a calculation formula (2) of the average light intensity < I > of the speckle pattern, and the formula is used for calculating the average value of the intensity of pixel blocks in all pixels of a speckle test area.
The processor of the invention also stores a calculation formula (4) for calculating the standard deviation of the pixel block intensity difference value corresponding to the same test area in the two speckle patterns, and the calculation formula is used for calculating the standard deviation of the pixel intensity difference value of the same position part in the two processed speckle patterns before and after displacement. Sigma D Is calculated according to equation (4):
where Nr represents the total number of samples, for example: using a 400 × 400 test window, then Nr is 160000,I i Representing the intensity of the ith pixel in the test window of the speckle pattern before a small amount of displacement, I i ' indicates the intensity of the ith pixel in the same test window of the speckle pattern after a small amount of displacement.
And formula (5):
the moving device moves the test device in a test plane parallel to the screen, so that the image of the screen image formed on the image acquisition unit through the optical lens moves, and the image acquisition unit acquires two images with the same test area and different observation positions. The test plane is parallel to the screen, the movement of the mobile device is full plane, and can be common horizontal and vertical translation, and also can be oblique line or curve movement, as long as two test positions are in the test plane.
The moving distance of the moving device does not exceed the diameter of the diaphragm.
The moving device is a swingable smooth glass sheet which is positioned between the optical filter and the screen, and incident light entering the diaphragm is changed by swinging the smooth glass sheet at an angle, so that an image formed by a screen image on the image acquisition unit through the optical lens moves, and the image acquisition unit acquires two images with the same test area and different observation positions. The incident light entering the diaphragm is changed by angularly swinging the smooth glass sheet, so that the same effect of the deviation of the incident light after the small displacement of the image acquisition device is achieved.
The plane of the swing central axis of the smooth glass sheet is parallel to the screen, and the smooth glass sheet is respectively positioned at the symmetrical position taking the swing axis as the center when the image acquisition unit acquires the images for two times. The plane of the swing shaft is parallel to the screen, and the swing shaft can be any straight line in the plane theoretically.
The swing angle of the smooth glass sheet is less than 20 degrees.
The testing method is ingenious, the equipment is simple and easy to manufacture, testing errors caused by the surface microstructure of the screen, the pixel unit structure of the image and the brightness uniformity can be well eliminated by the laser display dynamic speckle testing method, the speckle contrast value obtained by calculation is more accurate, a testing means is provided for the speckle condition of the laser display equipment, and effective reference is provided for one work of reducing or eliminating the speckle phenomenon.
Drawings
FIG. 1 is a flow chart of a method for testing dynamic speckle in laser display;
FIG. 2 is a schematic diagram of a testing device for dynamic speckle in a laser display;
FIG. 3 shows two positions of the test device for collecting images, where the moving distance of the test device is Δ d;
FIG. 4 is an example of an image obtained by two-time acquisition of a method for testing dynamic speckle in laser display;
FIG. 5 is a diagram of an embodiment of a method for varying incident light by rotating a smooth glass sheet to also achieve a small amount of displacement;
FIG. 6 is a picture projected by a laser projector with a distinct pixel structure;
fig. 7 is a picture of a laser projector projecting a significantly uneven luminance.
Wherein: 1 diaphragm, 2 image acquisition units, 3 optical lenses, 4 laser display devices, 5 optical filters, 6 screens, 7 testing devices and 8 smooth glass sheets
Detailed Description
The features of the present invention and other related features are described in further detail below by way of example in conjunction with the accompanying drawings to facilitate an understanding of those skilled in the art.
As shown in fig. 1 to 7, the technical scheme adopted by the invention is a test method of dynamic speckles in laser display, and the test method and the steps are as follows:
1) Starting laser display equipment and projecting a test image onto a screen;
2) The shooting direction of the testing device is vertical to the screen;
3) The method comprises the following steps of placing mark positions on a screen, wherein at least three mark positions are provided;
4) Slowly adjusting a lens of the testing device to focus the image, so that the testing device displays a clear image;
5) The testing device collects a first image;
6) Keeping the vertical distance between the testing device and the screen unchanged, and using the moving device to enable the image formed by the screen image on the testing device to move, then acquiring a second image by the testing device, so that an image acquisition unit acquires two images with the same testing area and different observation positions, wherein the two images at least have a common testing area with a mark position as a boundary;
7) Aligning the flag bits of the two pictures, intercepting the same test window area, and calculating the standard deviation sigma of the dynamic speckles according to a formula D Standard deviation σ of dynamic speckle D According to the formula:
in the formula I i Is the light intensity of the ith point of the acquired first image, I i For the light intensity of the ith point of the collected second image, two points correspond to the same position of the screen image, and Nr is the pixel number of the image in the tested area;
8) Using the formula
Calculating to obtain a value of dynamic speckle contrast, wherein<I>Is the average intensity of the same image or two images.
The following test device is specially designed for realizing the test method of the dynamic speckles in the laser display:
The shooting screen area is a clean screen, stains and scratches which do not affect the speckle test are not generated on the screen, the whole test process is carried out in a dark room, and the illuminance of the dark room for testing is below 0.1 lx. The marker positions arranged in front of the screen are standard crosses, and generally three marker positions are used, namely three points of a right-angled triangle. The flag bit is used for determining the intercepted test area, and the test area is determined through the relative relation with the flag bit. .
The image capturing unit may be a CCD (Charge-coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) image sensor, but is not limited to these two image capturing units, and in the process of capturing the color speckle pattern, the image capturing unit needs to satisfy the following conditions:
1. the image acquisition unit is a monochromatic sensor;
2. the pattern acquisition unit requiring the addition of optical filter should make the test device have the function of matching with the human eye color
The same spectral response curve;
3. the resolution of the pattern acquisition unit should be smaller than the image of the smallest speckle particle at the screen at the image acquisition unit to achieve accurate sampling of the speckle pattern.
After the image acquisition unit is selected as a CMOS, the detailed information of the speckle pattern shot by the CMOS unit is calculated so as to record related parameters.
The optical filter of the present invention is used for making the spectral response curve of the testing device consistent with the visual matching function curve of human eyes, and is necessary to be used in the test of speckle contrast of color (composite color, such as white light)
Consistently, the test for monochromatic speckle contrast may not be used. When the optical filter is designed and manufactured, the transmittance spectral curve of the optical lens and the spectral response curve of the image acquisition unit are combined and calculated, so that the spectral response curve of the whole testing device is consistent with the visual matching function of human eyes.
The computer of the invention stores a calculation formula (2) of the average light intensity < I > of the speckle pattern, and the formula is used for calculating the average value of the intensity of pixel blocks in all pixels of the area in the speckle pattern.
The processor of the invention also stores a calculation formula (4) and a formula (5) for calculating the standard deviation of the pixel block intensity difference value corresponding to the same test area in the two speckle patterns, and is used for calculating the standard deviation of the pixel intensity difference value of the same position part in the two processed speckle patterns before and after displacement. Sigma D Is calculated according to equation (4): where Nr represents the total amount of samples, for example: using a 400 × 400 test area, then Nr is 160000,I i Indicating the intensity of the ith pixel in the speckle pattern test area before a small amount of displacement, I i ' indicates the intensity of the ith pixel in the same test area of the speckle pattern after a small amount of displacement.
The test method comprises the following steps:
1) Firstly, starting a laser display device, projecting a detected image onto a screen, ensuring that the test of speckles cannot be influenced by stains and scratches in a shot screen area, and in order to ensure the test accuracy, carrying out the whole test process in a darkroom, wherein the darkroom illumination for the test is below 0.1 lx;
2) The method comprises the steps of placing a testing device at a proper position away from a screen to ensure that the shooting direction is vertical to the screen, placing an optical filter (generally a Y optical filter) in front of an image acquisition unit, wherein the optical filter has the function of enabling the spectral response curve of the testing device to be consistent with the visual matching function curve of human eyes and must be used in testing the speckle contrast of color (composite color, such as white light), the Y optical filter is usually used and has the function of enabling the spectral response curve of a testing system to be consistent with the visual matching function of the human eyes
In line, no filter may be used for the monochromatic speckle contrast test. When the optical filter is designed and manufactured, the transmittance spectral curve of the optical lens and the spectral response curve of the image acquisition unit are combined and calculated, so that the spectral response curve of the whole testing device and a person can be testedThe visual matching functions of the eyes are consistent;
3) In order to intercept the same test area, at least three marker bits are placed on the screen, the marker bits adopt standard crosses, and the three marker bits are respectively three points of a right triangle, as shown in fig. 3. The flag bit is used for determining the intercepted test area, and the test area is determined through the relative relation with the flag bit;
4) After the steps are prepared, slowly adjusting a lens of the testing device to focus the screen image until the testing device displays a clear image;
5) After focusing is finished, in order to eliminate the influence of vibration, the testing device is in a vibration-free quiet state before the testing device collects images, and the testing device collects a first image;
6) Keeping the testing distance unchanged, after the testing device integrally performs small displacement parallel to the screen, recovering the testing device to a silent state without vibration, and acquiring a second image by the testing device, wherein the small displacement means that the displacement distance does not exceed the diameter of the diaphragm, the diameter of the diaphragm is 17mm in the example, but the small displacement of the example is only less than 1mm. When the image acquisition device is displaced for a small amount, the displacement amount is as small as possible, so that the mark position on the screen can still be shot by the image acquisition unit after the small amount of displacement, and the invention is suitable for forming two front and rear speckle images which are completely different, and aims to reduce the influence on the experimental result caused by the nonuniformity of the image intensity shot before and after the displacement.
The moving device can enable the testing device to move in the testing plane, so that the image acquisition unit acquires images of the same testing area and different observation positions. The test plane is parallel to the screen, the movement of the mobile device is full plane, and can be common horizontal and vertical translation, and also can be oblique line or curve movement, as long as two test positions are in the test plane. The mobile device can be a mobile track, the testing device moves in the track and moves left and right relative to the screen to realize constant testing distance, and the testing device and a testing window intercepted by the marker bit have relative displacement; the moving device can also be a lifting device, so that the testing device relatively moves up and down with the screen to realize the constant testing distance, and the testing window intercepted by the testing device and the mark bit has a relative displacement.
As shown in fig. 4, in order to more accurately align the same test areas twice before and after a small amount of displacement, a cross mark method is used to assist the area alignment work twice before and after. Firstly, making cross mark points on a screen, and then shooting two pictures before and after a small displacement. The left image is an image acquired for the first time, the distance between the cross at the upper left corner and the left side of the image is Dc, the right image is an image acquired for the second time after small displacement, the distance between the cross at the upper left corner and the left side of the image is (Dc + delta d/m), m is the magnification ratio between the screen image and the image formed by the screen image on the image acquisition unit, and the displacement of the front image and the rear image is delta d/m. At this time, two 400 x 400 test areas at the same position are intercepted according to the relative position of the cross mark point. And then the image is transmitted to a computer for calculation.
The pixel area of the truncated test window is typically no greater than 1000 x 1000 pixels, but no less than 100 x 100 pixels. The test window is cut out in a rectangular, typically square, shape.
Example 2, as shown in fig. 5, the moving means is a swingable smooth glass plate 8, which is located between the optical filter and the screen, and the incident light entering the diaphragm is changed by swinging the smooth glass plate by a small angle so as to achieve the same effect of the deviation of the incident light after a small amount of displacement of the image capturing unit.
The plane of the swing shaft of the smooth glass sheet is parallel to the screen, and the smooth glass sheet is respectively positioned at different positions taking the swing shaft as the center when the image acquisition unit acquires images twice. The plane of the swing shaft is parallel to the screen, and the swing shaft can be any straight line in the plane theoretically. The angle of oscillation of the smooth glass sheet is <20 °, the angle of oscillation being as small as possible, in this case ± 8 °.
The specific implementation steps are that when the smooth glass sheet is in a solid line state and a first image is collected, the image that the reflected light r of the screen point A reaches the image collection unit through refraction of the smooth glass sheet (in a solid line position in the figure) is a, the smooth glass sheet swings to a second position, namely a dotted line position in the figure, the image that the reflected light r of the screen point A reaches the image collection unit through refraction of the smooth glass sheet is a', the image can be clearly seen in the figure, the image moves upwards, and a second image is collected. And intercepting two test areas which are not more than 1000 multiplied by 1000 and are positioned at the same screen position according to the relative relation of the cross mark position.
The rest of the composition which is not described is the same as that of example 1.
The implementation effect of the invention is as follows:
the following are several results of detection by using the dynamic speckle test method:
1. reduction of the influence of the screen microstructure: table 1 shows that the speckle contrast of different screens (including wall surface and white paper, which are often used as projection screens for convenience and economic reasons) should be 0 theoretically, i.e., "speckle" contrast under LED white light illumination, and the dynamic speckle contrast is significantly lower than that of the original image, thus achieving good effect.
TABLE 1 "speckle" contrast ratio under incoherent illumination of different screens
2. Reduction of pixel structure influence: fig. 6 is a picture projected by a laser projector and having an obvious pixel structure, the speckle contrast of the picture is 34.66, the value is obviously affected by a dark area of the pixel structure, after grid elimination processing is performed by adopting the prior art, the speckle contrast of the picture is calculated to be 5.67, and the value obtained by adopting a dynamic speckle processing method is 5.27, and the two can be considered to be consistent for a speckle test.
3. Reduction of influence of luminance unevenness: fig. 7 is a picture of the laser projector with obviously uneven brightness, the speckle contrast obtained by direct calculation for the original image is 24.97, the speckle contrast obtained by calculation after the prior art is adopted to eliminate the influence of brightness uniformity is 10.16, and the numerical value obtained by adopting the dynamic speckle processing method is 9.44, so that the uniformity of the two is better.
The following are specifically mentioned: in the two cases 2 and 3, the prior art needs a large amount of manual intervention work for processing, software is arranged in a very different way in the processing, the universality of the testing method is poor, and the dynamic speckle testing method does not need special processing, has good universality and is suitable for a large amount of tests.
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modifications and equivalents made on the basis of the technical idea of the present invention fall within the protection scope of the present invention.
Claims (10)
1. A method for testing dynamic speckles in laser display is characterized in that: the test method comprises the following steps:
1) Starting laser display equipment, and projecting a tested image onto a screen to obtain a screen image;
2) The shooting direction of the testing device is vertical to the screen;
3) The method comprises the following steps of placing mark bits on a screen, wherein at least three mark bits are arranged;
4) Slowly adjusting a lens of the testing device to focus the screen image until the testing device displays a clear image;
5) The testing device collects a first image;
6) Keeping the vertical distance between the testing device and the screen unchanged, and using the moving device to enable the image formed by the screen image on the testing device to move, then acquiring a second image by the testing device, so that an image acquisition unit acquires two images with the same testing area and different observation positions, wherein the two images at least have a common testing area with a mark position as a boundary;
7) Aligning the mark positions of the two pictures, intercepting the same test area, and calculating the standard deviation sigma of the dynamic speckles according to a formula D ：
In the formula I i Is the light intensity, I 'of the point I of the acquired first image' i The light intensity of the ith point of the collected second image is defined, two points correspond to the same position of the screen image, and Nr is the pixel number of the image in the tested area;
8) Using the formula
Calculating to obtain a value of dynamic speckle contrast, wherein<I>Is the average intensity of the same image or two images.
2. The method for testing dynamic speckle in laser display according to claim 1, wherein:
the screen in the step 1) is a clean screen, stains and scratches which do not affect the speckle test are not generated on the screen, the whole testing process is carried out in a darkroom, and the marker bit in the step 3) is a standard cross.
3. The method for testing dynamic speckle in laser display according to claim 2, wherein: and 5) 6) before the testing device collects the image, the testing device is in a vibration-free quiet state.
4. The method for testing dynamic speckle in laser display according to claim 2, wherein: the darkroom illumination for the test was below 0.1 lx.
5. A test apparatus for implementing the method of testing dynamic speckle in laser display according to claim 1, wherein: it comprises screen, mobile device, laser display equipment, testing arrangement, computer, and testing arrangement includes: the optical lens, the diaphragm, the light filter, the image acquisition unit, testing arrangement and computer carry out signal connection, the image transmission that shoots the image acquisition unit is for the computer, there is computational formula in the computer, the computer controls the image acquisition unit to carry out the shooting of speckle pattern, the diaphragm has been arranged from near to far away in the place ahead of image acquisition unit in proper order, optical lens, the light filter, after the light that laser display equipment throws the screen, the reflection is through the light filter, optical lens, the diaphragm gets into the image acquisition unit, mobile device is used for making the screen image pass through the image that optical lens becomes on the image acquisition unit and takes place the removal, thereby make the image acquisition unit gather two images that have the same test area, different observation position.
6. The device for testing dynamic speckle in laser display according to claim 5, wherein: the moving device moves the test device in a test plane parallel to the screen, so that the image of the screen image formed on the image acquisition unit through the optical lens moves, and the image acquisition unit acquires two images with the same test area and different observation positions.
7. The device for testing dynamic speckle in laser display according to claim 6, wherein: the moving distance of the moving device does not exceed the diameter of the diaphragm.
8. The device for testing dynamic speckle in laser display according to claim 5, wherein: the moving device is a swingable smooth glass sheet which is positioned between the optical filter and the screen, and incident light entering the diaphragm is changed by swinging the smooth glass sheet at an angle, so that an image formed by a screen image on the image acquisition unit through the optical lens moves, and the image acquisition unit acquires two images with the same test area and different observation positions.
9. The device for testing dynamic speckle in laser display according to claim 8, wherein: the plane on which the axis of oscillation of the smooth glass sheet lies is parallel to the screen.
10. The device for testing dynamic speckle in laser display according to any one of claims 8 or 9, wherein: the swing angle of the smooth glass sheet was <20 °.
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