Molar pattern is a kind ofDigital cameraperhapsScannerAnd other equipment,Photosensitive elementThe high-frequency interference fringe is a kind of colored high-frequency irregular fringe that will appear on the picture.Molar pattern has no obvious shape rule because it is irregular.
Moire pattern is an optical phenomenon first discovered by French researcher Moore in the 18th century.
Basic concepts
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When thespatial frequencyWhen the spatial frequency of the fringe in the image is close to that of the fringe in the image, a new wave shaped interference pattern may be generated, namely the so-called moire pattern.The grid texture of the sensor forms such a pattern.When the thin strip structure in the pattern intersects the structure of the sensor at a small angle, this effect will also produce obvious interference in the image.This phenomenon is very common in some cases of fine texture, such as cloth in fashion photography.This moire pattern may be displayed by brightness or color.The measure to eliminate this interference is to use an anti aliasing filter (also known asLow-pass filter）However, this filter will reduce the resolution of the lens.Therefore, it is necessary to make trade-offs and compromises between moire pattern and resolution in this issue. Different models of cameras have different problems and choices.[1]
Fig. 1 Molar fringe
For the camera, if it is designed to be installed on the lenslow pass filter It will have a good effect, but it will affect the photosSharpness；For scanner, there is no good solution.aboutCRT displayFor example, it refers to the phenomenon of wavy color interference in the picture.It mainly occurs when the focus of the text is prominent, because the residual value of the electron beam affects the surrounding phosphors when the electron beam collides with the phosphor in the CRT display, causing interference.This problem can be solved by changing the focus value.But CRT moire isShadow maskThe inherent and inherent characteristics of the grid cathode ray tube cannot be completely eliminated, and can only be suppressed and mitigated within a certain limit (such as through the displayOSD MenuMOIRE elimination option in).
Production principle
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Figure 2 Illustration of moire photography
To put it simply, the moire isBeat outAn expression of principle.Mathematically, when two equal amplitude sine waves with similar frequencies are superimposed, the amplitude of the composite signal will change according to the difference between the two frequencies.The beat difference principle is widely used in radio, television and communication, for frequency conversion, modulation, etc.
Similarly, the beat principle also applies to spatial frequencies.The superposition of fringes with slightly different spatial frequencies will gradually shift due to the difference in fringe spacing and overlapping position, and will also form beat.
If the spatial frequency of the CCD/CMOS pixel of the photosensitive element is close to the spatial frequency of the stripes in the image, moire patterns will be generated.To eliminate moire, the lens resolution should be much smaller than the spatial frequency of the sensor.When this condition is met, it is impossible to have fringes similar to those of the photosensitive elements in the image, so there will be no moire.In some digital cameras, a low-pass filter is installed to filter the higher spatial frequency part of the image in order to reduce the moire, which will certainly reduce the image sharpness.If the pixel density of future digital cameras can be greatly improved, far beyond the lens resolution, moire will not appear.
Mitigation and elimination
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Fig. 3 Formation of Moore fringe
Technically, Moore fringe is the visual result of interference between two lines or objects at a constant angle and frequency. When the human eye cannot distinguish the two lines or objects, only the interference patterns can be seen. This optical phenomenon is Moore fringe.In naked eye 3D display, if the black matrix stripes on the display panel overlap with the stripes of parallax baffle or cylindrical lens grating, Moore stripes will be generated, which will seriously affect the viewing effect.[2]
The formation of Moore fringes can be illustrated with Figure 3, including a group of fringes with a spacing and another group of fringes with a spacing of b
To overlap the included angles, they will produce a series of intersections. If the distance between these intersections is short and cannot be distinguished by the human eye, they will form obvious Moore stripes when connected.[2]
Connect the intersections in different directions to get the width of the Moore fringe in different directions:[2]
Where n is a natural number.[2]
Only when the width of the Moore fringe is smaller than the minimum width that can be recognized by the human eye, can the human eye be unaware of it, or the width of the Moore fringe is larger than the general visual range of the viewer, so that the viewer cannot see it, can the adverse effects of the Moore fringe be reduced to a certain extent.[2]
In actual product manufacturing, Moore fringe is a very complex subject, not only related to a, b and θ, but also affected by the shape of the black matrix on the display panel, the pitch of the parallax baffle, the width and position accuracy of the fringe.But in actual production, the Moore fringe can only be controlled by adjusting the tilt angle θ.[2]
Display moire
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Moire effect refers to a kind of wavy cluster generated in the interference generated by two overlapping line shapes.It is the interference between the mask shape and the video signal;The scanning ripple comes from the interference between the horizontal line and the shape of the shadow mask.Ripples are displayed as waveforms on the screen. This phenomenon will be more obvious when the resolution of the display increases.[3]
Because the video signal is always changing, the problem of video ripple is difficult to solve.The scanning ripple depends on the horizontal scanning frequency. As long as the appropriate frequency is selected, this situation can be reduced.However, due to the wide scanning frequency range of the autoscan display, ripple effects may occur in some display modes.At present, some high-end displays are designed with advanced functions to eliminate ripple distortion.For displays without this function, the ripple effect can be reduced by adjusting the resolution.[3]
