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May 24,2021| LED Knowledge
Compared with traditional projection display, LED display has many technical advantages, such as larger dynamic brightness range, better brightness color uniformity, no graphic distortion, arbitrary size splicing, etc.
The LED display screen into the cinema application first needs to meet the certification of the DCI standard, the DCI organization by the world's six largest film companies jointly created, aimed to establish a unified digital film broadcasting standards, protect the digital film copyright and ensure the audio-visual experience of the cinema.
The DCI standard covers data form, codec interface, transmission mode, security guarantee, theater hardware system including server, projection, audio and control.
So, what are the LED specifications for DCI cinema LED displays?
1. Packaging selection of DCI cinema LED display screen
Due to the various sizes of movie screens in actual use, the DCI standard does not make mandatory regulations on the screen size, then corresponding to the 4K (4096 x 2160) fixed resolution of the screen, different screen sizes have different LED dot spacing, such as 2.5mm dot spacing for 10.3m wide small hall screen,
The 3.3mm dot spacing corresponds to the 13.5m-wide center hall screen.
For displays with this dot-spacing range, LED sizes are available from 10, 1616 to 2020 in a variety of packaging options.
Due to the setting of cinema viewing, it can ensure that even the first row of audience can not distinguish the pixels. Based on this premise, LED with the smallest package size should be selected to increase the proportion of the black panel or mask surface area in the whole screen area and improve the contrast.
2. Brightness requirements of DCI cinema LED display
According to the brightness requirement of 48cd/m2, the pixel spacing of 2.5mm, and the driving form of 30 sweep, the luminance of each LED is estimated to be 9mcd. According to the requirements of DCI white equilibrium point, the ratio of three primary colors is R: G: B = 20.9:72.2:
6.9. For a single LED, the R, G and B brightness requirements are 1.9mCD, 6.5mCD and 0.6mCD.
Such a luminance specification is far less than today's mainstream 1010 size LEDs.
It is true that the LED display control system can reduce the design brightness of the LED display to 48cd/m2 through gray level control, but it will bring many problems of low gray display, such as red color drift, uneven pixels, etc.
Due to the limitation of the minimum current specification of the driver chip, the current of the LED driver cannot be reduced indefinitely, which requires the LED to reduce the luminance through its own design, such as further reducing the chip size, or entering more light-absorbing particles in the package.
But it all comes at the expense of photoelectric efficiency.
If the minimum drive current of the drive chip can be further reduced or the number of scans supported can be further increased, the brightness of the LED display can be reduced without sacrificing photoelectric efficiency.
For LED itself, only when the proportion of R, G and B chips suitable for the color ratio of DCI white balance point is accurately selected, and the brightness that can meet the current requirements of the driver chip in the future is the LED that perfectly meets the application requirements.
3. Color requirements for DCI cinema LED display
According to the DCI-P3 color gamut defined by DCI, the R,G and B primary colors of the display screen have strict color coordinate requirements.
For LED display, LED needs to have strict color coordinate specifications.
However, at present, the vast majority of LED suppliers in the market define the color by the specification of the main wavelength, while the main wavelength is defined from one dimension (hue), missing the information of the other dimension (saturation) of the color.
Colors of the same primary wavelength correspond to a straight line in the color space that passes through an equal energy point (0.333, 0.333), rather than an exact color point.
Therefore, in order to accurately meet the color gamut requirements of DCI-P3, the LED with color coordinate definition should be selected first, rather than the imprecise definition of the main wavelength.
Due to the principle of display mixing, the initial design color gamut of the display screen can be equal to or greater than the color gamut of DCI-P3, that is, the initial design color coordinates of the three primary colors R,G and B need not be directly the color coordinates specified by DCI-P3, but can be the region formed by the bilateral extension lines and color space boundaries of each base point as shown in the figure.
Including green and blue, respectively is a similar to the small area of the triangle, due to the color of the LED discreteness, so the color of the small scope can hardly in a large quantity during to the LED, for the red, because the DCI - P3 is located in the base of color (100% saturation) space boundary, so in theory the possibility of LED, there is no meet.
These are the specifications of DCI Cinema LED Display.
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