Have you ever encountered such embarrassment? When debugging the large LED screen, the picture always fails to match the border, just like wearing a suit that is not fit. Last year, a shopping mall opened, and the 16:9 promotional video was played on the vertical screen at 9:16, and all the characters were pulled into bamboo poles.​Canvas positioning deviation directly ruined the entire opening ceremony​​。

The relationship between physical canvas and logical canvas

These two concepts are like human skeletons and clothes. If you get confused, something will happen.​​The physical canvas is the actual size of the display​, such as the common 3840×2160 pixel dot matrix. The logical canvas is the size of the material you import, and the proportions of the two must be strictly matched. The most outrageous mistake I have ever seen is to stuff 4K materials into a 1080P physical canvas, and the image was compressed so much that my mother didn't recognize it.

Here is a practical formula:​Logical canvas width = physical canvas width × (actual display area/full screen area)​​. For example, the display area of ​​the arc screen is 85% of the standard screen. If the physical canvas is 7680×2160, the logical canvas should be set to 6528×2160. This is how the ring screen of a certain auto show was set up last year, saving 42% of debugging time.

Coordinate positioning comparison table

Pay attention to the tips for setting up the stadium:​Using a ring coordinate system can reduce splicing seam error by 15%​​. The football field project that was renovated last month used this method to reduce the screen synchronization error from 8ms to 2ms, and there will be no more drags when athletes sprint.

Self-question and answer key questions

Q: How to set the canvas of the special screen without distortion?
A: First do the mask mapping of the physical canvas, and then use the quadratic surface algorithm to correct it. The wavy screen of a science and technology museum has established a three-dimensional coordinate system to perfectly fit the surface, increasing the debugging efficiency by 3 times.

Q: How to unify the coordinates when multi-screen linkage?
A: Set the main screen as the reference origin, and the subscreen adopts the relative coordinate offset. Remember to leave a 3-5 pixel overlapping band for each subscreen, so that the picture transition is more natural. There is a theater project that uses this trick to achieve millisecond synchronization of 12 screens.

Q: How to deal with emergency responses when a sudden black edge?
A: Temporarily create a virtual canvas extension area and set the black edge area as a transparent channel. Last week's concert encountered a card failure, so I used this method to complete it in 10 minutes. The audience did not notice that there were 3 columns of modules missing on the right.

I have been working on on-site debugging for more than ten years and have seen too many car accidents caused by canvas settings. The most profound thing is a government conference center. Because the coordinate origin is wrong, the leader's face always appears at the joints of the two modules. Later, when recalibrating, it was found that the construction team installed the control card by 180 degrees in reverse - so, canvas positioning is both a technical job and a careful job. Although the new screen now comes with intelligent calibration, it still has to rely on the master's experience value to support the situation at critical moments!

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