# Screen aspect changes and masking



## Kekegenkai (May 11, 2021)

One of my projects planned this winter is to increase my screen size and possibly add a masking system. I just watched Guardians of the galaxy and noticed that the aspect ratio changed several times during the film. I know this isnt uncommon.
 https://showbox.bio/
Is there any way to work around this? Seems pointless to have masking or even a 235 screen at all for films like this.


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## Da Wiz (May 8, 2019)

If you think you need masking changes when the aspect ratio of a movie changes, most of these take place when certain complex action scenes are shot for IMAX while the rest of the movie is in 2.35/2.40:1. If you can't stand the change from full screen (or nearly full-screen 16:9) in some scenes while others are 2.35/2.40:1, your theater has WAY TOO MUCH LIGHT. In a properly dark theater with any decent projector (probably $3000 or more), this should not be an issue. Increasing screen size is fraught with danger. If the screen is being made larger but you are increasing the gain of the screen at the same time, you can introduce a ball-of-mosquitos effect caused by hot spots on the screen causing a hot spot with "boiling pixels" that make it look like a ball of mosquitos in the center of your field of view... if you move your eyes from the center of the screen where you were seeing a ball of mosquitos to the left side of the screen, the ball of mosquitoes moves with your shift in the center of area you are looking at. Furthermore: the SMPTE recommends at least 12 fL for 100% white on standard definition content. 20 fL is their highest luminance recommendation for 1080p standard dynamic range content. If your projector is said to have 1500 lumens and you change from a 90-inch diagonal screen to a 120 inch diagonal (about 103 wide), you will lose a HUGE amount of light in projected images. I did calibrations for 10 years and walked into home theaters where the peak white level was 7 or 8 fL because the owners were clueless about light level vs. screen size being an issue. Trust me on this, if you end up with 7 or 8 fL instead of roughly 16 fL (middle of the SMPTE spec of 12-20 fL), the images are going to suck. If you increase screen size without increasing lumens the projector can put up on the screen, you're chasing a false goal. 

If the aspect changes during playback, you either have to change the masking each time the aspect changes, or just stop worrying about it and enjoy the movie. Having masking perfect is not that big of a deal unless the projector has a dumb-ly high black level.


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## snowballus (Jan 8, 2022)

Huge amount of information! I thought the frames in the theater would change sometimes but I didn't realize


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