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Comment by dmitshur | Hacker News Reader

I've written about an unexpected outcome I've learned from this demo.

http://shurcool.wordpress.com/2011/10/06/the-effect-of-motio...

It does a lot to explain the discrepancies we often see when people argue "you can't see more than 24 frames per second" vs. "I can tell 60 vs. 120 fps".

It matters how DISTINCT the frames are.

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I was actually thinking about motion over the past few days. High frame rate does matter, but it's for a different reason. Human eyes can track objects extremely well.

Here's a simple test to do with the demo. Try tracking that motion-blurred cube on the left with your eyes - it's all blurry. Now, try tracking the one on the right - it will be sharp, but "jumpy". Now, try tracking the one on the right with your 120Hz monitor - the motion should be MUCH smoother - and that's where the need for high frame rates comes in. The higher the frame rate, the better the object will look when you're tracking it with your eyes.

Ideally, if we only account for objects travelling across the screen in 2 seconds, and a screen is ~2000 pixels wide, and we want to have an error of <=1 pixel, then theoretically, we need (2000px)/(2sec) = 1000 Hz frame rate for high motion realism. Unfortunately, I don't see it coming anytime soon...

So if the screen is really dense, say 20000px wide, you would need a 10kHz refresh rate. That contradict the contrast experiment.

In order to keep the increase in sharpness that you get from 10x the pixels - yes, you would need 10kHz, 10x the refresh rate. The moving picture would look sharper than the moving picture on the 2000px display. If you use 1000Hz refresh rate, then the crispness of moving objects on the 20,000px display would degrade to approximately the crispness of the 2,000px display. I hope that made sense.

This is a very good point, depending upon speed there's really no upper limit to the frame rate necessary for 'smooth' motion.

Also it's very, very annoying that Firefox is limited to 60Hz, that's very short sighted in my opinion.

Contrast definitely matters. The highest fps experiment that I've heard of was a researcher who had people dart their eyes left and right while looking at a strobing LED. They saw separate dots instead of a continuous line at strobe rates of up to 1500-2000Hz. That's probably the top-end of visual detection for a high-contrast, high-motion video.

On the topic of _distinct_ frames... I've made a simple tool [1] that specifically generates a sequence of highly distinct frames, which can be useful to do various tests on LCD/CRT monitors.

[1]: https://github.com/shurcooL/RefreshRateMultitool / http://hardforum.com/showthread.php?t=1423433

Btw, is it okay to plug your stuff? It's my first submission to HN so I'm not yet an expert on how things work here. I just thought it was relevant, so I wanted to share...

Have you tried reducing the frame rate in the demo to see if the same effect is true for 30 fps as well?

Also, I wonder if a simple square is enough to prove the "sameness" of motion blurs across different framerates. A fast camera pan across a landscape may yield different results.

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