"Holographic" Display with Rotating Blades

[Leo Liu]

Video:


I recently happened upon this holographic display design where a number of blades with led strips affixed rotate like a fan. It quite puzzles me how this such a design achieves the desired results. I am pretty confident that they use polar coordinates when mapping the pixels, but I am not so sure what the complete process looks like. What's more interesting is that several holographic can be put together to form a bigger display panel with some overlaps as shown in the video:



I suppose perhaps a few of PFers know a bit more about this type holographic display than I do. Please kindly explain how this bloody cool thing works. I would appreciate it.

 

[f95toli]

Assuming it works as advertised; it is quite a neat technology; although I struggle to see the point. Why not just use a regular display?

Also, in what way is this "holographic"?

 

[Leo Liu]

Assuming it works as advertised; it is quite a neat technology; although I struggle to see the point. Why not just use a regular display?

Also, in what way is this "holographic"?

I dunno; probably just an advertising trick. I have seen similar design used on a handheld fan which had embedded LED arrays ages ago. I assume this is just a scale up version of the fan I saw:

 

[berkeman]

Also, in what way is this "holographic"?

Yeah, I don't see any coherent light effects coming into play there...

 

[Tom.G]

I don't see any holographic effect there. It is just persistence-of-vision -- very much like a differing light patterns being projected on a screen can give the illusion of movement, that approach is commonly called a "Movie."

(Or in this computer age it is called a "Video.")

The images in the demonstration were most likely computer generated... that would be an awful lot of work to do manually!

Your skepticism is well founded, Well Done!

 

[tech99]

This seems to be a mechanical TV display, similar in principle to those used in the 1920s. It is almost transparent because we now use thin arms with tiny light emitters that are invisible once the device is rotating. Unfortunately the display has a motor in the centre, making it unsuitable for ordinary use. In the 1920s this device would have required a rotating switch for the row of lamps on each arm, which was impracticable.

 

[anorlunda]

This seems to be a mechanical TV display, similar in principle to those used in the 1920s. It is almost transparent because we now use thin arms with tiny light emitters that are invisible once the device is rotating. Unfortunately the display has a motor in the centre, making it unsuitable for ordinary use. In the 1920s this device would have required a rotating switch for the row of lamps on each arm, which was impracticable.

This?

 

[sophiecentaur]

Also, in what way is this "holographic"?

It's not a true hologram but the fan blades occupy a three dimensional space (it appears) and are not co-planar so, unlike a 2D projection screen, it can place pixels in three dimensions by suitably switching on at the right location in 3D space.

To me, the system seems to work like this: If a three dimensional object is sampled at places where there happens to be an available pixel on one of the fan blades at the appropriate time then an image will be formed from samples. This would be pretty non-trivial because the sampling of the 3D moving image won't be regular (nothing inherently wrong with that). The display just produces flashes of light (samples) at the right time and place corresponding to the appropriate part of the original image. The eye will just see an image which it interprets as 3D. Unfortunately the fan in the video is shown with its axis of rotation pointing at the camera so the conical motion can't be seen.

The clever bit is that the displayed image is three dimensional and can be viewed from a range of angles - just like a hologram. As soon as I saw it, I thought of the 'hologram' display of the Princess on the table in the first film of the series to be screened.

This seems to be a mechanical TV display, similar in principle to those used in the 1920s.

Yes - but the display occupies a 3D space so it can produce a 3D image.

The images in the demonstration were most likely computer generated..

Eventually they could be 'standards converted' from a suitably scanned object ( what we used to refer to as 'seller's material'). The intermediate stored image file would have all the information about the scene / object, having been fed in from one standard and displayed on another standard by transforming the co ordinates. Just requires loads of computing power.

I think I'm impressed.

 

[tech99]

Yes, I also had the pleasure of meeting Victor Miles, who built the equipment for Baird. The first successful display used 12 flashlight bulbs around a disc, powered by a 10 watt audio amplifier. Such an amplifier was expensive and difficult in the 1920s. In the camera which is in the photograph, the light is chopped by a slotted disc. This was intended to avoid a DC component on the video, as the selenium cells then used had a very poor high frequency response. The equipment was the first to display a motion picture with half tones, as previous attempts had given black and white images.

 

[phinds]

Unfortunately the display has a motor in the centre, making it unsuitable for ordinary use.

I don't get why. The last two objects the complex red one and the orange slices show no sign at all of anything in center that is not part of the image. That does make me wonder if the whole thing is a put-on.

 

[Hornbein]

Back in 1975 or so BBN made a projector with a mirror that vibrated in such a way that it changed its focal length. They were able to make truly 3D images that you could reach into.

 

[sophiecentaur]

That does make me wonder if the whole thing is a put-on.

Could be but that would spoil our fun. The apparent resolution is better than the spacing of the blades suggests - but maybe the images were chosen for best effect.
You'd wonder about the Health and Safety aspect of it all, with all those whirring blades. And wouldn't it be creating a massive draught?

 

[sophiecentaur]

Why not just use a regular display?

This system - even if it's only 2D - will show images of objects in front of what's actually behind them. There would be contrast issues, perhaps, due to the background being regularly obscured by the blade thickness. I could think of several applications.

 

[Hornbein]

Could be but that would spoil our fun. The apparent resolution is better than the spacing of the blades suggests - but maybe the images were chosen for best effect.
You'd wonder about the Health and Safety aspect of it all, with all those whirring blades. And wouldn't it be creating a massive draught?

The blades are flat and thin so they will move only a little air. If it were ever to become a consumer product there would be a safety problem. (I refuse to write "issue.")

 

[sophiecentaur]

show no sign at all of anything in center that is not part of the image.

Whilst the demo is starting up, you can see that there are LEDs in front of the motor / shaft. As long as there is some part of the image at or near the centre there would be no impairment. A 'hole' the centre of the image could reveal the shadow of the motor (and also the supporting frame).

 

[tech99]

If we use a scanning system which is circular there is always the effect of the eye looking at the centre, like a target, and this was rejected for ordinary TV purposes, but useful for other displays.