Current practical methods for printing CGH

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Nnnn
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Current practical methods for printing CGH

Post by Nnnn » Fri Nov 08, 2019 6:36 am

As the topic says.

Are there any current methods for 'printing' computer generated holograms that are feasible for the hobbyist holographer at home?

As far as budget goes, I'm broke.

I'm aware of:
1) Photographic compression (print out the hologram on paper, take a picture on high-contrast 35mm film, and then the developed negative becomes the hologram. Works, but this is extremely low resolution)
2) Printing to a CDR - The tech exists, but was never made public. I'm personally working on trying to recreate this for DVD, but...
3) Modifying a projector into a SLM - I hear this is possible but it also sounds difficult as hell. Not sure if I have the technical prowess for this one, but I'm getting the feeling this is going to be the answer...

What else is there nowadays?

lobaz
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Re: Current practical methods for printing CGH

Post by lobaz » Fri Nov 08, 2019 3:28 pm

Hi, Nana,
as far as I know, there is no simple and affordable way.

You can find someone from the printing industry still operating an imagesetter. It will "print" you a binary opaque (black) pattern on a transparent film. The imagesetters pixels can be approximately 10 um in diameter, maybe a bit lower, but then they start to be quite unreliable. The diffraction angle you can get is very small, say about 2 degrees. It cannot give you a hologram suitable for 3-D observation, but you can test the principles.
You can also use an additional optics, e.g., a lens or a curved mirror, to make the angular extent of the reconstructed light wider. It will also make the image smaller, but there is no problem in "printing" the hologram larger - the films from imagesetters are not expensive, about 5 USD per A4 format.

Hacking a projector is possible, but the pixels you get are 10 um again. You will not get wider diffraction angle than from the imagesetter. You will be limited by the SLM size, say about 1-2 cm diagonal. But you can test your calculations instantly, which is good.

The CD writer you mentioned was done, as far as I know, once. They hacked the firmware of the CD-ROM and it worked just for that model. Once the CD-ROM drive was discontionued, it was gone.

If you have interesting results, you can contact Kyoji Matsushima and his Kan-dai studio CGH printing service. I do not know his pricing, but as it is non-commercial effort, moy may be lucky :)

By the way, what type of CGH are you going to make?

Petr

Nnnn
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Re: Current practical methods for printing CGH

Post by Nnnn » Sat Nov 09, 2019 7:00 am

Thank you for the in-depth reply! Do you know an imagesetting service that you can recommend? The ones I've seen seem to be pretty expensive/want large minimum orders.

As for the CDR drive, I've managed to track down and obtain the same model drive sakamoto et. all used for the experiment 20 years ago, but I couldn't convince them to share the firmware with me, lol. I found a certain dvd drive with similar capabilities though, so I'm working on hacking a certain burning software for it to see if I can get similar results.

I appreciate the info about Kyoji Matsushima! I will have a look.

As for what I'm going to make, just trying to learn about the medium so far ^_^. I would love to make some combined analog/digital art holograms in the future, though.

lobaz
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Re: Current practical methods for printing CGH

Post by lobaz » Sat Nov 09, 2019 9:56 am

I have no particular recommendation to the imagesetting device. About 20 years ago, you could find one in every medium size town. Today, they were largely replaced by CtP (computer-to-plate) technology. But imagesetters are still used in printing industry, for exampe in silkscreen printing or in die-stamping. Contact your nearest printing house or DTP studio and find someone older. I guess they will tell you where to find an imagesetter still in operation. I don't think they will be expensive or require minimum orders -- in fact, it is quite common to ask for a single sheet.
Once you find it, contact me for details how to prepare data.

I am not sure if you succeed with burning software hacking. I think you must go one level deeper, i.e., the drive firmware that actually drives the laser.

If you are still learning CGH, check my CDGH Tools at https://gitlab.com/petr.lobaz/CGDH-Tools

Petr

Nnnn
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Joined: Tue Nov 06, 2018 3:23 am

Re: Current practical methods for printing CGH

Post by Nnnn » Mon Nov 11, 2019 12:21 am

Thanks again for your help lobaz. I've been looking for a decent introduction to CGH for hobbyists since I learned about this medium, and finding your CDGH tools is what inspired me to try it out for real.

I'm not sure myself whether software hacking alone will be sufficient... I too feel I may have to write custom drivers to make this work, but I really don't know how to approach that. Sakamoto et. all were working directly with Yamaha, but unfortunately all of the Yamaha drives capable of disct@2 are not only no longer supported, but the people who were involved with the project are retired. orz

I've managed to change the drawing quality of images on DVD considerably (I think I am getting above 600dpi at least... good for fun, but obviously won't cut it for holography), but the question from here is exactly what scale of dots the software is sending to the drive, and whether or not the drive is internally scaling the coordinate planes it receives. In the miracle chance that it's 1:1, then software should at least be possible.

If anybody happens to have any acquaintances that worked on drives capable of Labelflash please send them my way. :roll:

I made a thread documenting a couple of my questions/research on this topic on another technology forum, but haven't gotten a single reply yet.
https://club.myce.com/t/writing-visible ... ray/405875

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thycore
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Re: Current practical methods for printing CGH

Post by thycore » Sun Dec 22, 2019 10:01 am

Perhaps some reverse engineering can be done on chimera process ?

https://www.ultimate-holography.com/chimera

lobaz
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Re: Current practical methods for printing CGH

Post by lobaz » Sun Dec 29, 2019 2:24 pm

Chimera process has nothing to do with CGH as discussed in this thread - as far as I know. The Chimera printer is just an evolution step in a well-known holographic stereogram production, the same as Geola, Zebra Imaging, XYZ, former Ultimate printers, etc. The construction is well described in, e.g., "Ultra-realistic imaging" by Hans Bjelkhagen and David Brotherton-Ratcliffe. The principle is simple - a small square (called a hogel) of a holographic plate is illuminated by an image formed on a micro-display and a reference wave. Thus, a hogel contains a small hologram of the image - for example, a reflection hologram. To make a big hologram, one has to expose thousands or millons of hogels.
Although the principle is simple, it is difficult to fine-tune everything and make the system reliable. The unique aspects of the Chimera system are a) very small hogel size (down to about 0.25 mm), b) U04 silver halide panchromatic material.

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