> There are even people out there who, using nothing but a compass with a
> sharp tip, cut patterns into acrylic glass to produce simple
> stereographic images (point clouds actually).
>
> And yes, it appears to actually work.

You can often see holograms in the paintwork of cars on a sunny day, it 
looks like an odd lens flare effect that is hovering some distance above 
the paintwork. It is caused by poor washing technique which drags grit 
across the paint creating tiny (but nothing like the wavelength of light 
tiny) grooves in the paint.

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On 23/12/2013 02:37 PM, scott wrote:
>> I also found a website with software for computing interference
>> patterns. They claim that if you take something like a 600 DPI laser
>> printer and print the pattern onto a transparency, you can shine a laser
>> pointer through it and get a very fuzzy, very grainy hologram.
>
> Oooh that sounds interesting, might have to give that a go. I got one of
> those cheap $20 green laser pointers, if you focus it it's enough to
> light a match or melt your name into anything plastic :-)

Knock yourself out:

http://corticalcafe.com/software_onlineCGHinstructions.htm

They demo it with a red laser; I don't know if that's crucial. (The 
laser wavelength is probably adjustable in the program...)

>> CD? Perhaps not; CDs don't use visible light, they use infra-red, so the
>> dot pitch might not be small enough.
>
> Well if a 600dpi print just about works, then by my rough estimations a
> CD should be about 20000 dpi. Maybe not perfect, but it works.

Yeah, I've been sat here trying to figure out what the actual DPI of one 
of these disks is. I guess it requires knowing how many inches per meter 
there are. :-P

>> A DVD, on the other hand, uses a
>> red laser, so it certainly ought to be able to do a red-light hologram
>> without difficulty. (Provided you can convince the drive to put the dots
>> where you want them!)
>
> You can't without modifying the drive. IIRC they had to bypass pretty
> much the whole signal path and just drive the laser directly (well not
> quite, but you get the idea).

Doesn't LightScribe help here? Or does that only allow you to specify a 
grey level, which the device itself then dithers?

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Am 23.12.2013 16:18, schrieb scott:
>> There are even people out there who, using nothing but a compass with a
>> sharp tip, cut patterns into acrylic glass to produce simple
>> stereographic images (point clouds actually).
>>
>> And yes, it appears to actually work.
>
> You can often see holograms in the paintwork of cars on a sunny day, it
> looks like an odd lens flare effect that is hovering some distance above
> the paintwork. It is caused by poor washing technique which drags grit
> across the paint creating tiny (but nothing like the wavelength of light
> tiny) grooves in the paint.

Yup, that's essentially the method they use for it - except that they do 
it on purpose :-P

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> Knock yourself out:
>
> http://corticalcafe.com/software_onlineCGHinstructions.htm
>
> They demo it with a red laser; I don't know if that's crucial. (The
> laser wavelength is probably adjustable in the program...)

Bookmarked - will definitely try that. I wonder if an ink-jet will work 
just as well...

> Yeah, I've been sat here trying to figure out what the actual DPI of one
> of these disks is.

I estimated 7e9 bits of data (probably an underestimate due to error 
correction bits etc) and an area of 17 square inches. sqrt(7e9/17) is 
about 20000 dpi.

> Doesn't LightScribe help here? Or does that only allow you to specify a
> grey level, which the device itself then dithers?

Maybe, but you'd probably still have to hack the hardware significantly 
to allow the lightscribe functionality to work on the data side of the 
disc at a much higher resolution.

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>> Knock yourself out:
>>
>> http://corticalcafe.com/software_onlineCGHinstructions.htm
>>
>> They demo it with a red laser; I don't know if that's crucial. (The
>> laser wavelength is probably adjustable in the program...)
>
> Bookmarked - will definitely try that. I wonder if an ink-jet will work
> just as well...

I suspect you'll find it nearly impossible to convince an inkjet to put 
the dots exactly where *you* asked for them.

>> Yeah, I've been sat here trying to figure out what the actual DPI of one
>> of these disks is.
>
> I estimated 7e9 bits of data (probably an underestimate due to error
> correction bits etc) and an area of 17 square inches. sqrt(7e9/17) is
> about 20000 dpi.

...or you could just look up the pit width figure from the spec sheet, 
and work out how many times that fits into an inch. ;-)

>> Doesn't LightScribe help here? Or does that only allow you to specify a
>> grey level, which the device itself then dithers?
>
> Maybe, but you'd probably still have to hack the hardware significantly
> to allow the lightscribe functionality to work on the data side of the
> disc at a much higher resolution.

That sounds like just a firmware nudge to me...

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