19th-century photography technique employed in novel data storage method
18 comments
·October 24, 2024oh_my_goodness
jazzyjackson
Here's the math in the cited paper... I feel like they're making an error of 35960 as 36kilobits instead of, yeah, 15bits ?
https://ieeexplore.ieee.org/document/9438269
If, in our previous example, the 4 wavelengths were to be selected from a palette of 32 different wavelengths, a single worfel location could store ~36 Kilobits of data. Thus, a 1 cm2 media with 10μ2 data locations (8μ2 worfels with 2μ spacing on all sides) = 1,000,000 worfels/cm2. For example, (32!/((32-4)! • 4!)) = 35,960 distinct states. (An analogous use of formula (1) is drawing a hand of 5 playing cards from a 52-card deck yields 2,598,960 distinct hands.)
Applying the 35,960-state permutation table for k=4 (i.e., superimposing 4 wavelengths per worfel), and drawing from a palette, N, of 32 different wavelengths, yields 35,960,000,000 bits (≈35.9 gigabits) per cm2; or 35.9 x (6.42 cm2 per square inch) ≈ 230.4 gigabits/in2. And so for an example of a 4″x5″ media (20 in2), 20 x 230.4 ≈ 4.6 terabits per 4x5 inch media.
oh_my_goodness
Thanks. I believe choosing from 35,960 possible states only takes 15 bits, not 35,960 bits. But it's late on a Friday.
jazzyjackson
Yeah, there might be one more combinatorial explosion, so they can choose one of 16 combinations with each of those 35960 combinations... breaks one's brain.
null
throwup238
> While working on one DARPA-funded project, Solomon stumbled upon a page in a century-old optics textbook that caught his eye. It described a method developed by noted physicist Gabriel Lippmann for producing color photographs. Instead of using film or dyes, Lippmann created photos by using a glass plate coated with a specially formulated silver halide emulsion.
This method of color photography is absolutely fascinating and resulted in some of the best color photographs of the early 20th century.
The Library of Congress has a collection [1] of plates by Prokudin-Gorskii who was hired by the Czar to ride around Russia on a train and photograph the country in the years before WWI and the Revolution. In the last couple of decades someone restored and digitally aligned each color plate so now we have nearly 1,500 relatively high resolution color photographs of imperial Russia. He took photos of everything from Emirs to peasant girls to Tolstoy and all the architecture and scenery in between.
[1] https://www.loc.gov/collections/prokudin-gorskii/about-this-...
jazzyjackson
Wow, reading the wiki article on Lippmann plates, sounds almost like a hologram - baking a diffraction pattern into glass that is then 'replayed' by white light. It puzzled me when it says one of the disadvantages was that the resulting plate could not be copied - like the optical effect doesn't work on film? I don't understand. Another citation regards this as a feature-not-a-bug, pointing to its use in security documents, apparently used on UK passports (identical hologram on all passports) and individuated holograms on new German passports. "Lippmann OVD" - optically variable device.
formerly_proven
Prokudin-Gorskii's images are fascinating, but he didn't use Lippmann plates. Gorskii took three images using red, green and blue filters. That was also much more practical, because I don't think you can reproduce Lippmann plates, while you can print a positive RGB image with CMY(K) dyes. That's why they're CMY after all (cyan absorbs red, magenta absorbs green, yellow absorbs blue).
jazzyjackson
This is the first I'm hearing about this lack of reproducibility, I can't make sense of it, you could always just take a picture of the resulting plate, no? Except color photos weren't a thing yet, so there just wasn't the technology at the time to make multiple copies?
throwup238
Thank you for the correction! I didn’t realize that there were multiple different plate emulsion methods.
swayvil
>19th-century photography technique employed in novel data storage method
TECHNIQUE and METHOD are synonymous terms (don't quibble). Does anybody else find it irksome to build a sentence this way?
Koshkin
Depends on the context, I guess. In some, a method can involve multiple techniques; some of these techniques can be borrowed from other, unrelated, methods. (You could say that a photograph is kind of data storage, but still.)
formerly_proven
> While Rosenthal was visiting the International Space Station headquarters in Montgomery, Ala., in 2013, a top scientist said, “‘The data stored on the station gets erased every 24 hours by cosmic rays,’” Rosenthal recalls. “‘And we have to keep rewriting the data over and over and over again.’”
This doesn't seem right to me, considering the amount and age of COTS hardware with a variety of flash-storage in them (Thinkpads, Nikon DSLRs etc.)
pcl
Perhaps the more precise phrasing would be that the data is corrupted within a short enough period of time that they need to rewrite every 24 hours to ensure validity.
IIRC the shuttle’s magnetic-coil memory was hardened explicitly to defend against this sort of corruption, with additional windings to maintain a stronger charge state than would be used within the shield of the atmosphere.
jazzyjackson
Maybe a bit gets flipped every 24 hours but yeah cosmic rays don't just erase a whole drive... bit of a case of telephone here tho, just relaying a moment of inspiration.
It's difficult to understand the math on the storage density. Four colors out of a possible 32 colors is about 15 bits of information, not 40,000 bits of information.[1] If it's 15 bits per pixel and 115M pixels, then the capacity is 1.7Gb, not 4.6Tb.
Maybe I've misunderstood the coding. Corrections are welcome.
[1] Crude overestimate, assume 5 bits per color for 20 bits per pixel. More accurate is log2(32 choose 4), which you can type into Google to get 15 bits.