Lets say we have image of CD (from scanner). Can we technically read it? What DPI is needed?


4 Answers 4

(700 MB) / ((10 cm) * 10 cm) = 378 839 604 bits / (inch * inch)

(from google calculator).

You'd have to get a scan with at least 378 839 604 dots per square inch, or (roughly) 20000 DPI. Good home scanners have 1200 or 2400 DPI at most.

  • 4
    Plus enough contrast to actually tell a 1 from a 0. Theoretically possible, but basically. No
    – Earlz
    May 13, 2010 at 19:51
  • 1
    It's actually even higher than that, since CDs are round and the above calculation is for its containing square. Never mind the hole in the middle. Beyond this I'm out of my depth, but I think you'd need an even higher imaging resolution to be able to resolve all the transitions. Wouldn't the Nyquist-Shannon Sampling Theorem come into play here?
    – afrazier
    May 13, 2010 at 19:55
  • 2
    I suspect you'd need some kind of laser scanner of some description, maybe we could dismantle a cd-rom drive for something that might work...
    – Mokubai
    May 13, 2010 at 20:01
  • 3
    @Mokubai isn't a cd-rom drive already a kind of "laser scanner"?
    – Blorgbeard
    May 13, 2010 at 20:12
  • 1
    @sync: probably the same way you can read data “instantly” from a 1GB jpeg file. And that jpeg file has to be stored somewhere…
    – liori
    Nov 7, 2013 at 14:33

Additionally you'd have to use the right wavelength of light to emit and record... those pits are so tiny that you can only fit light of a certain frequency there- so a conventional scanner wouldn't work!

Bottom line being that you can consider "DVD drive" == "scanner" (it has the right frequency laser and reader) and "ripping software" == "software to create scan image"

So the technology exists already. I guess if you were really keen you could reconstruct that DVD reader data into an graphical format of some kind such as png or bmp. However it is much easier to use conventional "image" formats to encode and transmit the data.

Answer is "yes, sort of, but not the way you described it"


My guess is that old-style CDs (not newer DVD/BlueRay formats) might be able to be. I'd also have to guess (again) that it would require at least double the resolution in each (2D) direction as the amount of data stored.

If those guesses have anything at all to do with reality, it would be a VERY data intensive operation. Would be much easier to just pack up the bits with a CD reader, rather than store/transmit a scan. :-)

  • +1 for the insight. I believe DVDs can work, but BlueRay I believe uses a crystalline structure which must be read with a laser to figure out if it's 1 or 0
    – Earlz
    May 13, 2010 at 19:53

In theory a lot of things are possible. In practice - no.

Theoretically you could build a scanner (maybe) which would be able to do such an operation, only building it would cost so much more than just taking a CD player, that noone in their right mind would do a thing like that. Which leaves us with a conclusion again, that practically, it's not possible.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.