CD/DVD images.

[Sceadwian]

This is slightly off topic but has been a curiosity to me for a long time now. I'm sure most people have heard of lite scribe drives which use a special high powered laser to actually etch extremely high quality images onto the back of special CD-R discs.
I like a lot of people have also noticed that a CD/DVD-R that is written has a noticeble colour difference from a blanked section of disc. Now due to the way DVD's and CD's are encoded even a solid section of 0's and solid section of 1's won't look light or dark. So you can't write images that way, but if the encoding method is known you could come up with a special data set that would allow large parts of the media to be lightened or dark similar to the light scribe discs, but only on the data side of the disc.
It's obviously not practical, but I thought it might be interesting to figure out how to do this to come up with some readable text/graphics that will fit on say the last/first inch of a CD/DVD rom as a sort of data side label or signature.
Anyone have any tips or suggestions on takeing an ISO CD image and decoding a byte's position to it's absolute position on the disc and then writeing a special byte sequence that would make the entire area dark? This might be easier with CD's rather than DVD's because I know the actual physical layer bit encoding is very different.
Any advice or comments would be appreciated, especially if anyone has any links to the exact physical layer encoding methods of CD's DVD's (I'm too lazy to look them up right now)

 

[Marks256]

There is a substance on the label side of the disk that is sensative to the laser, the laser doesnt actually "inscribe" the image into the disk. If this photosensative material was placed on the data side, at least to the point where the data is still readable, then it should be possible.

 

[hjames]

I knew I remeber seeing this somewhere: Burning stuff into the data side of a CDR

**broken link removed**

Looks like it was a commercial failure though.

On a side note, those inner rings of the light scribe CDR's look like they'd make killer encoders. Reading them is a bit tricky mind you..

 

[Sceadwian]

That is exactly what I'm talking about, I can understand why it would be a commercial failure, I'm sure they would try to market the drives 25-50% more than a standard CD burner when all they're doing is bypassing the data encoder. No one would pay the premium, but since all drives are inherantly capable of doing it as long as the drives firmware allows certain CDROM protocols to be bypassed. It's also not very easy to see so the premium is even harder to justify.
Modern burners are able to read and write discs in raw data mode though, I'm wondering if it's possible to acount for the EFM encoding and specifically encode the data being sent to allow the bit patterns to become visable. Anyone know how feasable this is? I'm just not sure how capable the raw encoding method of a burner is, IE is it possible to actually bypass the EFM encoding method, or at least trick it so that you can send a bit pattern to it that will be encoded as a visible bit?

 

[Marks256]

He he, that is freaking sweet!

 

[The Mad Professor]

Hmm, now that has posabilities. As for compatability issues.. well I could not be any worse than trying to read Nero's InCD system lol.