8 bits vs 16 bits

[Ysarex]

Well clearly they're wrong then. 16 bit to 8 bit is 1/2 not 1/3 -- 16/8 = 2.........

16-bit is 2^16, while 8-bit is 2^8. Therefore, (2^16) / (2^8) = 65536 / 256 = 256. Working with a 16-bit image give you 256 times more data than an 8-bit image

Sparky has a hard number point here. That would be 4/10 of a percent then. My original rough estimate was way too generous. So we can now say that in the conversion from 16 bit to 8 bit we suffer a 99.6% data loss. It's hard to resist the numbers. If we take into consideration the loss from RAW to 16 bit and then the additional loss from JPEG compression it's perfectly clearly that in the conversion from RAW to JPEG with some perfectly reasonable rounding the data loss is 100%.

Joe

 

[Helen B]

Though it doesn't affect the results much, Photoshop works in 15-bit when set to 16-bit. You can see this in the info panel: the maximum value is 32768 (2^15).

 

[rambler]

"When you take a photo from Lightroom over to Photoshop for editing, by default, Lightroom makes a copy of the file (in TIFF format), embeds it with the ProPhoto RGB color profile, sets the bit depth to 16 bits, and sets the resolution to 240 ppi." Scott Kelby LR 3 Book, p. 250

"Adobe ...recommends choosing 16 bits for best results (although I {ie. Kelby} personally use 8-bit depth most of the time." p.250

 

[KmH]

Lets clear up a couple of numbers.

Today's DSLR's capture Raw files as 12-bit or 14-bit files, not 16 bit files. Raw converters add the extra bits to provide space for metadata, like the XMP line commands that are the edits in parametric Raw converters like Adobe Camera Raw (Camera Raw/Lightroom) and are not image data.

Bruce Fraser and Jeff Schewe also note in Real World Camera Raw that Photoshop's implimentation of 16 bits only uses 32,769 levels, not the fully possible 16-bit 65,536 levels. Just one advantage of doing so is 32,769 levels gives an unambiguous midpoint between pure white and pure black which is very helpful for operations like the different Photoshop blending modes that 65,536 levels doesn't offer.

Every edit we make reduces the the number of unique colors and tone levels in an image. That is worth repeating: Every edit we make reduces the the number of unique colors and tone levels in an image.

In fact, a good understanding how different types of edits impact an image helps one to decide where and how to apply edits.

This is where ACR (Camera Raw/Lightroom) and most other Raw converters have some serious limitations. The range of how to apply edits is so much more limited in ACR compared to the range of how to apply edit choices in CS5 or even Elements.

Real World Camera Raw with Adobe Photoshop CS5

Since Bruce and Jeff (Pixel Genius, LLC) also wrote the software for ACR's (Camera Raw/Lightroom) Sharpening tool, I also highly recommend - Real World Image Sharpening with Adobe Photoshop, Camera Raw, and Lightroom (2nd Edition) if you want to really understand sharpening.

And if you can swing it, get - Real World Color Management (2nd Edition)