2001.10.09 00:12 "Re: 16-bit ICC L*a*b* ?", by Martí_Maria
TIFF Lab of 16 bits are rare.. I do have only a couple, and if remember ok were from LaserSof'ts twain source and other form ScanOpenICC, I'm not shure of this latter.
8 bit ones are more common, and here Adobe ones exhibit an important difference... they are using D50 instead of D65. This makes the transport process easy, since, leaving aside the different encoding of a, b, the values does correspond to ICC PCS, and thus a 1:1 identity profile can do the trick.
About the profile... I did found a TiffLab8Spac.icm in an old torture-test sample from Microsoft, for Win95 ICM. I figure this profile is in public domain, since Microsoft put it available on their site. Anyway, the profile is easy to duplicate, it only does the a, b encoding translation plus a D65->D50 white point remapping.
16 bit TIFF in general are not very used, but there are some professionals using cameras like the Nikon D1, D1H, D1X that does use very low gamma to store the image preserving dark areas. They used to save in 16 bits to avoid the posterization effects by different gamma of display/printer. Humm.. gamma 1 should *never* be used, but this is like a "hard dump" of the camera memory.
Here 16 bits are needed. Also CMYK separations for high-end prepress are rendered to 16 bits on final stage on RIP, just because the dithering/blue noise stuff.
On the 16 bit Lab, well, this is another question. Lab has a enormous gamut, so converting from any 8 bit RGB to 8 bit Lab is for shure lossy. Just because Lab can contain a lot more values than any 8 bit RGB space. The image will be perceptually similar, but numbers will not match, and a images with bad gamma (1.0, for example) will lost a lot of information. So, Lab16 is required by numerical apps or precission color ones, not for "normal" imaging.
Of course, this is only my opinion and I could be wrong :-)
From: "Bill Radcliffe" <BillR@corbis.com>
To: "'Martí Maria'" <email@example.com>
Sent: Monday, October 08, 2001 1:32 PM
Subject: 16-bit ICC L*a*b*? RE:
Could you provide more details? Where are you seeing these 16 bit L*a*b* TIFF's coming from? Are these scanned files from particular manufacturers or ones that have come out of PageMaker or Photoshop? If they are coming from an Adobe product, I would expect them to provide an ICC profile that defines the color space.
Also - do you know what the status of 16-bit TIFF files is in general? Are you seeing more application of high bit depth scanning in your work? At the point that this becomes that standard way that people store files for archival, have an ICC profile based method for converting the images to 8-bit seems like a perfect match.
From: Maria [mailto:firstname.lastname@example.org] Sent: Saturday, October 06, 2001 7:33 AM Martí
To: Dwight Kelly; email@example.com
Subject: Re: 16-bit ICC L*a*b*?
To subscribe or unsubscribe email firstname.lastname@example.org with subscribe
or unsubscribe in the email body. Libtiff home page: http://www.libtiff.org
To subscribe or unsubscribe email email@example.com with subscribe or unsubscribe in the email body. Libtiff home page: http://www.libtiff.org