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Old 03-28-2012   #2
Tim Gray
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Tim Gray is offline
Join Date: Aug 2006
Posts: 1,869
RAW files from cameras are typically data before the demosaicing. If you look at a RAW file with no processing, it's got a checkerboard pattern to it and it's monochrome.

RAW files from scanners usually don't come from sensors with Bayer filters, so there's no RAW 'developing' (demosaicing) to be done. End of story. How they differ from TIFF output is they generally have a gamma of 1, and may or may not be inverted.

DNG is just a file format. You can put RAW data in it, before demosaicing. You can put RGB (demosaiced) data in them too. This is what linear DNGs are. Though it's just a file format, it doesn't mean that programs treat it the same as they would treat a TIFF file.

Vuescan will save your data as you wrote in many ways. TIFF, with Vuescan adjustments baked in and a gamma of ~2.2. TIFF DNG, with Vuescan adjustments baked in and I'm pretty sure a gamma of ~2.2. Or RAW DNG, no adjustments, gamma 1. Lastly, and I think the best, RAW TIFF: gamma 1, no funny file formats. All of the above are RGB data. The gamma 1 files aren't just untagged; they are gamma 1.

Programs like LR take DNG files with RGB data and a gamma of 1 and probably boost the gamma to ~2.2. Vuescan may or may not use that same ~2.2 when making the "TIFF DNG", but it does boost the gamma to something, which probably accounts for your brightness difference.

Frankly I think trying to cram in scanner files, gamma 1 or not, into LR and the like is a waste of time. Photoshop has all the tools you need to deal with a RAW gamma 1 scan file; LR doesn't necessarily. If you really need to edit your files in LR or ACR, they both accept TIFF files, so DNG doesn't offer a real advantage there. When I work with raw scan files, which is how I prefer to scan my color negs, the three most important things for me are 1) converting gamma 1 -> 2.2 properly, 2) setting the RGB black points properly, and 3) setting the RGB white points properly (less important than 2 in many cases). Setting white balance in the mid tones is a snap after that, as are regular contrast corrections, etc. By doing this stuff in LR, you trust #1 to the software (who knows what it's doing and giving up flexibility) and don't necessarily have the tools to do #2 and #3 properly.

The most 'raw' file format out of Vuescan is the RAW tiff file. Gamma 1, RGB data off the sensor, no color space attached. While the DNG RAW is nominally similar, programs don't necessarily treat DNG files the same as TIFF files and might/probably do some adjustments before displaying data (changing gamma, etc.). DNG wasn't really intended to be used for scanner data. TIFF is what you probably want; it's not unintuitive to store multichannel data, RGB or RGBI in this case, with an arbitrary gamma, usually 1, 1.8, or 2.2, in a TIFF file - that's what the format has been designed to do.
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