Vuescan Raw files: DNG or TIFF

[Rider]

You can output a raw film with the file already Infrared cleaned by using the Raw Save film option.

Thanks for pointing that out. It's very subtle!

[Greg Miller]

DNG is a open source RAW format created by Adobe. The rationale was to have a non-proprietary RAW format (as opposed to the many proprietary RAW formats that the camera manufacturers like Canon and Nikon have created) - so in theory 100 years from now you could still open a DNG file and process it where proprietary formats rely on the camera manufacturers to still be around since they do not divulge all of the details of their formats (although most people are not bothered by the fact that ACR processes proprietary RAW formats without knowing the full details of the format - Adobe basically reverse engineers the the format)

In theory, DNG should be better than TIFF since the DNG file would be unprocessed and you can perform processing such a color balance and contrast that is non-destructive. A TIFF file already has RGB values assigned so you are limited in the extent of processing that you can do. I do not know if Vuescan is using the full capabilities of DNG so the actual benefits may or may not exist in reality.

[domaz]

In theory, DNG should be better than TIFF since the DNG file would be unprocessed and you can perform processing such a color balance and contrast that is non-destructive. A TIFF file already has RGB values assigned so you are limited in the extent of processing that you can do. I do not know if Vuescan is using the full capabilities of DNG so the actual benefits may or may not exist in reality.

Greg what do you consider the full capabilities of DNG? Vuescan puts unprocessed RGB image data from the scanner in DNG similar to what a Camera's CCD/CMOS woud output. DNG does have the ability to do some complex stuff like embed various Image transform functions so the viewing program knows how to best interpret the data. One example in the DNG spec is the WarpFishEye transform that tells the viewer to "unwrap an image captured with a fisheye lens and map it instead to a perspective projection". So DNG can do some very interesting things but does a Scanner need to take advantage of this? I doubt it. Also remember that DNG is actually a TIFF 6.0 file at it's heart. TIFF is known as "thousands of image file formats" for good reason. So the difference between a Vuescan RAW TIFF and RAW DNG is probably very minimal.

[Greg Miller]

Greg what do you consider the full capabilities of DNG? Vuescan puts unprocessed RGB image data from the scanner in DNG similar to what a Camera's CCD/CMOS woud output. DNG does have the ability to do some complex stuff like embed various Image transform functions so the viewing program knows how to best interpret the data. One example in the DNG spec is the WarpFishEye transform that tells the viewer to "unwrap an image captured with a fisheye lens and map it instead to a perspective projection". So DNG can do some very interesting things but does a Scanner need to take advantage of this? I doubt it. Also remember that DNG is actually a TIFF 6.0 file at it's heart. TIFF is known as "thousands of image file formats" for good reason. So the difference between a Vuescan RAW TIFF and RAW DNG is probably very minimal.

Well, if it were a RAW file coming form a digital camera, then a huge advantage to the RAW file is that color balance, lightness, saturation, contrast,... can be changed radically with much fewer consequences than a tiff file because the data has not been associated with a specific RGB color space (e.g. Adobe RGB) . That cannot be said for a tiff file with the the data having been converted to RGB values.

While DNG does use a tiff structure at its foundation, that does not necessarily mean the data had been converted to RGB. DNG is certainly capable of storing non RGB data same as it is structured in a proprietary RAW format, maintaining the RAW file's ability to be adjusted for color balance, lightness, saturation. contrast,...

Again, I do not know much about how Vuescan creates the DNG file, so I am speaking in hypothetical terms. If the data Vuescan provides is similar to a digital camera's RAW file, then this is a significant advantage over a tiff file.

[Ben Syverson]

The "raw" DNG file that Vuescan produces is the same as the TIFF file, data-wise. It's just a question of whether the software you are importing to prefers DNG or TIFF.

There is no advantage to either.

[domaz]

Well, if it were a RAW file coming form a digital camera, then a huge advantage to the RAW file is that color balance, lightness, saturation, contrast,... can be changed radically with much fewer consequences than a tiff file because the data has not been associated with a specific RGB color space (e.g. Adobe RGB) . That cannot be said for a tiff file with the the data having been converted to RGB values.

While DNG does use a tiff structure at its foundation, that does not necessarily mean the data had been converted to RGB. DNG is certainly capable of storing non RGB data same as it is structured in a proprietary RAW format, maintaining the RAW file's ability to be adjusted for color balance, lightness, saturation. contrast,..

Again, I do not know much about how Vuescan creates the DNG file, so I am speaking in hypothetical terms. If the data Vuescan provides is similar to a digital camera's RAW file, then this is a significant advantage over a tiff file.

VueScan's RAW file seems to be a Linear RGB file- i.e. a RGB file with no curve or color space applied. Camera RAW files are often mosaiced bayer data. I am not sure a Scanner can even output mosaiced bayer data since it has a different CCD design than Digital Camera's but I could be wrong. In any case if you open a VueScan RAW file in a RAW processing program it has no problem adjusting it like a Camera RAW file.

[Rider]

The "raw" DNG file that Vuescan produces is the same as the TIFF file, data-wise. It's just a question of whether the software you are importing to prefers DNG or TIFF.

There is no advantage to either.

I found that although Lightroom supports both TIFF and DNG, there is no practical way to use the TIFFs because Lightroom does allow setting the gamma. Raw TIFFs imported into Lightroom look awful, whereas the same file as a DNG looks just fine straight away.

The other advantage of the DNGs is that it makes it easy for me to know what's a RAW file what isn't. If I scan RAW TIFFs and then convert some of them into output TIFFs, it would be a book-keeping nightmare for me.

[D. Bryant]

Vuescan doesn't produce a true RAW file compared to the data in a RAW file produce by digital cameras.

A scanner produces true RGB data, including Vuescan RAW data files. A digital RAW file containing a single channel grayscale unrendered data. A DNG file can contain rendered data but the data in a Vuescan DNG file isn't RAW data like that contained in a digital camera file.

A Vuescan RAW file was never intended to be edited directly with image editing software like PS or LR, etc. Creating a DNG file with rendered data is really muddying the water, I have yet to understand Hamrick's rational for doing that. DNG is just a variant of a TIFF file.

When processing a TIFF or Vuesan DNG file or any RAW camera file in ACR, LR, or other RAW processing software the file is edited in linear editing space (exactly why a Vuescan file edited directly in PS appears totally whacked out.)

A Vuescan DNG file is really a broken idea with no practical value, IOW a gimmick.

[Rider]

At a minimum, it lets me manage my files in a DAM program like Lightroom, something you can't do effectively with a linear RAW TIFF.

Also, my understanding is that DNG was never meant to be limited to digital camera files. The specification allows for both. I have no problem outputting great images from the DNG files using LR and ACR.

The only fly in the ointment is that Lightroom doesn't know what to do with the fourth channel of the DNG, the one that contains the IR data. But this is a failing of Adobe; they are often behind the curve on stuff like this.

Another problem is that LR probably doesn't support IT8 targets.

[D. Bryant]

At a minimum, it lets me manage my files in a DAM program like Lightroom, something you can't do effectively with a linear RAW TIFF.

Also, my understanding is that DNG was never meant to be limited to digital camera files. The specification allows for both. I have no problem outputting great images from the DNG files using LR and ACR.

The only fly in the ointment is that Lightroom doesn't know what to do with the fourth channel of the DNG, the one that contains the IR data. But this is a failing of Adobe; they are often behind the curve on stuff like this.

No it's not Adobe's problem and never will be. The data in the Vuescan DNG file has already been rendered, you might as well output in TIFF which can BTW, contain metadata. As I said before the RAW Vuescan file was intended to be used by Vuescan not other image editing programs.

And LR isn't supposed to support IT8 targets nor does ACR. You are demostrating my point about the VS DNG being an aberrant bastardized file format.

Strictly speaking DNG files were invented to address issues related to the digital camera RAW file tower of Babel, not the rendered output of from a scanner. Vuescan simply stuffs rendered data into a DNG container which in itself has it's DNA from the TIFF format. In short it's a hack.

If you like it great, but VS DNG ain't the same since it contains scene referenced data which digital camera RAW files do not.