Archiving in TIFF or DNG as opposed to RAW(NEF)

[dmatsui]

Since coming to this forum i've been told shooting in raw over jpg is a must and i most certainly don't disagree. One point that confuses me that i just learnt is that allot of people on here convert their RAW files to either DNG or TIFF for archiving or even post processing. I'm mostly curious as to why, since i've started shooting in raw i've processed the files in raw and i store them on my hard drives in a raw format.
So why would people choose to convert their raw files before archiving? Or even post processing?

 

[Dwig]

...
So why would people choose to convert their raw files before archiving? Or even post processing?

To start with, you don't "convert RAW to DNG". It isn't possible because RAW is not a file format, its a class of image and DNG is a specific file format.

There are a number of classes of image data. The two that are important to photography are RAW and "RGB bitmap". RAW is a single channel bitmap where neighboring pixels represent different colors. RGB is a three channel bitmap where every image pixel is represented three times, once in each channel with each channel representing one of the three primary colors.

There are many RAW file formats. Most RAW formats are camera brand/model specific, like Nikon's NEF format. DNG is another RAW format that is brand/model neutral.

There are many RGB file formats. JPEG and TIFF are two common ones, though either can be three channel RGB or four channel CMYK. TIFF also supports "alpha" channels for masks and transparency effects.

The reason many converter their camera specific RAW images (NEF, ...) to DNG RAW images is that the DNG versioin is more likely to be supported by future software. Others prefer to "cook" their RAW files now and archive an RGB bitmap. They generally choose TIFF as the archive format since TIFF is a very common standard format that doesn't rely on a lossy compression scheme degrading quality. Also, TIFF supports high bit depth images (16 bits per pixel and higher), something JPEG doesn't.

 

[dmatsui]

ah that clears things up thanks

Others prefer to "cook" their RAW files now and archive an RGB bitmap

I'm curious as to what you mean by the term "cook"

I'm still slightly confused as to the differences between saving in for example TIFF, or DNG. Is it just personal preference?

 

[manaheim]

^^^ while I wouldn't disagree with anything Dwig said, I'm wondering if that isn't going to confuse the crap out of the OP.

Let me try to tone it down a bit...

Dwig is right... RAW is actually a class of images that are essentially digital negatives. We all here (and everywhere) talk about "RAW format" as a shorthanded way to say "the RAW format that your camera supports". For example, I shoot nikon, so my RAW images are actually .NEF format.

DNG is just a non-vendor standard for RAW images, so it's another RAW format with essentially all the same pros and cons.

NOTE: The following statement is my understanding, but I have never actually gone out and researched the statements to prove that I am correct...

Now... anything that ISN'T a RAW format (such as PNG, TIFF, etc.) are "digital negatives" in the way a RAW would be. The key with a RAW file is that you can adjust a significant amount of your exposure information before (as Dwig puts it) "cooking your image". This includes doing things like adjusting up to 2-4 stops of light one way or the other, etc. You cannot do this with a TIFF, PNG, etc. at the same level that you can do it with a RAW image. Once it has been converted to TIFF, PNG, etc. there is some information that just isn't in your cooked image. The benefit of TFF/PNG over JPEG/GIF is that the latter are lossy compression, so even more information is chucked when further adjustments on the image are made.

 

[manaheim]

And by "cook" he means "do a bunch of crap to the image and save it"... well, basically.

 

[dmatsui]

Right so basically from what i understand .DNG files are just another form of raw format, if i'm not mistaken its adobe raw format, anyway so basically the reason for saving your files as .DNG type files is more or less because these file types are becoming the standard raw file types and could potentially replace nikons .nef and canons, .cr2 (i think)

Looking at how you described the tiff format i would assume it would be advantegous to keep your files in the .nef or .dng format (as opposed to .tiff) by converting to tiff your essentially throwing away some information. Or at least this is my understanding.
based on what i've heard so far this would lead me to think that i should convert my images to .dng, is there any reason why i shoudlnt do this, or use another file format instead?

 

[manaheim]

Aside from the time and effort to make the conversion, there is no major reason why you shouldn't convert to DNG. That being said, the format hasn't been any more universally accepted than NEF or CR2 or whatever... so there's no assured way to know that you're backing the likely winner, and you may wind up having to convert them again in the future anyway.

My philosophy is that generally any major contender will always at least have a converter out there for it, so there's no reason to convert until you reach the point where you know your format of choice is really and truly dead.

 

[dmatsui]

That answers all of my questions, thanks allot guys.

 

[Joves]

Right so basically from what i understand .DNG files are just another form of raw format, if i'm not mistaken its adobe raw format, anyway so basically the reason for saving your files as .DNG type files is more or less because these file types are becoming the standard raw file types and could potentially replace nikons .nef and canons, .cr2 (i think)

Looking at how you described the tiff format i would assume it would be advantegous to keep your files in the .nef or .dng format (as opposed to .tiff) by converting to tiff your essentially throwing away some information. Or at least this is my understanding.
based on what i've heard so far this would lead me to think that i should convert my images to .dng, is there any reason why i shoudlnt do this, or use another file format instead?

Well you will lose some information from NEF to DNG but, it isnt all that great I have saved many NEFs as DNG. ANd frankly I have written Nikon about getting native DNG in camera. I dont like CaptureNX much, I use it but dont like it. I find CS to be much better to work with in my opinion. Nikon needs to do alot more work on the program. But having a unified RAW format would be nice for everyone, well excpet for the camera manufacturers with proprietary RAW formats.

 

[KmH]

........But having a unified RAW format would be nice for everyone, well excpet for the camera manufacturers with proprietary RAW formats.

Unfortunately, Adobe's DNG is also still proprietary though their converter is available free of charge.

Adobe is seeking ISO standardization. We shall see.

 

[Garbz]

The thing about RAW, TIFF, DNG for archiving, is it depends on what you do with your files. I edit once. Only once. I don't then waste hard disk space by storing files with information that can't be humanly perceived. So while I shoot in RAW and work in RAW / PSD 16bit until the job is done. But my final archiving is done in 8bit JPEG with the quality set to max.

This is personal preference of not storing information that is unperceivable, there there are people who I'm sure will re-edit their old files in which case archiving in this way is not an option.

Unfortunately, Adobe's DNG is also still proprietary though their converter is available free of charge.

Adobe is seeking ISO standardization. We shall see.

False the DNG is an open spec and the spec sheets can be freely downloaded from Adobe's website for anyone to implement their own decoder. And several manufacturers implement the spec too.