DNG File Size..

[nighthunter]

Talking to a photographer the other day,he runs a Canon Rebel XTI 10mp camera,his DNG file is 7.59mb.

I have a pentax 10mp camera and my DNG file weighs in at 16mb,both at 8 bits.

Any idea why the different sizes in file size?

Thanks.

[kevin_c]

Different compression ratio I expect.

My 20D (8.2Mp) files that I convert with Lightroom to DNG are averaging 7Mb, a fraction less than my '.CR2' RAW files.

[Mr. Pickles]

I think DNG compresses at a "constant" rate. If using the Adobe DNG converter tool, you can choose lossless or "whatever the opposite is.

Lossless is better, in that you don't lose stuff, but not sure the size difference between the two. You can change the size of the JPG preview built-in, but small in comparison, I'd think.

I'd think the reason you are "twice" as big is you have the original embedded and he doesn't, or you are not loseless.

I'd check and compare the "Change preferences" section.

Just to note, the DNG files sizes from image to image will go up and down, just like a JPG size does, based on the "colors" or "tones" in the image. The more you have, the bigger the file.

[kevin_c]

Just had a quick 'Google' and found this site:

DCRP Review: Pentax K10D

About halfway down the page they give 16.9Mb as Approx RAW file size. Maybe they are uncompressed?

[Tom Swaman]

I am no expert, but I have been reading and studying this fun stuff. First, the opposite of lossless, believe-it-or not is lossy.

Typically JPEG is a lossy format while DNG, and PSD and most RAW formats and TIFF are lossless file formats.

I believe that the answer to your question of varying file sizes is simply that the file results from how each camera computer and editor manipulates the information for storage. If you are using a RAW file, I believe these are lossless, but these are generated with different sets of rules, known as algorithms. An algorithm is nothing more than a mathematical formula or group of formula that create the pathways for data manipulation from one form to another.

I hope this is accurate and clarifies the issue of file size differences for different file types.

Tom

[kevin_c]

I don't think it's the type of file (and therefore the size) that is in question, it's the fact that a Pentax DNG file from a 10Mp DSLR is twice the size of a Canon DNG file from a 10Mp DSLR, even allowing for differnet image subject matter etc. - DNG is supposed to be a 'standard' file type across different platforms/cameras.

[kevin_c]

I've just converted one of my CR2 files to DNG uncompressed and it comes out at 16.6Mb, whereas an almost identical image using lossless compression is 6.7Mb

I assume the Pentax files are uncompressed. I Don't know if this can be changed in the cameras options?

[Mr. Pickles]

I don't really know why there is a DNG "lossy" option because I would think everybody wants "smaller", without a lose of data. If it was small and deleted stuff, then I see that.

[kevin_c]

Originally Posted by Mr. Pickles

I don't really know why there is a DNG "lossy" option because I would think everybody wants "smaller", without a lose of data. If it was small and deleted stuff, then I see that.

Who's saying this? I only get the option of 'Lossless' compression so I assume if I leave the box unchecked, no compression.

[Mr. Pickles]

Beats me. I thought some product I saw had a DNG compressed, with loss option. Made for even smaller files. I don't think it was the Adobe DNG version. I don't use the stand alone Adobe one anymore since I use Lightroom.

[kevin_c]

I've never seen a 'lossy' option myself. I have the same options in LR as I get in the stand-alone converter, although like you I use LR for my conversions (with lossless compression selected)

[Tom Swaman]

I am 99.44% certain that DNG is LOSSLESS!!!!! The purpose of DNG, as I understand things, is simply to create a standardized format for RAW images since Canon has different RAW formats, Pentax has different formats, Nikon has different formats, etc., etc., etc. Adope DNG Converter takes each of the individual proprietary formats and converts these to one uniform standard format designated "DNG".

[jfrancho]

Your choices for conversion to DNG are loseless compression, or no compression. Why you would choose to convert to DNG using only 8 bits/channel is beyond me. Tossing out data seems to fly in the face of archiving raw data in a universal format. Do not convert to 8 bits/channel until just before saving as a jpg.

[kevin_c]

Originally Posted by jfrancho

Your choices for conversion to DNG are loseless compression, or no compression. Why you would choose to convert to DNG using only 8 bits/channel is beyond me. Tossing out data seems to fly in the face of archiving raw data in a universal format. Do not convert to 8 bits/channel until just before saving as a jpg.

I didn't know you could convert to 8bit DNG (I believe they are 12 bit?)

[riha]

I think thay are whatever the original input are.

So if you convert an 12bit image then it will be 12 bit, but if you convert the new 1D mkIII files which are 14bit, then the dng ill be 14 bit. Can anyone confirm this?

[jfrancho]

The camera may capture 10-14 bpc, but the data is stored as 16 bpc, and your choices are 8 or 16 bpc when converting.

[Tom Swaman]

Today's electronics, I believe vary between 8 bit, 10 bit, 12 bit, 14 bit, 16 bit, 24 bit and 32 bit. I do know of equipment that uses each of these information depths.

I may be incorrect, but I believe that DNG is a file format that can store RAW data at 16 bit or below. I do not know whether DNG can store depths greater than 16 bit. DNG was established to support the full version of Photoshop which does process 16 bit RAW files. I believe that Elements processes 8 bit files, but can handle 16 bit information without losing this.

I know that I shoot 12 bit RAW as NEF files(Nikon D80), but I usually edit in 8 bit mode because of my eyes and my lack of ability to discern subtle color differences.

Now how is this for a bit of trivia and a few tidbits of not so colorful, possibly accurate information??