JPEG to DNG conversion size hit

[Jorge del Valle]

I've started converting some old JPEG images to DNG for consitency reasons. I'm using ACR to do this and it works well... mostly. The only thing is that I'm taking a huge size hit when I convert the files. I mean, I was expecting them to be bigger, but I'm talking about JPEG files of 3MB becoming 12MB files when converted to DNG. Is it really normal for them to become 4 times the size?

The thing that confuses me is that RAW images shot at about the same resolution are about 4MB in size when converted to DNG. Why then when I start from a JPEG image I end up with a 12MB DNG file? Am I doing something wrong?

By the way, these are the conversion options that I'm using (as recommened by Peter in the DAM book):
JPEG Preview: Full Size
Compressed (lossless): ON
Image Conversion Method: Preserve Raw Image
Embed Original Raw File: OFF

-Jorge

[danaltick]

Jorge,

Unfortunately, until the DNG spec. is revised, it stores a Tiff version of the Jpeg inside the DNG when converting JPEG's.  Hopefully Adobe will fix this in a later release of the spec.  The spec was not originally intended for JPEG's and I guess Adobe just hasn't gotten around to updating it for this.

Dan

[Jorge del Valle]

Thanks for the reply Dan. It all makes sense now.

As you say, hopefully this will get fixed in a later release. I just hope that I'll then be able to "reconvert" those DNGs that I've made from my JPEGs to the newer, leaner DNG version.

-Jorge

[danaltick]

I would hope so as well.  At a minimum though you could always get back the original jpeg if needed.

Dan

[Jorge del Valle]

I guess you mean by extracting the embedded JPEG? I haven't tested that yet. I'll give it a try tonight and compare the resulting JPEG with the original. If it's the same I suppose I can safely blow away the original JPEGs.

By the way, is there any information on when this new DNG implementation would be released (or even just on whether it's indeed in the works)? I've looked at the adobe forums but can't find anything.

[danaltick]

Jorge,

I believe a new spec is coming out soon, but don't know the exact date; however, I wouldn't hold my breath for the JPEG fix.  My guess is they're putiting most of the focus on the Raw data.

Dan

[peterkrogh]

Jorge,
While there will likely be some different compression schemes for source data in the DNG, I would not expect that the DNGs you've made from JPEGs to take advantage of this directly.  The data has been converted to TIFF data, so it *can't* store the original JPEG (which is the cleanest solution) unless you reconvert from the original JPEG.

I don't think this feature made the new DNG spec unfortunately (lots of other cool stuff did, but not this, I think).

Peter