JPEG to DNG

[Dale]

The DAM book (p444) talks about whether to convert camera-original JPEG files to DNG.

Question 1
It says a reason to do so is that if you use LR or ACR to adjust JPEGs that LR, ACR and Bridge will show the adjustments but other programs will not. Apparently converting to DNG resolves this.

Can someone explain in more detail what LR or ACR does to a JPEG when it edits it? It seems like the end result is not a JPEG, for if if were a straight JPEG of the kind that would be created with pixel-level editing, another program would not have trouble viewing it. (It seems non-destructive ACR-type editing is applied, but since the file is not a DNG, where is this stored?) However, it is not a DNG, or there'd be no need to recommend converting it to a DNG. It's not clear to me exactly what the image is.

Question 2
Any progress on the possibility of a new DNG spec mentioned that might store the original JPEG image more efficiently?

Question 3
JPEGs at times seem to grow for reasons that are not entirely clear. Consider the following:

I start with an original JPEG #1 which is 2,331K.
I edit #1 to produce JPEG #2 which is 6,262K.
I edit #1 in ACR and save as DNG #3 which is 18,668K.
I edit DNG #3 in ACR as save as JPEG #4 which is 6,236K.

The only conclusion I can reach as to why the JPEG size has grown is that I have saved it in highest resolution, and less compression is applied. If that's the case, am I losing quality in the decompression?

Dale

[peterkrogh]

Dale,
I'd say it's probably best to wait, unless there is a compelling workflow siituation you face.

You might want to watch this movie:

http://www.dpbestflow.org/image-editing/parametric-image-editing#not

Peter

[Dale]

Peter, thanks for directing me to the summary.

I'd say it's probably best to wait, unless there is a compelling workflow siituation you face.

I take this to mean that for now you'd use DNG for RAW files, but not for legacy JPEGs.

Thinking through the process leaves me with a few thoughts and questions.

• When a legacy JPEG is edited, PIE instructions are in the xml data just like they are in DNG files.
• If I want to share a photo, send it out for printing, etc. I need a non-PIE big-adjusted JPEG.
• Therefore I need a PIE-version containing non-destructive edits, but also a non-PIE version.

Q, Wouldn't the naming convention have to distinguish between the PIE and the non-PIE versions, unless the PIE version is saved as a TIFF?

Q. Does a PIE JPEG contain an embedded preview as does a DNG? I'm guessing it does is why my JPEGs grow after ACR editing.

we’re moving closer to a world where you only need to have one copy of each source image, with all versions and variations saved as instruction sets…

Since each variation produced with PIEware is just a set of instructions, you can experiment with different image interpretations without filling your hard drive with duplicate files. You can save the variations you like as virtual copies and return to them later.

Q. I'm reading this to say that ACR allows for different editing instructions for different versions within a single PIE file, say one cropped and one not. Is that correct?


Dale

[peterkrogh]

Dale,
Did you watch the movie?

>Q, Wouldn't the naming convention have to distinguish between the PIE and the non-PIE versions, unless the PIE version is saved as a TIFF?

Perhaps in naming, or perhaps in file handling.  Since my archive is built around a single-original archive, no real reason to use two names.  If I make a file to send out, it's nearly impossible for me to get the two confused, due to the structure of the archive.

Q. Does a PIE JPEG contain an embedded preview as does a DNG? I'm guessing it does is why my JPEGs grow after ACR editing.
No, a JPEG has only one full res copy of the image, so the pixels are what the pixels are.  The difference in size would be due to the added instructions.
Peter

[Dale]

Peter,

Did you watch the movie?

When I followed the link earlier I didn't notice that Figure 5 was a movie so I wondered where the movie was. I went back and looked again and found it, and have now watched it. It was well done and helpful. Thanks for pointing me back to it again.

Since my archive is built around a single-original archive, no real reason to use two names.  If I make a file to send out, it's nearly impossible for me to get the two confused, due to the structure of the archive.

OK, I can see how that would be the case. I do like the structure you proposed and am in the process of implementing and migrating to a similar one.

Thanks for your thoughts.

Dale

[Dale]

According to p. 444,

...adjusting JPEGs can cause real confusion. Lightroom and Bridge will show the images with the corrections, but other programs will show the unadjusted images. Converting to DNG helps to clear up the confusion since it's designed for parametric image editing.

The way I'm reading that is this -- Other programs can't read the adjustments to the images whether those adjustments are in a JPEG or in a DNG. The difference is that ACR will create a JPEG preview in the DNG that other programs can read and display, while there even a PIE-ware edited JPEG has no such preview. Therefore, other programs can only display the original unadjusted images. That seems to be the only reason for converting JPEGs to DNGs, other than possibly consistency of workflow.

If that's the case, then it's very clear why you said it's best to wait.

Dale

[peterkrogh]

Dale,
Yes, you've pretty much got it.
The one other reason to make DNGs now is that you want to take advantage of the data validation function.
Peter