Adobe DNG Converter question

>  My question is: Does Adobe DNG Converter accept DNG files as input?

Yes:

• The GUI will allow you to use lossy compression.  On one sample file, I got ~90% compression with "Preserve Pixel Count."
• The command line version will allow lossless compression.  On the same sample, I got ~20% compression.  On MacOS:
  • "/Applications/Adobe DNG Converter.app/Contents/MacOS/Adobe DNG Converter" -losslessJXL -o outputfile.dng inputfile.dng
  • Documentation for the command line is at Adobe's DNG page under "DNG command-line interface specification".

(Note: I am not a Topaz user, but most of the reply below is about the Adobe side of things.)

One reason the Topaz files must be larger is that in order to process the files, the file cannot stay purely raw. The single stream of raw data must be demosaiced into three RGB channels. That by itself can triple the file size. In addition, if a camera captures 10 to 14 bits of data, photo apps only output 8, 16, or 32 bits per channel, so if your camera captures for example 14 bits, then the three RGB channels Topaz converts to may be at 16 bits per channel, and if that happens, that makes the file another level larger.

The same file size expansion happens when, for example, Lightroom Classic applies AI Denoise, because it must expand a raw file to a demosaiced DNG for the same reasons and with the same consequences.

If you’re using Lightroom Classic, then you do not necessarily have to use DNG Converter, because Lightroom Classic (and Camera Raw too) already has those DNG Converter features built in. (I think Topaz recommends DNG Converter as a free solution to account for the many people who are not using Lightroom Classic.) 

In Lightroom Classic, see if this works for you (try it out on test files first before doing it on irreplaceable images):

1. Select DNG files returned to Lightroom Classic from Topaz. 

2. Choose Library > Convert Photos to DNG. 

3. In the Convert to DNG dialog box, deselect “Only Convert Raw Files” so that it will process DNG files. 

4. Select “Use Lossy Compression”. This option should also be in DNG Converter, and I think you have to select that if you want the file size to go down. 

After you click OK, Lightroom Classic (like DNG Converter) will process the images. The big difference with, and the big benefit of, doing it in Lightroom Classic is that it already knows about these images, so it is able to replace them in the catalog without corrupting the catalog. It automatically relinks the database instances of the originals, including existing metadata, to the new DNG copies it made, and unlinks the originals (they no longer appear in the catalog). If you also select “Delete Originals After Successful Conversion, then the originals are deleted; if you don’t select that then they are left in the folder even though they are not visible in the catalog but that would defeat the purpose of saving storage space.

Lossy DNG compression should be almost visually identical to the original. It uses compression that is better than (so, not as degraded as) JPEG compression. However, if it was me, I would not apply lossy DNG compression to images I rate the highest or which must retain as much quality as possible because I want to make large prints or something. But there should be no visible quality loss for images that will only be printed small or posted to social media, for example; so I would have no problem applying lossy DNG compression to those.

> My question is: Does Adobe DNG Converter accept DNG files as input?

yes it does ... 

in the future, to find the best place to post your message, use the list here, https://community.adobe.com/

p.s. i don't think the adobe website, and forums in particular, are easy to navigate, so don't spend a lot of time searching that forum list. do your best and we'll move the post (like this one has already been moved) if it helps you get responses.

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