They are not necessarily losing half of their resolution. But they are being compressed. In Bridge, are you converting to DNG using lossy compression? What sort of file size difference you see between your original raw files and DNG files in Lightroom?
What are you doing to the DNGs updating the previews or creating a new one using Save Image?
Check your preview embedding settings in ACR.
Thank you for your reply, Mr. Hess. The files are already DNGs because they come from a Leica M9 and a Leica M Monochrom which write their raw files in that format. I have been using the M9 and an earlier M8 for years. The DNG files they produce do not require conversion to work in Photoshop CS6 Camera Raw or Lightroom 4. Even files from a Panasonic Lumix GX7, which I convert uncompressed using the Adobe DNG Converter, are suddenly behaving the same way. I do not experience the problem when I run any of these files in Lightroom, where they retain their as-shot size. In Camera Raw, once they've been closed or saved as PSDs, TIFFs or JPEGs and sent to Photoshop, the DNGs shrink, and I cannot bring them back to their original (full) size. There's something to be said for backing everything up, which I always have done, but having constantly to retrieve back-ups is a tedious and nerve-wracking of working and does nothing for productivity.
I will greatly appreciate any guidance you can give me when you have the time.
For those of us without your camera(s), can you share an original-sized DNG that you save prior to using ACR, then share the size it is after working on it in ACR? These should be the same image at different stages in your workflow, but the content of the image, itself, doesn't have to be anything remarkable. Upload the pair of DNGs to www.dropbox.com or similar and post a public share link to them.
Thank you for your reply. I reluctantly attempted join dropbox and to "upload the pair of DNGs" but it apparently did not like my e-mail address. I don't get this at all. I don't understand why, after years of trouble-free operation, I should suddenly be having these problems with PS CS6 Camera Raw and Bridge. And why I am not permitted to speak directly to you or one of your co-helpers to address a problem that could probably be resolved in two minutes. Instead I'm obliged to deal with a file mailing system that fights me and have a tediously written conversation in tech language I do not grasp. Why does Adobe refuse to directly serve its customers? Would doing so nibble into its massive profits?
Sincere thanks for trying.
You are speaking directly to knowledgeable forum users via a keyboard and monitor with the benefit of being able to share and view example screenshots and share files. It's unlikely that someone in a call center in Mumbai will know what to tell you, so you're better off using these forums.
It would be useful to be able to see your files, but if dropbox.com is too difficult then we'll see about using screenshots directly in forum messages.
Starting over with your original assumption that the DNG files are losing half their resolution because they are half the size on disk, that is a false assumption. What's important is that the pixel dimensions of the raw data and the pixel values, themselves, remain the same. Other things in the DNG can be different and the essence of the image data is the same and you're losing nothing.
I mentioned that the filesize could be different if the embedded preview was smaller than what the camera put in the file. You can control the size of the embedded preview using this setting in the Camera Raw Preferences -- what is yours set to?
Jim mentioned Lossy Compression when creating a DNG from a RAW file. Since your camera produces DNGs, itself, this wouldn't be an issue, unless you were saving a new DNG from your existing one using the Save Image function in the ACR plug-in, which would not be the normal workflow, but you could be doing it, and haven't told us the precise details of what you're doing to know if this is a factor:
Thank you for your continuing effort on my behalf. First, I get it with resolution, which I mixed up with file size. The Leica M9 yields a DNG file of about 36MP uncompressed.
However, the user can opt to set the camera for about 18MP compressed instead. I go with the smaller file, which is large enough for my uses. But I do not want further compression and my files have never been further compressed until this incomprehensible trouble arose about two months ago. The attached screen shot is of a folder containing two nearly identical M9 photo files which were taken today. L1017645.DNG was sent into Photoshop CS6 Camera Raw via Bridge where adjustments were made to exposure, shadows, clarity and saturation. No changes were made to its dimensions. It began at 18.3MB and shrank to 12.2MB before I made a PSD from it. The PSD is gargantuan, but they've always gotten pretty big, why I don't know. The sister file, L1017646.DNG, was viewed in Camera Raw but was left untouched and it retained its size.
Yes, I changed to size of the preview to Full Size. No effect. Also, sometimes I make adjustments quickly in ACR, but I have never used Save Image and see no reason to do it.
When I do the entire routine in Lightroom 4, the DNGs do not become mysteriously compressed. My habit generally has been to first look files over in Bridge/Camera Raw, cull them and then have Lightroom import the folder for processing, etc. This routine has served me well enough, managing all the while to keep my clients happy. I'd prefer not to have to change for no good reason, but I know I can do it all in Lightroom if necessary. If I had had smoother sailing with DropBox, you could be looking at actual files now, but I didn't and I'm suspicious of what privacy DropBox offers, if any. I have removed DropBox from my computer -- quite a process in itself. (I've always sent finished work to clients on cds or dvds, although sometimes for a preliminary viewing they ask me to put JPEGs in their own DropBox.)
If you can get me back to where I was, I would be greatly obliged.
ACR will update the embedded preview of a DNG automatically. LR will only do it if you manually choose Update DNG Previews & Metadata from the LR menus. Perhaps LR 4 doesn't have this capability so you've never seen it occur.
Until you can share your files further analysis isn't possible. What makes Dropbox.com better than some sharing services is that once you delete the image, then show deleted images, and purge it from the online storage it is gone, even if the URL is still in a message, here. You can share images that have nothing personal, an out-of-focus picture of a wall, so even if someone found them, it wouldn't matter. I think you can use dropbox via the website without ever using the local client. OneDrive and GoogleDrive are alternatives.
I'm guessing the only difference in the Leica compressed DNGs that are 18MB and the ACR-updated-DNGs is the size of the embedded preview and perhaps a better compression algorithm the desktop computer is using vs what the tiny processor in the camera is capable of, although some Leica-specific metadata could be getting removed, things that ACR doesn't use. The only dangerous thing would be if the raw data in the DNG is getting lossy compression applied to it, which shouldn't be happening if you're not using Save Image and somehow overwriting your originals.
You probably have "convert to DNG" enabled somewhere, perhaps in Bridge or photodownloader, if you're using that. With default settings, that will result in the original Leica DNG being losslessly compressed. As its a lossless compression, it's not harmful, but if you don't want it, then change the bridge/photodownloader options.
O.K., I'll try installing DropBox again and attempt to send you the files. Will you PLEASE tell me EXACTLY how to use DropBox to get the files to you, including how to address them? And in the event that I am able to do that, please remember also that until two months ago I NEVER HAD PROBLEMS WITH FILES SHRINKING WHEN USING BRIDGE/CAMERA RAW. In fact, I never had problems with Bridge/Camera Raw at all and I used it regularly for years.
Thank you for whatever patience you have left.
I don't think you even need to install the client software, just use the website:
Open a web browser, IE, Chrome, FireFox, etc.
Go to https://www.dropbox.com/
If you don't have a dropbox user, then Sign Up and login.
If you do have a dropbox user then Sign In
Once you're signed in, click the Upload button and upload the files. You can first click the New Folder button next to it, and create a folder to put the files in.
After the two DNG files are uploaded, right-click on either each file or the folder you put them in and click the Share option:
You will get a pop-up panel that has the link to the file or folder as a URL--like this:
Copy that link to the folder or two individual file links into a reply message, here, or send them to me via e-mail: steve at sprengels dot com You don't need to actually send the links using that Share panel, just copy the link from the top box.
Assuming the photos aren't of a personal nature, sharing them with everyone on the forum will allow more participants to look at them if they want, rather than just myself.
Once you are ready to remove the files from dropbox, right-click on it/them and click the Delete option further down under Share. That will hide if from you, but won't permanently delete it, in case you made a mistake and deleted the wrong thing. To permanently delete it, click the little trash-can up along the top near the Upload button and the icon will change to have the trashcan lid open, which will unhide the deleted files as dimmer names than the non-deleted files. Right-click on one of those deleted files or folders and you'll be allowed to delete it permanently or restore it if you made a mistake.
Well, Steve, I'm not sure, but I think I sent you the link to a folder with my files. I don't expect you to puzzle over the contents now, but please let me know if you got them.
I meant to enclose this just in case, what I assume is the relevant link: https://www.dropbox.com/sh/k69e2te5yqtwe35/AAClJ6cgestouJ0jBSv_-dW8a?dl=0
Begin forwarded message:
From: Peter Kiar <firstname.lastname@example.org>
Date: August 25, 2015 6:13:13 PM CDT
Subject: Re: Why are DNG files processed in ACR losing half their resolution?
Well, Steve, I'm not sure, but I think I sent you the link to a folder with my files. I don't expect you to puzzle over the contents now, but please let me know if you got them.
Looked at the smaller file. Lossless compression, as I'd suggested above, almost certainly on import.
Thank you, Sandy, but why has it never happened before and how do I get it to stop happening now? I can't find a setting in Bridge or Photoshop Camera Raw related to it.
Checking right-click File Info in Bridge for the smaller DNG has LossyCompression = false so that's not the issue.
The only odd thing I see so far is that the DNG edited in ACR is being edited with ACR 8.2 instead of the current version of ACR 9.1.1. It's DNG Compatibility is a little bit different as well. Is there a reason you're still using ACR 8.2? Are you on a very old OS like 10.6.8?
Here is what happens when I edit the virgin file downloaded from dropbox in my ACR 9.1, as well as what happens when I save a copy using Lossy Compression:
Looking at the other DNG that is 11 MB and unexpectedly smaller after your editing in ACR 8.2 I'd ask what all has happened to it since it was first opened. There are several history steps listed, not just a single edit in ACR, two of which say Saved in New Location rather than Metadata Saved which to me means the DNG was recreated in a new location with whatever Save Image parameters in effect.
So "a very old OS like 10.6.8" has suddenly decided to sabotage me? Yes, I cling to a very old OS like 10.6.8 because I was perfectly happy with what I was getting from it and PS CS6 until now. That and my very old but still excellent film scanner cannot be updated for systems later than 10.6.8. No, I am not still shooting film, but I happen to have a career's worth of it, and every once in a while a past client will ask for something. "Then send it to a service," you will say. In order to avoid re-makes, I prefer to do my own scans.
As far as the DNGs that went to you, after they were shot the Lexar card they were on was inserted into a Lexar reader and when the relevant files showed up on my desktop they were put in a folder called "compression." From there, they were viewed in Bridge. The one that wound up being worked on was double-clicked in Bridge which brought up Photoshop Camera Raw, where I made changes to it. I believe I closed it and then re-opened it to check the settings I had made. It stayed with Bridge and Camera Raw. I expected it to have changed in size and confirmed it by clicking on the desktop folder and looking at the list within. The only other move I made was to put the files into DropBox for you.
When I took delivery of a Leica M Monochrome in early June, a program called Nik Silver Efex Pro was part of the package. I downloaded it from the internet and installed it on this no longer current Mac Pro, the one running the very old 10.6.8. (Maybe I should open a museum, huh?) Later, after these problems came up, I removed Silver Efex from the computer, thinking it could be the culprit, but apparently it was not. I have not reinstalled it.
To restate, I never have to my knowledge compressed a DNG file on this computer, the only one I use for processing photo files.
I am sorry I cannot be more helpful to either you or myself.
Can you try the simple steps I did with that one DNG that hasn't yet been opened in ACR?
- Make a copy using Finder of some other non-Adobe system method.
- Open Bridge on the folder that contains this copy.
- Double-click on it to open it in ACR.
- Click Auto above the Basic toning sliders.
- Click Done to exit ACR.
- Check the filesize of the copy in Bridge.
- Right-click on it in Bridge, and choose File Info... then see what the XMP Media Management Properties have in the Advanced tab -- see my screenshot, above -- how many xmpMMHistory structs there are and if any say Saved to New Location like the two do in the one smaller DNG you uploaded.
As far as museum relics, the current Mac OS is 10.10 and the current PS version would be CS9 if they still had that naming scheme. In other words, CC, CC 2014 & CC 2015 have all come out since CS6, and even CS6 is updatable to ACR 9.1.1 so it's only your OS that is limiting it back to ACR 8.2. I have no idea of ACR 8.2 is what is acting strangely or if something else is.
A question before the other questions I asked, earlier: how to do the files end up on your desktop after you put the memory card in the reader? What process copies them to the desktop, Adobe Bridge or an OS utility or third-party downloader program or what? And had you viewed any of the photos on the memory card before copying them to the desktop? If so with what program or OS utility?
I remove the card from the camera. The computer is in Finder. I put the card into an attached card reader. An image of the card reader comes up on the desktop. I click on it and a list appears of the files the card contains. I select the files I want and move them with the mouse into the folder on the desktop I have made for that purpose. When I do this there may or may not be other programs running on the computer. Finder is where I am, so what should I care? No, I never attempt to look at images on the memory card unless it is in the camera.
I went through the seven steps you outlined for me in your previous e-mail. I used a new file that had been moved to a folder as described above. I selected the file in Bridge and double-clicked it to open in ACR. After doing the Auto change, the file size showing on the bottom bar read 16.09 MB. An untouched sister file read 17.49 MB on the Bridge bottom bar. Different numbers show when the folder is opened in Finder. Why it did not shrink more is probably something only you know. I should remind you that none of this happens when I'm using Lightroom 4. Here are some screen shots:
Why are DNG files processed in ACR losing half their resolution?
created by ssprengel in Adobe Camera Raw - View the full discussion
A question before the other questions I asked, earlier: how to do the files end up on your desktop after you put the memory card in the reader? What process copies them to the desktop, Adobe Bridge or an OS utility or third-party downloader program or what? And had you viewed any of the photos on the memory card before copying them to the desktop? so with what program or OS utility?
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I asked how the files were getting to your desktop because you can use Bridge to copy the files and if that was occurring then it might be doing something, already, as it was copying them. Since you're just using Finder to copy the files nothing should be changing in them during the copy step.
The general difference between LR and ACR is that:
LR stores the settings (the changes from your clicking Auto) in its database and only reads data from the DNG, so the size remains the same.
ACR, on the other hand, is probably configured on your system to store settings changes with the individual files rather than a central database, which means ACR adds information to each DNG every time you click Done and in doing so is rewriting all the data and something is occurring during this rewriting of the DNG that is making it smaller.
The possibilities I can think of for why it is smaller is that it is compressing the data, either losslessly (which would be ok), or compressing the data using lossy compression (which wouldn't be good) or creating a smaller preview compared to what was in the DNG, initially (which would be ok). The preview can be set to Medium or Full Size.
The mystery is why your files are reducing in size when the settings are saved in them via ACR 8.2 while mine are increasing very slightly when I save settings to them (by clicking Done) when using ACR 9.1.1.
I can't find ACR 8.2 to test with but Adobe has ACR 8.3 online which is the last version that works with 10.6.8, I believe, so you could replace yours with it and see if that changes anything, just to make sure there isn't a bug in 8.2 that's been fixed in 8.3, or is there some reason you haven't updated to at least ACR 8.3?
When I use ACR 8.3 on your virgin DNG, click Auto, click Done, the size increases very slightly just like with ACR 9.1.1 so on a PC, at least, there isn't a bug that makes the file smaller and if yours does it must be a setting or workflow difference:
I would suggest you download ACR 8.3 from Adobe, replace your 8.2 with it using the process described on the download page, and test Auto/Done, again, with an untouched DNG and see what happens.
Here is the ACR 8.3 download page: Adobe Camera Raw Help | Adobe Camera Raw 8.4 or later on Mac OS 10.6, Windows XP, and Vista
For reference, here are my settings in ACR accessed by Ctrl-K:
Of particular interest is I have NOT enabled updating of the DNG Preview. Try your settings this way and see if things are any different for you.
I sent this and it wasn't delivered. Does this address work?
Begin forwarded message:
From: Peter Kiar <email@example.com>
Date: August 28, 2015 11:51:24 AM CDT
Subject: Re: DNG images viewed in Bridge Content no longer show changes made to them in Camera Raw (CS6). How can I fix this?
Can this, from August 3 when you helped me get DNG images appearing in Bridge to show changes made to them -- as they ALWAYS had, have led to the unwanted compression that plagues me now? Of three options shown in the thumbnail quality dropdown list, only Always High Quality is checked. A fourth, separate option, Generate 100% Previews, is unchecked. (I try not to mess with things I do not understand.)
Further, do I have anything to fear from downloading ACR 8.3? I am told my apps are all up-to-date when I check PS Updates, even though my ACR version is 188.8.131.52. As far as I can tell, ACR 8.3 is there for the taking.
Thank you for your persistence.
I don't think the Thumbnails quality setting would matter, it is telling Bridge whether to read the preview from the file or compute a new one on the fly, not whether to store something in the file. I have mine set to always high-quality, but I also turned off the setting in LR to not update the preview for a test just to cut down on the number of things that might be affecting the file. You could modify thumbnail quality in Bridge as an experiment if you want. Do it on a folder of test images just to be safe.
Over a year ago, there would have been a point in time where Check for Updates would have updated to ACR 8.3 and even ACR 8.4, but since the current version of ACR is 9.something, already, I doubt the checks for updates actually works, anymore, since your OS is so old.
If you are nervous about updating the version of ACR from 8.2 to 8.3, before doing anything, move the existing CS6 Camera Raw.plugin file (which will be 8.2) somewhere like to your desktop, so you can put it back if things don't work. Looking at the release notes of ACR 8.3 I don't see any mention of a bug being fixed that would be causing what you're seeing in ACR 8.2, and looking at the ACR 8.4 release notes, I don't see any serious bugs mentioned that mean you can't update to ACR 8.3. It's been too long ago for me to remember if there was anything strange happening with either 8.2 or 8.3 that people were discussing on the forums but wasn't mentioned in the release notes. Of course most people probably don't have cameras that produce DNGs natively so won't have run into things you might.
Another thing to try, which would keep Bridge out of the process, would be to directly open a copy of the untouched raw file directly from PS using PS / Open (I think) or maybe in Finder you can say Open with Photoshop, somehow, either of which should open it in ACR where you can click Auto and Done (not Open) and then review if the size has changed, using Finder.
I attempted to follow your suggestion to move the ACR 8.2 plugin to the desktop so I could try replacing it with ACR 8.3. I could not find the plugin to move it. Its name shows when I open ACR through Bridge. Its info can be found in About Photoshop, but nothing is given about its location. It is not on the PS CS6 list of plugins in Applications (or for that matter, on the lists of CS5 or CS4 which are not used but still in my computer). When I search for it using Find, it does not comes up. Can you tell me where to find it so I can move it and replace it with ACR 8.3?
The symptoms suggest there is no Camera Raw.plugin in the folder, now.
What is in the File Formats folder? Can we see a screenshot?
You cannot put the downloaded DMG (disk image) file in there, you have to open the DMG file by double-clicking on it to "mount" it, then copy the .plugin file from there to the File Formats folder that formerly had the older Camera Raw.plugin file in it.
Sorry. I got it loaded correctly on the second try. (I do not do this stuff every day.) I think the ACR 8.3 helps, but it still compresses the file* and it still gives me a gargantuan file in Photoshop. See below. The first file is an untouched one.
Here, from three months ago, is the way it used to be. Please look at number K15P0403 below, both as a DNG and a psd. Same exact camera. Same exact procedure on my part.
I no longer dare look at files in Bridge/ACR for fear they will compress and I will have to replace them with unshrunken copies from my backup discs. My only recourse is to work exclusively in Lightroom now. This whole thing is very discouraging.
*A Leica Monochrom file goes from 36 MB to under 24 MB.
Your in-camera compression from 36MB to 18MB is throwing away data, in a way that adds about 0.1 stop of noise. For ISO 640 and below this is noticeable. For ISO 640 and above the compression noise is less than the ISO noise and is meaningless. If you're shooting less than ISO 640 then shooting uncompressed will be slightly better quality, while above that compressed won't be doing anything worse than the high-ISO noise already is. Here is a detailed description of what is happening see here: DNG Compression, Any Difference in Quality? - Page 2 - Leica M9 / M-E - Leica Forum
So you're already throwing away data with the DNG compression in camera. I'd guess that Adobe is merely decompressing and recompressing the data differently in a way that's better since you're on a PC or Mac not the tiny processor in the camera, but isn't actually losing any more data. The only way to confirm this would be for you to supply the same DNG before and after ACR has updated it so the image pixels can be compared precisely to see if anything is being changed by the Adobe compression or not. Since you've already sent an untouched-by-Adobe version of L1017646.DNG how about sending a version of it after you've opened it and clicked Auto, then Done, in ACR and post that to Dropbox.com. You can do it with a copy so you can restore back the uncompressed version. I think it would be helpful to know if Adobe is just doing a better job of compression than your camera or if the data is actually changing. If the former then you have nothing to worry about.
Regarding DNG vs PSD size: a DNG is one-color-per-pixel, and in your case 8-bits per pixel, a PSD is 3-colors-per-pixel and 16-bits (hopefully) so 6 times more data, meaning an 18.3MB DNG would grow to 109.8MB as a PSD. The way to help this is to specify LZW compression when saving as I think that can still be read by Lightroom. The amount of savings would depend on how detailed or plain the image data is.
I'd guess that Adobe is merely decompressing and recompressing the data differently in a way that's better since you're on a PC or Mac not the tiny processor in the camera, but isn't actually losing any more data. The only way to confirm this would be for you to supply the same DNG before and after ACR has updated it so the image pixels can be compared precisely to see if anything is being changed by the Adobe compression or not.
As mentioned in a post above, the "Adobe compression" is lossless (emphasis on LOSSLESS) compression. What happens is that the 8-bit data produced by the camera is compressed (technically, Huffman encoding, if that makes any difference). The camera generated data isn't decompressed first. So what you get can be seen as "double compressed" - first by LUT based compression in camera, which takes each sample individually from 14 bits to 8 bit wide and is lossy, and then the 8-bit data is losslessly compressed by the Adobe software.
Note that this applies to the dng as posed here - with different settings at the compression stage you could get lossy compression, but that would require non-default settings.
This has gotten completely beyond me. I initiated what has turned out to be a tedious, unsatisfactory correspondence when I noticed the size of the DNGs I worked on in ACR via Bridge was suddenly diminishing. I had been using my M9 Leica for years, mainly processing the images in ACR and Photoshop. The DNG files had always stayed at the size they were when taken from the camera, 18.3 MB. In the last couple of months the DNG file sizes have been dropping to 9 MB or 12 MB or 17 MB when the files are modified in ACR. It never happened before. Some setting somewhere must have been changed, probably inadvertently by me, since I am the only person who uses this computer. I do not know what the setting might be or how I can restore things to the way they were. That is all I want: to restore what I had. I am very sorry you are incapable of helping me do that.
Why have we been obliged to use this nearly 19th century method of communication? I may as well be scrawling a message on paper, sticking it in an envelope and taking it to the post office.
The upshot of our answers is nothing bad is happening to your DNGs. They are being recompressed by Adobe products in a way that preserves the pixel information completely so despite this happening now when it didn't used to happen, it's fine. Ironically, having your camera set to Compressed DNG is throwing away some pixel information before the raw data even leaves the camera, but you seem ok with that.
If you want to pursue things further, as you say it's probably a setting, somewhere, that's different, now, that allows the DNGs to be touched by Adobe software and recompressed.
The two areas I can think of where a DNG gets touched by Adobe software during the use of Bridge and PS/ACR and would therefore have the possibility of being compressed are both controlled on the Camera Raw Preferences panel.
Please show us a screenshot of your Camera Raw Preferences panel.
You get to it by opening a raw file in ACR and either pressing Ctrl/Cmd-K or by clicking the three-dots-three-lines icon across the top. You can also get to it in PS, itself, using PS / Prefs / Camera Raw.
Here is what mine looks like for ACR 9.1.1, but ACR 8.3's should look very similar if not identical:
Here is a screenshot of my Camera Raw Preferences. They remained as they had been when Version 8.3 was substituted. The Default Image Settings had gone from nothing checked to what you see now in the hope it would help. No effect. I think the JPEG and TIFF Handling has probably always been as shown, but I do not know for sure. Other than sometimes following Martin Evening's (Adobe Photoshop CS6 for Photographers) and Jeff Schewe's (The Digital Negative) suggestions, I made it a point not to mess with things. Thank you again for your persistence.
Here are the two settings that I'm aware of that can touch a DNG file, thus causing it to be re-encrypted:
They are normally set the way you have set them.
The first one, about using XMP files, seems like it would need to be left that way, otherwise you'll lose your settings if you copy the DNGs to another location without copying the corresponding camera-raw database--something I doubt you'd do without specific instructions to do so. Have you ever changed computers and do your old DNGs, updated on the older computer, have their settings or not?
Updating the JPG Preview is optional so you could try it with that turned off.
Again, what is happening to your DNGs is not hurtful to them, and certainly not more that what you're already doing to them when you have your camera set to Compressed DNG.
Yes, I changed computers a few years ago and moved carefully to the once-new one I have now. RAW images from a decade ago have kept their settings, but I am not going to touch them in ACR. No way.
I just opened a fresh, 18.3 MB DNG, worked on it in ACR with JPG Preview off and it diminished in size to 16.6 MB. "No big deal," you may say, but understand that until May of this year, nothing I worked on in ACR ever changed size at all. Nothing. Ever. And yes, this one only dropped to 16.6, but a week ago some of them fell to 9 MB. Same camera. Same 18.3 original file size. How do I know that will not happen again? They can come out of ACR in different sizes, all smaller, and as far as I can tell, once they have, there is no way to get them back to original.
Is it ridiculous to want things as they were? I am talking about this May, not 1965.
Temporarily, try changing the two highlighted Camera Raw preferences to the indicated values of Store Settings In: Camera Raw Database and Update embedded JPEG previews to Off/Unchecked as shown below--the rest you can leave how you have them, click Ok, restart PS, then open a COPY of one of your untouched DNGs, click Auto, and Done, and see if it changes to be smaller or not.
If not then one of these two settings is responsible for your DNG recompression, when set to it's alternative state, and you can decide if you want to leave them that way.
The danger is leaving the top Settings Storage location set to Camera Raw Database is that the DNG files, themselves, don't have the settings, only a central database file that must be carefully moved from computer to computer for the settings to be carried over--perhaps this is what you did a few years back when you upgraded, moved the database across as part of the user settings. If you have it set to Use XMP... then the settings are embedded in each individual DNG and you won't lose them.
Storing settings in a central database file is what LR does, too, which is why the DNG files don't get modified, but it's more obvious what this Catalog/database file is called and where it is so it's easer to be careful to copy it across. The CR database is from ancient times with Adobe and it's never been obvious that is was in use or where it resides, even.
The reason the Adobe-compressed originally-18.3MB DNGs are sometimes 17MB and sometimes 9MB is that the amount of space savings due to the compression depends on how compressible the image data is. Areas of similar color, like majority sky, or very plain background is very compressible, especially at a low ISO, whereas highly detailed or high-ISO images aren't that easily compressed so will remain closer to the 18.3 original size.
It looks like you have gotten me back to where I wanted to be. Apparently the whole problem was caused by having Update embedded JPEG previews On. How or why I turned in on, I do not know. Now that it is off, file sizes stay as they were and changes made to images will show in Bridge after clicking on the thumbnail, as they always did. How a button called "Update embedded JPEG preview" relates to any of this I cannot understand, but it is Off and that is that.
Thank you once again for your continuing persistence. This has not been fun.
Update Embedded JPEG Preview being On is probably the Adobe-default setting and maybe you reset to defaults as part of some other fix back in May, or perhaps you inadvertently enabled that setting when you were in the Preferences area adjusting some other settings.
The camera puts an embedded preview in the DNG based on the camera’s processing of the raw data when the DNG is produced by the camera. This embedded JPG is what you see when you review a photo on the camera’s LCD or what LR shows when you’re doing an Import. The Embed Preview setting being On tells Adobe replace the camera-embedded preview with an Adobe-embedded preview that reflects the current Adobe settings.
The Adobe preview is a JPG that can change size depending on how compressible the content is so it is perfectly understandable that the filesize is different after the preview is updated. The only mystery to me is why the filesizes from the camera are all the same when the camera puts a Preview JPG in the file. There must be a bunch of wasted space that the camera reserves for larger embedded previews. It’s no wonder that Adobe rewriting the preview makes the file smaller.
Anyway at least you’ve figured out how to make things work similar to how they were before.