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Destructively crop RAW DNGs in LR?

H2oggre

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Is there someway to make my filesize smaller in images with wasted space? I have images with a small subject in blank background (e.g. fish centered in blue water or bird in blue sky). The DNG filesize does not get smaller with a crop. I can sort of decrease filesize by exporting as a DNG using save as "lossy DNG". But I've still got all that blue. Short of investing in longer glass, can't I reduce filesize in LR or PS just by cropping a subject and toss the background?
 

Roelof Moorlag

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Lightroom does not touch the file itself, it is non-destructive. You have to export the cropped file, then you can get smaller files also. What is it that you want to accomplish exactly?
 

H2oggre

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It just irks me to save a 12 MB DNG file when 2MB will do. My subject is surrounded by extraneous, not-ever-needed blue. I have been
  1. Developing in LR
  2. Cropping (nondestructively, I know, but I would rather throw away what I don't need).
  3. Exporting the DNG as a lossy DNG (but this saves the original dimensions as if it were never cropped)
This results (see jpgs of the DNGs - the forum won't let me post DNGs) only in a reduction from 12MB to 7MB and was lossy. I don't want to degrade my subject. Just toss the extraneous stuff.
note you cannot use file sizes on these jpgs. Its the DNGs I want to reduce in size. Its just that this forum does not allow DNGs.
 

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LRList001

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Is there someway to make my filesize smaller in images with wasted space? I have images with a small subject in blank background (e.g. fish centered in blue water or bird in blue sky). The DNG filesize does not get smaller with a crop. I can sort of decrease filesize by exporting as a DNG using save as "lossy DNG". But I've still got all that blue. Short of investing in longer glass, can't I reduce filesize in LR or PS just by cropping a subject and toss the background?
You need to decide why you want the DNG at all. If you are happy with your edit, what is wrong with the jpeg? Or, you could create a 16 bit TIFF (which will be big compared to the jpeg). You could even import the TIFF back into LR and export as a DNG, but as a DNG derived this way it won't work as a proper RAW file. If you do want the original DNG then you are stuck with it being the original size, that is one of the 'way things are' facts. As already commented, disk space is cheap. Given the DNG is roughly the same size as the TIFF, the DNG probably acts as a container for the TIFF.
 

Conrad Chavez

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It just irks me to save a 12 MB DNG file when 2MB will do. My subject is surrounded by extraneous, not-ever-needed blue.
The file might already be close to the smallest original quality file size you can get for that image. DNG and raw are both compressed formats , probably already smaller files than the cropped version would be in TIFF or Photoshop format. The only reason JPEG is smaller is that it's lossy. At this point, you don't have much to gain.

Also, the area you cropped out involves a narrow range of color and tone, without fine details. That's much easier to compress than a complex area of varied color, tone, and texture, so the area you want to crop probably isn't using that much storage space in the first place. So cropping it out is unlikely to free up much space if it could be saved as a DNG, and it very likely wouldn't reduce it all the way down to the 2MB target you mentioned.
 

clee01l

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It just irks me to save a 12 MB DNG file when 2MB will do. ....This results (see jpgs of the DNGs - the forum won't let me post DNGs) only in a reduction from 12MB to 7MB and was lossy.
. First, I don't think you understand what a RAW DNG file is. It is not an image (that's why you can't insert it as an image in the forum) It does not have pixels and is not even RGB. The data block consists of numerical values obtained from each photo site, Each Photosite has a red, or green or blue filter overlaying it. Each photo site is a 12 or 14 bit floating point number that when converted to RGB and combined with the adjacent photo sites can create a 16bit Red, Green or Blue value. It takes all three of these to determine the actual color at a given pixel When you demosiac and convert to RGB, you get a processed pixel at each photo site composite. You also have introduced tone adjustments, fixed the white balance, filtered for noise and sharpened the image. IOW, you have locked in these adjustments that you can't undo without returning to the RAW file and reprocessing.
The other thing that you have in the DNG is a fully processed JPEG thumbnail that the camera produced. This is the image that you see on the camera back screen or when you first open the image in LR.
When you crop an image in LR, you isolate a set of pixels that you want LR you show you from the full image. The only way to reduce the number of Pixels to those in the crop window is to export the image. You can export to a lossless compressed TIFF format but this exported image will always be fixed wrt the processing adjustment applied at conversion to RGB. If you screw this up or want a different result (like correct a blue color cast on your subject), you need to start over with the RAW file.
You are worried about the size of the RAW image file at 12 MB. You should consider the file sizes of full frame DSLRs and Medium format cameras. Mine average about 43MB.
If you have a keeper image, then you want to preserve the original (DNG stands for Digital Negative Graphics), just as you would preserve the original film negative. If you are resisting buying more storage, consider the images that did not make it and cull rigorously. Most of us have about 5% keepers and the other 95% should be trashed. Yet we are reluctant to discard that 95%. Once you have finished housekeeping on your images, then look at all of the document files stored in your documents folder.
 

Dan Marchant

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It is generally not a good idea (given how cheap storage is) to throw away the original RAW. Just because you don't need it now doesn't mean you wont at a later date. A friend might want a print but in a different aspect ratio. Or you might want to reprocess the image after learning a new technique or buying some new software.
 

H2oggre

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Thank you all. And especially Dan & Cletus. Your points of different aspect ratios needed later, and tighter housekeeping are good ones.
So Cletus, when I make changes to a large DNG in Lightroom, I'm looking at the "preview " stored. Are these jpgs like the original thumbnail or just a new re-"drawn" bunch of pixel from the red, green, and blue, photosites?
And I am aware storage prices are dropping, but like you say full frame and even "enhance details" results increase my future storage requirements. I just hate storing all the unnecessary parts of my image because I did not have enough [reach on the] lens or could not get close enough. What started this was I read that lossy DNG was not discernably different from regular DNG. Yet in my case results in 40% less filesize so I jumped on that.
But you are right - I should be spending my time being more brutal in my culling. I'm too close to my shots. I need a more brutal editing mentality, Thanks for your points.
 

clee01l

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So Cletus, when I make changes to a large DNG in Lightroom, I'm looking at the "preview " stored. Are these jpgs like the original thumbnail
Your camera always creates a fully processed JPEG. When you save the RAW image in the camera, this fully processed JPEG is available for review on the camera back and as a thumbnail stored in the header section of the RAW file.
All previews in LR are stored in the LR Previews folder. When you initially import a RAW file into LR, the thumbnail from the header section of the RAW file is copied to the previews folder. The RAW data is demosaic'd, converted to RGB (pixels) and preprocessed. When you first open the image in LR, LR will take this preprocessed RGB image and replace the existing thumbnail with this preprocessed RGB image.
 
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