# Is it worth converting (scanned to) tif photos to DNG to save some space?



## NJHeart2Heart (Jun 25, 2015)

Title pretty much says it all.  For those who have done conversions from scan to TIF to DNG, I'd like to hear your experiences.  I've read about DNG for many years, but never considered until doing just one to experiment and seeing how much smaller the file footprint becomes... Does it hurt quality?  I'm just nervous about pulling the trigger on doing anything DNG...

Thanks!


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## clee01l (Jun 25, 2015)

Are your TIFFs compressed already?  DNG is really a subset of the TIFF/EP6 file specification.  So, in a sense, it is already TIFF.  Both TIFF and DNG Compression is lossless meaning you get every pixel out that went in to the compression.  However, it should be noted that in converting to DNG, there is an option to use Lossey Compression. While this will result in much smaller files You don't really want to do this with your only master copy. Lossey compression means that you get *don't* every pixel out that went in to the compression.  This is detrimental  and data loss (while always occurring with lossy compression) can become visually apparent with the 3rd or 4th generation JPEG derivative.


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## NJHeart2Heart (Jun 25, 2015)

Hi Clee,
Thanks for responding.  I didn't know that DNG was related to TIFF.  However, I can't tell you whether my existing TIFF files are already compressed, except for the evidence that when I converted one photo from TIFF to DNG (NOT LOSSY- I know about that and do NOT want to do that for all the reasons you stated above!), the file size decreased substantially.  These photos were scanned with an older Epson several years ago, if that helps give context...


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## clee01l (Jun 25, 2015)

Try this:

Use the Export function to Export one of your uncorked scanned TIFFs  In the Export file settings  Choose the file type as TIFF, Compression equals ZIP, Bit Depth equal 16. 
Repeat the Export. Choose the file type as TIFF, Compression equals NONE, Bit Depth equal 16. 
Repeat the Export. Choose the file type as TIFF, Compression equals NONE, Bit Depth equal 8. 
Repeat the Export. Choose the file type as TIFF, Compression equals ZIP, Bit Depth equal 8.
Repeat the Export. Choose the file type as DNG, Uncheck all three Checkboxes, JPEG Preview = Medium.  
Convert the Original TIFF to DNG, Uncheck all three Checkboxes, JPEG Preview = Medium.

Now compare the file sizes of the 6 images.  Is the Original TIFF 8 or 16 bit?  Compressed or uncompressed? How does it compare to the other TIFFS and to the DNGs Are Both DNGs the same size? (They should be)

Is there a significant savings gained by converting to DNG?


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## NJHeart2Heart (Jun 25, 2015)

Hi Clee,
That's a useful process.  I'll try that tonight to figure it out! 
To be clear, I read your reply to mean that by exporting in each option, and comparing the exported image file sizes to the original TIFF file size, I will know what type of file the original is?


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## clee01l (Jun 25, 2015)

NJHeart2Heart said:


> Hi Clee,
> That's a useful process.  I'll try that tonight to figure it out!
> To be clear, I read your reply to mean that by exporting in each option, and comparing the exported image file sizes to the original TIFF file size, I will know what type of file the original is?


Yes, Although there are other ways to determine 8 vs. 16 bit  and compressed vs uncompressed, this will give you the answer and possibly help you decide is the conversion is worth the time & Effort.  If they were my TIFFs, I would leave them if they are already compressed.  Convert and replace then with DNGs if they are not.


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## NJHeart2Heart (Jun 27, 2015)

Hi Clee,
Did that experiment just now.. 
The original file size of the test tiff is 262.1mb

TIFF, Compression equals ZIP, Bit Depth equal 16. --- 11.6mb
TIFF, Compression equals NONE, Bit Depth equal 16. --- 14mb
TIFF, Compression equals NONE, Bit Depth equal 8. --- 7mb
TIFF, Compression equals ZIP, Bit Depth equal 8. --- 3mb
DNG, Uncheck all three Checkboxes, JPEG Preview = Medium. --- 75.8mb  
Convert the Original TIFF to DNG, Uncheck all three Checkboxes, JPEG Preview = Medium --- 75.8 mb

So, it's interesting info.. but not sure what to make of it, other than DNG vs. orig TIFF size is quite significant...


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## clee01l (Jun 27, 2015)

NJHeart2Heart said:


> Hi Clee,
> Did that experiment just now..
> The original file size of the test tiff is 262.1mb
> 
> ...


This test suggests that the original TIFF is Uncompressed.  However, "TIFF, Compression equals NONE, Bit Depth equal 16. --- 14mb"  should yield a size similar to 262.1mb and It does not.  So I am suspicious of the Uncompressed 16bit TIFF values. If all of the rest of the original TIFFs are in that 200MB size range, I would say that it would be prudent to convert them to DNG.


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## johnbeardy (Jun 27, 2015)

Not to save space, but to avoid saving Photoshop edits destructively. For example, let's say in Photoshop I do something like resizing the picture or do some hamfisted edits. With the DNG method there's no chance I would overwrite the scan data.


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## Michael Naylor (Aug 19, 2017)

I'm fascinated by this, having scanned thousands of pictures.  I'm thinking that having them "wrapped" into DNG will make them safer when adding and changing metadata.   It will make them more robust.  However, I've discovered one major downside - MacOS doesn't understand this format and won't preview them in the Finder or with Preview.   LR, PS and Bridge will.


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## Hoggy (Aug 20, 2017)

A couple thoughts..
When doing the export tiff comparisons, make sure there is no crop selected.  Also make sure that any other resizing options aren't checked in the export dialog.

Another reason (the biggest for me) for converting to DNG is to add a checksum hash into the file, allowing for easy checking from within LR of file integrity.  This becomes even more valuable if one is writing the metadata to their files that support embedded metadata.

But do note that converted DNG's can't hold any layers at this time.  So if you ever use PS to make adjustments using layer techniques, you will have to save the derivatives as tiff/psd if you don't want the layers flattened.  This is also where John's technique comes into play.

Though I don't use Mac, so I have no idea about it's OS DNG support.


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