Lossy DNG File Sizes by ISO.

Fairly recently I discovered the magic of lossy DNG's. My stock photo library is ever growing. Though JPG's might really be enough for my archive, I've been keeping my raw files. RAW files take up lots of space. And RAW files can't typically keep user generated EXIF data in the file. RAW files keep their keywords and other metadata in a sidecar, that is if you regularly save the EXIF data to file.

So recently I've been converting all my RAW files to lossy DNG's.

After testing the highest ISO setting on the new-to-me A7R IV, I converted the files to lossy DNG's only to find a surprise. The very high ISO lossy DNG's were much larger than the original Sony RAW files!

Lossy ARW vs Lossy DNG full image sample

So I thought it would be a good test to shoot from the lowest to highest ISO, convert to lossy DNG and see where the file size savings invert. Here's the data as seen in the above screen shot:

ISO	Lossy Sony ARW Raw file size (MB)	Lossy DNG file size (MB)	efficiency
100	62	19.5	3.179487179
200	62	22.6	2.743362832
400	62	26.1	2.375478927
800	62	30.2	2.052980132
1600	from Lensbusters.com 62	35.7	1.736694678
3200	62	44.3	1.399548533
6400	62	54.6	1.135531136
12800	62	72.6	0.8539944904
25600	62.1	83.7	0.7419354839
51200	62.1	99.7	0.6228686058
102400	from Lensbusters.com 62.2	110	0.5654545455

At ISO 100, I saved 3x over the Sony ARW file. By 6400 file sizes were more or less even. At the highest ISO setting the lossy DNG took up roughly double the space of the original ARW file.

Lossy ARW vs Lossy DNG 100% image sample

This was just an exercise out of curiosity. For my, and I expect for most all of our workflows, the Lossy DNG offers a lot of savings in HD space. If you shoot lots of really high ISO shots, maybe it's not worth converting.

But for my library, lossy DNG's are great!

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