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The ratio between the size of an original raw image and a DNG file will depend on the original file and how aggressively it was compressed. You will notice the greatest difference when you have converted uncompressed raw images. But since your sRaw images were already compressed the DNG file will be larger because of the type of compression used in the initial writing of the DNG file.
Thanks for your explanation. I thought that might be the case, but wanted to make sure that what was happening was legit and not something I or the software did wrong in the capture or conversion.
The reason for the larger DNG file is quite complicated, one needs to know some JPEG details. In short, the original sRaw file contains four 15 bit pixel values for two pixels, while the DNG file contains three values per pixel.
The size difference would be much larger if the CR2 file did not contain a 050 KB large thumbnail, which is in the DNG file only between 100 KB abd 200 KB large (approximation).
Plus, the DNG converter fine-tunes the compression; this is not affordable in-camera.
I agree with G. Sch. about "four 15 bit pixel values for two pixels", for sRaw and sRaw2. For sRaw1, we have 6 values for 4 pixels.
more details here: