The sRAW1 file close to doubled as a result of the conversion while the RAW file became marginally smaller. Is the smaller cr2 file size of sRAW1 or sRAW2 dwelt with in a different way to the cr2 RAW file by the dng converter resulting in a larger file ?
The RAW image contains a single pixel value for each pixel; this is 21 Mpix x 14bits, losslessly compressed.
The SRAW image is in a hybrid format; it is not truly raw any more. It is raw only in the sense, that the colors are in the camera's color space and WB has not been applied yet, but otherwise it has nothing common with the original raw format. It is demosaiced, i.e. the pixels have three color components. However, not each pixel has three separate color component: adjacent pixel pairs are sharing two of the three color components.
This format is Canon specific, DNG does not know such format. The nearest format in DNG is the "linear" image, which is demosaiced and each pixel has its own three color components. Thus the amount of data is much more in the DNG linear format than in the sRaw format. Of course, this does not represent any enhancement of the image quality, the DNG converter can not really add to the image content.
Pls convert one normal raw image of your 5D2 in linear format (click on Change Preferences, then double-click on Custom and select Linear demosaiced). You will see, that the result will be much-much larger (in fact about three times larger) than the original raw file was.
The question is if it is really useful in your situation to convert the 5D2 raw files. Valid reasons are:
1. you are working with PS CS3 (or even earlier version), thus your version of ACR does not support the 5D2 native raw files,
2. you want to avoid the XMP files with the adjustment parameters, and this is so important for you that you are rather multiplying the file size. If you are performing sophisticated adjustments and you want to save them as well, then you have to backup a 20some MB file instead of 5-10 KB of the XMP file.
Gabor
