The sRaw format is not covered by the DNG specification. When converting, it must be changed; in fact, the amount of data needs to be increased by 50%.
The rest of the difference comes from preview(s). If you select "large preview", then a large AND a small one gets created. A thumbnail is always created.
Note, that the size of the sRaw1 CR2 too includes a preview, size over 1 MB, one small thumbnail, 11KB, and another small thumbnail, 500KB (this one is uncompressed). The raw data itself is 7-10MB.
Thank you. This doesn't offer a "solution" in terms of avoiding the larger file size (and defeating the purpose of choosing the sRaw1 format) but at least provides an explanation.
I too am suffering from the same issue as Alan however still a little stuck as to why my CR2 files from a 5D decrease in size when converted to DNG from for example 14.4MB to 11.8MB while the 5D mark II files increase from 8.7MB to a much larger 23.6MB after conversion. Both conversions are being done with DNG Converter 5.4 using the same preferences. Any light you could shine on this for me would be greatly appreciated.
still a little stuck as to why my CR2 files from a 5D decrease in size when converted to DNG from for example 14.4MB to 11.8MB while the 5D mark II files increase from 8.7MB to a much larger 23.6MB after conversion
You are talking about 5D RAW files vs. 5D2 SRAW files. If you record a 5D2 RAW image and convert that in DNG, then the size decreases.
Your question indicates, that you are not aware of the options offered by the 5D2. A 5D2 sRaw file is much smaller than a raw file (depending on which sRaw you selected), but the image too is much smaller: 10 Mpix or 5.2 Mpix vs. the full size, 21 Mpix. I wonder why you don't find it strange, that the "raw" files of the 5D2 are smaller than those of the 5D.
Thanks for your timely response and I apologize for not being more
specific with my question. I am aware that the 5D mark II has three
"Raw" file recording options RAW, sRAW1 & sRAW2 in fact that is why I
updated cameras as my work often only requires a maximum print size of
6"x9" for which sRAW2 at 5.2 Mpix will suffice.
My question relates to why 2 files both shot with the 5D markII in
different RAW shooting modes convert to DNG so differently ? For
example a say 17.7MB sRAW1 file after conversion to DNG becomes a 27.9
MB file while as you correctly stated a RAW file of 31.4MB converts to
a 25.1MB DNG. 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 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.