On Thu, Feb 07, 2013, John Francis wrote: > > The namber of bits of uncompressed RAW data are: > > K-x: 12MP x 12 bits/pixel = 18MB, > K-5: 16MP x 14 bits/pixel = 30MB. > > So on the K-x you're seeing about a 20% saving, while on the K-5 > you're effectively getting close to no compression at all.
That's very interesting because.... > If I look at the shots I took with that same body on the previous time > I used the camera I'm only seeing DNG sizes of around 20MB. I was > intrigued, so I looked a little closer. I think the single biggest > factor is that you're using higher ISO (1250 in the couple of shots I > looked at), while most of the time I'm shooting at 320 or lower. > > This suggests to me that by the time you crank the ISO up to 1250 > you're approaching the point where the low bit of that 14-bit pixel is > effectively noise, so lossless compression isn't helping you much. ...many of my shots on the K-x are higher ISO (4000-6400) because I've been shooting indoors. OTOH, now that I'm taking a closer look, the K-x files are varying between 10MB and 17MB, while the K-5 files are varying between 24MB and 29MB (albeit with less environmental variation). It's also not too surprising that the K-5 JPGs vary from 7.7MB to 13MB. The 7.7MB JPG has the 29MB DNG, I'm guessing because that one has such a large swathe of blown highlights. Actually, now that I look at the photos and the file sizes, it looks like the DNGs with more dark areas are smaller. Which makes sense if you think about it: light areas likely have noise in the short bits but dark areas won't have noise in the high bits, which is what drives the lossless compression. -- Hugs and backrubs -- I break Rule 6 http://rule6.info/ <*> <*> <*> Help a hearing-impaired person: http://rule6.info/hearing.html -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
