Panasonic RW2 files Chroma Subsampling

[jarraun]

Hi IM5 users,

May be not important, just curiosity, I´d like to ask if any of your RAW files have the Chroma Subsampling tag: JPEG::SOF\YCbCrSubSampling\YCbCrSubSampling filled with some value. In my NEF files this tag is empty, which I think is correct, althogh RW2 files from Panasonic DMC-LX100 show a value of: YCbCr4:2:2 (2 1) in JPEG::SOF\YCbCrSubSampling\YCbCrSubSampling tag, I´d never expected that a RAW file will have chroma subsampling.

Thank you in advance for the feedback

Javier

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[monochrome]

No JPEG::SOF\YCbCrSubSampling\YCbCrSubSampling in my raw files. But since they come from a camera with a Bayer filter, I could argue that perhaps they should have it.

[jarraun]

Thanks monochrome,

Please could you be little more specific about why RAW files shold have Chroma Subsampling.

[loweskid]

Yes, mine show the same - Lumix DMC-GF2 - but nothing in NEF files.

[jarraun]

Thanks loweskid,

It seems it´s normal in Panasonic cameras, since I´m not an expert in chroma I don´t know if the subsampling could affect or not to the quality of the RAW image, let us hope that we are achieving the maximum of our Panasonic cameras.

[Ferdinand]

I know a little about chroma subsampling from a RAW converter I used to use.  If you converted a RAW to a JPG at very high levels of quality, you got insanely large JPGs, because there wasn't enough chroma sampling.  My understanding is that it's an aspect of JPG compression.  I doubt very much that it affects your RAW files.  It may relate to a matching JPG.  It may also relate to the embedded preview in the RAW, which is also a JPG.  I suspect that it's just a standard tag that Panasonic includes in all files.  The raw data in a RAW file should contain the light levels as measured at the sensor, undemosiaced and in linear gamma.

[jarraun]

Thank you Ferdinand,

I agree with you, must be a mere tag that doesn´t affect to the RAW image.

[monochrome]

Please could you be little more specific about why RAW files shold have Chroma Subsampling.

Sorry, missed the reply. Since the RAW files don't contain RGB samples for each pixel, but rather only samples a single primary at each pixel, I think it's reasonable to say that there's chroma subsampling. See: https://en.wikipedia.org/wiki/Bayer_filter

[cytochrome]

The RW2 from my GF1 have this tag too : YCbCr4:2:2 (2 1)

I came across a paper about sNEF : http://www.rawdigger.com/howtouse/nikon-small-raw-internals

It might shed some light. or more confusion?

Francis

[jarraun]

Monochrome, yes we could see the Bayer filter as some sort of chroma subsampling.
Francis, thank you but too complicated for me, no time here for theese very technic subtetlies