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Archive 2013 · Official: Sony A7 and A7R Fullframe Mirrorless
  
 
AhamB
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p.148 #1 · p.148 #1 · Official: Sony A7 and A7R Fullframe Mirrorless


akuba wrote:
The encoding algorithm used for the Sony a7/a7R RAWs takes the original 14 bit values and maps them to 11 bit space [...]

The Sony RAWs are instead mapped on a curve and devote more of the 11 bit space to the portions of the exposure range that should benefit from more tonality. I believe this is why Sony considers it "visually lossless".


Is this in any way comparable to what Leica did in the M8? I've read that that camera maps 16 bit (or maybe it was 12?) values to 8 bit, with a curve as well.



Dec 28, 2013 at 08:46 PM
Samuli Vahonen
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p.148 #2 · p.148 #2 · Official: Sony A7 and A7R Fullframe Mirrorless


douglasf13 wrote:

It may have something to do with the amount of light available. With my NEX cameras, the cameras metered and focused at shooting aperture until you got into low light, where it switched over to focusing wide open.

This happens only f/5.0 and f/5.6, not on any other aperture with FE55. I would understand if it would not go below f/5.6 for example but I see no logical reason to have this only these two apertures.

For clarification exact explanation what happens (and NO this is no issue, just weird):
1. select aperture mode and aperture f/4
2. turn camera so you can see aperture
3. change to f/4.5 and physical aperture changes
4. change to f/5.0 and physical aperture changes
5. change to f/5.6 and there is no change in physical aperture
6. half press shutter, and physical aperture closes from f/5.0 to f/5.6
7. change to f/6.3 and physical aperture changes
(you can continue to f/22 and aperture changes in every 1/3 EV step)

And other way around:
1. select aperture mode and aperture f/6.3
2. turn camera so you can see aperture
3. change to f/5.6 and physical aperture changes
4. change to f/5.0 and there is no change in physical aperture
5. half press shutter, and physical aperture closes from f/5.6 to f/5.0
6. change to f/4.5 and physical aperture changes
(you can continue to f/1.8 and aperture changes in every 1/3 EV step)

I can't figure out any logical reason why this happens. However this will have no effect to practical photography.

Samuli



Dec 28, 2013 at 08:58 PM
snapsy
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p.148 #3 · p.148 #3 · Official: Sony A7 and A7R Fullframe Mirrorless


Samuli Vahonen wrote:
This happens only f/5.0 and f/5.6, not on any other aperture with FE55. I would understand if it would not go below f/5.6 for example but I see no logical reason to have this only these two apertures.

For clarification exact explanation what happens (and NO this is no issue, just weird):
1. select aperture mode and aperture f/4
2. turn camera so you can see aperture
3. change to f/4.5 and physical aperture changes
4. change to f/5.0 and physical aperture changes
5. change to f/5.6 and there is no change in physical aperture
6. half press shutter, and physical aperture closes from f/5.0 to
...Show more

I just tried mine again in normal and very low light and didn't see any behavioral difference between the two lighting conditions. However this time I did notice that one f/stop transition does not stop down in LV - for me it's f/5.6 -> f/6.3



Dec 28, 2013 at 09:12 PM
Taylor Sherman
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p.148 #4 · p.148 #4 · Official: Sony A7 and A7R Fullframe Mirrorless


Thanks for the details Akuba! Very interesting. It may be that any artifacts of this compression will be nearly invisible, however - perhaps ironically, by not giving users the ability to turn it off, Sony has forever left that uncertainty hanging over it. If you could compare uncompressed and compressed results, then people could see for themselves and then decide if they wanted to use it.

I wonder if they didn't have the processing power to do a more traditional, lossless compression on the RAW files. The space savings going from 14bpp to 8bpp is fairly substantial, but of course with a lossless compression, many images would have only been about 50% of the max possible size anyway.

Another thing about the A7 that I'm noticing - it was probably true of N7 but I didn't use high ISO much on that camera. Anyway - if you shoot at RAW+JPG, when reviewing in-camera it shows you the JPG. For high-ISO images, this can be pretty ugly. Switching to just RAW makes the review slower, but looks a lot better in that case.



Dec 28, 2013 at 09:21 PM
Toothwalker
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p.148 #5 · p.148 #5 · Official: Sony A7 and A7R Fullframe Mirrorless


akuba wrote:
The statement that 11 bits cannot support a dynamic range of 14 is not strictly correct, as your edit seems to acknowledge. Any bit-depth can express any dynamic range. A greater bit-depth simply allows for more granularity in the levels recorded within a given dynamic range. Whether 11 bits does justice to the dynamic range is a qualitative judgment.

There is nothing unclear about the bit depth of the Sony RAWs. The encoding algorithm used for the Sony a7/a7R RAWs takes the original 14 bit values and maps them to 11 bit space (a bit more on this below) and then
...Show more

Thanks for the good explanation. We agree then that the mapping is not lossless.

In my opinion, raw files should be as raw as possible.



Dec 28, 2013 at 10:13 PM
jcolwell
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p.148 #6 · p.148 #6 · Official: Sony A7 and A7R Fullframe Mirrorless


Toothwalker wrote:
...In my opinion, raw files should be as raw as possible.


+1



Dec 28, 2013 at 10:15 PM
philip_pj
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p.148 #7 · p.148 #7 · Official: Sony A7 and A7R Fullframe Mirrorless


I could so easily be wrong and it matters little, Taylor, but I always thought all images shown in Sony cameras were jpeg - whether the preview, histo display, review...all I had thought were sourced from in-camera jpegs, either tailor made (sorry) from image format setting choices to shoot jpeg or raw+jpeg, or from the small embedded jpeg created along with raw images. What settings would a camera show for a raw file review? Others will elucidate.


Dec 28, 2013 at 10:18 PM
Jonas B
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p.148 #8 · p.148 #8 · Official: Sony A7 and A7R Fullframe Mirrorless


elucidate...
I think you are right Philip. Just imagine, a histogram like today in the viewfinder but based on raw data instead of on the white balanced and calculated JPG and a raw based zebra function! For reviewing I think I prefer a JPG rendition (colours please) as long as it is big enough to check focus and DOF and optical artifacts critically. Well, we can dream on.
I also would like a proper shutter release with a half press trigger point...



Dec 28, 2013 at 10:26 PM
itai195
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p.148 #9 · p.148 #9 · Official: Sony A7 and A7R Fullframe Mirrorless


Taylor Sherman wrote:
I wonder if they didn't have the processing power to do a more traditional, lossless compression on the RAW files. The space savings going from 14bpp to 8bpp is fairly substantial, but of course with a lossless compression, many images would have only been about 50% of the max possible size anyway.


Perhaps they managed to hit their aggressive price point partly by skimping a little on image processing. I've also noticed the files fall apart faster than I'm used to from my D800 when lifting shadows. Maybe even faster than my X-E1. This is the kind of foible one might expect from a first generation product, though.

I've also noticed the terrible high ISO previews when shooting raw+jpeg.



Dec 28, 2013 at 10:27 PM
carstenw
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p.148 #10 · p.148 #10 · Official: Sony A7 and A7R Fullframe Mirrorless


jcolwell wrote:
+1


+2

Sony, for my birthday, I wish for a true lossless compression, no bit-reduction tricks please. I will gladly deal with file size and potential speed sacrifices.



Dec 28, 2013 at 11:12 PM
 

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carstenw
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p.148 #11 · p.148 #11 · Official: Sony A7 and A7R Fullframe Mirrorless


AhamB wrote:
Looks like they just got the width and height of the image reversed. It should probably look like this: http://i.imgur.com/fTuC2Ii.jpg


They also forgot the adapter. There is a spot in the lens setup for the adapter, but there are no choices in it.



Dec 28, 2013 at 11:14 PM
Gary Clennan
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p.148 #12 · p.148 #12 · Official: Sony A7 and A7R Fullframe Mirrorless


AhamB wrote:
Looks like they just got the width and height of the image reversed. It should probably look like this: http://i.imgur.com/fTuC2Ii.jpg


That is massive!



Dec 28, 2013 at 11:22 PM
James Burden
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p.148 #13 · p.148 #13 · Official: Sony A7 and A7R Fullframe Mirrorless


Any macro shooters here? What's the recommended lenses currently. I have a ton of F mount lens that may be going away but in the interim I did get a metabones NEX-Nikon F/G adapter. I have a humungous Sigma 150/2.8 OS that would be incredibly large on the A7......is there a good, old ai/s manual focus lens by Nikon that's a macro?


Dec 29, 2013 at 12:15 AM
Makten
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p.148 #14 · p.148 #14 · Official: Sony A7 and A7R Fullframe Mirrorless


James Burden wrote:
is there a good, old ai/s manual focus lens by Nikon that's a macro?


The Micro-Nikkor 105/2.8 AI-S is very nice, but has ugly bokeh when used at a bit of distance. I think it only goes to 1:2 also.

Edit: And if you're willing to use a shorter focal length, the 55/3.5 and 55/2.8 are really good and dirt cheap.



Dec 29, 2013 at 12:18 AM
James Burden
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p.148 #15 · p.148 #15 · Official: Sony A7 and A7R Fullframe Mirrorless


I'd rather go longer than shorter. If I had to go 1:2 I'd get another 100 MP...



Dec 29, 2013 at 12:28 AM
Makten
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p.148 #16 · p.148 #16 · Official: Sony A7 and A7R Fullframe Mirrorless


James Burden wrote:
I'd rather go longer than shorter. If I had to go 1:2 I'd get another 100 MP...


Then you are probably limited to AF lenses. Most MF macro lenses only go to 1:2 without a tube (which is sometimes included).



Dec 29, 2013 at 12:32 AM
Taylor Sherman
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p.148 #17 · p.148 #17 · Official: Sony A7 and A7R Fullframe Mirrorless


philip_pj wrote:
I could so easily be wrong and it matters little, Taylor, but I always thought all images shown in Sony cameras were jpeg - whether the preview, histo display, review...all I had thought were sourced from in-camera jpegs, either tailor made (sorry) from image format setting choices to shoot jpeg or raw+jpeg, or from the small embedded jpeg created along with raw images. What settings would a camera show for a raw file review? Others will elucidate.


I see what you're saying, but I definitely noticed a difference in the previews when I switched between RAW-only and RAW+JPG - same scene, same exposure, ISO6400. The latter showed more blotchiness, essentially what I'd expect from JPG compression of noisy data.




Dec 29, 2013 at 12:50 AM
carstenw
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p.148 #18 · p.148 #18 · Official: Sony A7 and A7R Fullframe Mirrorless


carstenw wrote:
They also forgot the adapter. There is a spot in the lens setup for the adapter, but there are no choices in it.


This is what it should look like. Excuse the rush job.

http://throughthelensdarkly.com/forums/NikonD800/CW_20131229_NikonD800_0002.jpg



Dec 29, 2013 at 12:57 AM
jhenderson0107
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p.148 #19 · p.148 #19 · Official: Sony A7 and A7R Fullframe Mirrorless


Toothwalker wrote:
Unclear. 11 bits cannot support the purported dynamic range of 14 EV.

Edit: A bit depth of 11 bits does no justice to a dynamic range of 14 EV. Or is it a matter of definition - again? If the dynamic range (the ratio of the largest non-saturating input signal to the smallest detectable input signal) is 14 EV, I would use at least 14 bits to store the information.

All analog to digital converters are imperfect. The ENOB (effective number of bits) of state-of-the-art 14-bit converters sampling at ~180 MHz (as within in the A7R ) is very close to 11 bits, so there is little justification to encode more that 11-bits into the compressed RAW image. The use of 11-bit samples within the signal processing chain in conjunction with the delta-encoding is well proportioned and fully justifiable, and is almost certainly visually-lossless in all but extreme corner cases.



Dec 29, 2013 at 01:54 AM
akuba
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p.148 #20 · p.148 #20 · Official: Sony A7 and A7R Fullframe Mirrorless


Taylor Sherman wrote:
I wonder if they didn't have the processing power to do a more traditional, lossless compression on the RAW files. The space savings going from 14bpp to 8bpp is fairly substantial, but of course with a lossless compression, many images would have only been about 50% of the max possible size anyway.


Regarding processing power: Venturing into speculation land, I suspect the driving constraint for Sony was either buffer space or data throughput. The algorithm they are using has the properties that it can be pipelined (it doesn't need all of the data to be staged in a buffer but can be applied as the data is streamed) and it produces compressed data with a fixed upper bound on its size (that being the 36M bytes). While many lossless algorithms can be pipelined, none of them can guarantee a fixed-sized upper bound on the output. In fact most can result in the compressed data being larger than the uncompressed data for worst-case inputs. Most implementations fall back to storing the uncompressed data in those cases but that requires either buffering all of the input data or reprocessing the bloated output back into the raw input for final storage. But at this point I'm digressing too far into computer science geekery so I'll leave it at that. I would assume Sony did a bunch of benchmarking with a representative set of images and concluded this algorithm met their design constraints whereas lossless ones did not.

jhenderson0107 wrote:
All analog to digital converters are imperfect. The ENOB (effective number of bits) of state-of-the-art 14-bit converters sampling at ~180 MHz (as within in the A7R ) is very close to 11 bits, so there is little justification to encode more that 11-bits into the compressed RAW image. The use of 11-bit samples within the signal processing chain in conjunction with the delta-encoding is well proportioned and fully justifiable, and is almost certainly visually-lossless in all but extreme corner cases.


The ENOB may be around 11.5 or so, so there may be some signal being lost as well, but I agree that the algorithm should be visually lossless for well-exposed images and that for everything but the deep shadows we're probably losing mostly noise. If I'm not mistaken, I recall mention that Sony may also be cooking deconvolution sharpening into the RAW, so the definition of what is raw may be changing anyway. But for peace of mind and for being able to push exposure in post-processing I personally would still prefer losslessy compressed data. Storage is cheap while paranoia is taxing. I think at this point most of us are fairly convinced that the encoding is good enough, but I'm not sure many of us would choose this encoding if there were a lossless option in the menu.



Dec 29, 2013 at 04:55 AM
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