CMOS/ADTG/Digic register investigation on ISO

[Audionut]

Yeah I'm pretty sure I'm just being pedantic, since resolution doesn't care about well depth.

Now I'm going to assume Canon's full-stop ISOs are pretty much correct, but I'll keep the relative differences measured by DxO between the two cameras. That difference is...

Code: [Select]

octave:1> isos_dxo_5d3        = [ 80    160    323    641    1280   2518   5179  ];
octave:2> isos_dxo_6d         = [ 80    153    311    616    1210   2400   4991  ];
octave:3> isos_dxo_5d3 ./ isos_dxo_6d
ans =
   1.0000   1.0458   1.0386   1.0406   1.0579   1.0492   1.0377
octave:4> log2(mean(isos_dxo_5d3 ./ isos_dxo_6d))
ans =  0.054522

=> 6D ISOs are 0.055 EV lower than 5D3's.

But only at gains higher then base?  Since the base gain is generating the same ISO on both cameras, this should mean that they capture the same amount of photons.  Or rather, that since the 6D has an higher rated well capacity, that it generates more electrons for the same number of photons.  Since ISO based on saturation, should be representing a fixed photon count, right?

edit:  Nevermind, I reread your post.

[Levas]

Don't know if this is correct, but the way I think about it is:

A full frame CMOS chip has han area of 36mmx24mm= 864mm2 to catch light.
Since CMOS has circuitry inside the chip, this circuitry is blocking light (that's why backside illuminated CMOS sensors are slightly better in catching light, backside illumination prevents the circuitry from blocking light).
By normal CMOS, the pixel wells are below the circuitry.
So due to circuitry the active area of CMOS full-frame is a little lower then 864mm2

Now my assumption is, that the 5d3 CMOS chip has more/bigger circuitry, (it can do some more tricks than the 6D CMOS, like 3x3 pixelbinning).

[Audionut]

Yes, but a fixed ISO rating from DxO should be saying, for a constant N of photons, the 5D3 generates N electrons, and the 6D generates N electrons, at full well capacity.  By measuring the ISO at saturation, I believe this negates any influences by sensor filters.  With the sensor filter removed, this should lower the ISO rating, for the same quantum efficiency.

Since we know that even the base gains have some (ISO) headroom between the default gain, and actual well saturation (and seems to vary with camera), this should probably be taken into account.  And should drive the accuracy of the quantum efficiency results higher, since it's less affected by downstream influences. 

If you're looking at sensor efficiency, rather then camera efficiency, I guess.

[Levas]

Ah I get what you mean, the circuitry has the same effect as any difference in the color filter array.
But since things are measured with saturated pixels, the filters/circuitry don't have effect on the end results.
So the difference in full well capacity between the 5d3 and 6d is not due to difference in color filter array or circuitry.

The way Alex measures the full well capacity, what does the result mean:
-Is the full well capacity result the best possible capacity a pixel can have.
or
-Is it an average amount, like all electrons divided by the number of pixels.
?

Since I don't believe every pixel has exact the same full well capacity, or has it 
Now I think about it, maybe that's the reason why canon is staying on the save side with ISO/dynamic range.

[Audionut]

So the difference in full well capacity between the 5d3 and 6d is not due to difference in color filter array or circuitry.

No, because full well capacity is a measure of the maximum number of electrons generated.  And the photon to electron witch craft happens after the filter array.

The way Alex measures the full well capacity, what does the result mean:
-Is the full well capacity result the best possible capacity a pixel can have.
or
-Is it an average amount, like all electrons divided by the number of pixels.
?

Since the maths doesn't account for the number of pixels, I assume it's a measure of the entire sensor.
edit:  That doesn't make sense since there are significantly more pixels then the electron count.
http://www.clarkvision.com/articles/digital.sensor.performance.summary/#full_well

Since I don't believe every pixel has exact the same full well capacity 

I believe flat fields will correct variations in pixel output.

[IliasG]

....
- 6D's sensor has a higher quantum efficiency
...
Theory:
- photon to electron ratio = quantum efficiency (assumming it's a sensor constant)
- equal ISOs = equal number of photons per area (light required to saturate the sensor)
...

I think that equal ISOs = equal relative saturation (electrons counted/full saturation level ).

At least, Dxo's measures are using this 
http://www.dxomark.com/About/In-depth-measurements/Measurements/ISO-sensitivity
"... relates sensitivity to the exposure necessary to saturate the camera"

Higher QE gives higher "Dxo measured ISOs" for the same electron capacity ..

[a1ex]

Exposure, in this context, is proportional to the number of captured photons per area (in the sensor's plane). On the same sensor, this translates, indeed, to equal relative saturation (electrons counted / full saturation level), but on different cameras, at the same ISO, both sensors would saturate at the same level of incoming light (photons), if the shutter speeds are equal.

A sensor with higher QE can be used with lower internal amplification, so the ISO value measured by DxO can be lower. If QE's were equal, I expect DxO ISOs to be even lower on 6D, because the difference in electron capacity is quite high (higher than what you would get from different pixel sizes).

[IliasG]

Alex, as I understand it, DxO does not measure the amplification but the output sensitivity. i.e. for an A level of illuminance how high in the 0-1 scale (0=black - 1=full saturation) is the output in raw levels and compares it to the nominal value.

Say for the same illumination
5D4 has QE=50% and saturation at 10000 electrons/square micron. Gives as output 0.5 in the 0-1 range (white clipping level - Black level) which corresponds to 5000 electrons
6D2 has QE=55% and saturation at 11000 electrons/ square micron. Gives as output 0.5 in the 0-1 range which corresponds to 5500 electrons

the two cameras will have the same dxo-measured ISO

[a1ex]

And that level of luminance is proportional to the number of photons.

I'm not sure where you are trying to get.

[Stedda]

I'll tell you after receiving the DR test results from at least 3 more cameras,

Finally sunny after 3 days of rain and overcast/100% humidity good day for HDR... if my last attempt to help with LV Binning wasn't a dud I'll give this one a shot today. Should I bother?

[a1ex]

Last attempt to help with LV binning? Where?

I don't see much else, other than...

After looking at it I get it now.

Hope they help...

[Stedda]

I PMd you a link with a Dropbox .zip 100 megs of shots that day...

[Stedda]

Dope.. sent it to alex not a1ex

Pm comming from dummy now...

[a1ex]

Thanks, received now.

[a1ex]

Pixel binning test results moved here: http://magiclantern.fm/forum/index.php?topic=16516.msg160832#msg160832

[Stedda]

Glad it worked out... I'll do the other test and get you results for tomorrow...

[IliasG]

And that level of luminance is proportional to the number of photons.

I'm not sure where you are trying to get.

Forgive me .. while my eyes were reading "photons" my brain translated it to "photoelectrons" ..

My point is that QE cannot affect the full saturation level .. 

I will reread the thread and come back if I have something useful to say ..

[a1ex]

Yes, QE alone can't affect the saturation level, but if you increase it and you want to keep the same ISO, you will have to turn down the amplifier gains - and this increases the full well capacity.

[Greg]

500D, trying to increase the resolution of the video raw (crop mode).

Default :
http://s29.postimg.cc/ugjr8rxet/res1x.jpg

I changed (FPS timer A, C0F0[6084], C0F0[6088])
http://s29.postimg.cc/isuaryxnp/res2x.jpg

Add 512px width :
http://s4.postimg.cc/s4sbor8iz/res4x.jpg

Add 2048px and shift :
http://s16.postimg.cc/mpui9r4sz/res5x.jpg


Full width :
http://s27.postimg.cc/be7g4qaz5/full_width.jpg




Trying to change the height (photo mode):

[glubber]

Well it took me forever to realise that i had to put "image review" to "HOLD" 

But finally:

SNR for 550D ISO 100 Photomode:



SNR ISO 100 Moviemode




SNR ISO 1600 Photomode




I hope those above make sense

[a1ex]

The first image is almost perfect, the second is incorrect (very poor coverage in highlights), the third is fine, but could have better coverage in shadows.

If you can do a complete set (photo, movie 1080, movie 720, and 5x zoom), would be great.

Side note: I will also use this data for optimizing exposure choices in ETTR.

[Stedda]

A1ex, if I shot this out in the sun with a full set for 5D III would it suffice?


Spyder Cube
https://search.yahoo.com/search;_ylt=AwrBTzgKP9lTAhIA.x5XNyoA?ei=UTF-8&type=599486&fr=chr-greentree_ff&ilc=12&p=spyder+cube&SpellState=&fr2=sp-qrw-corr-top
Specular Highlights, White, Black Trap, 18% Grey

[a1ex]

I'm looking for continuous coverage from deep shadows to clipped highlights, and static scene (lack of motion or light changes is very important, so natural light variations may cause issues).

Shooting a light bulb with something dark near it, and really out of focus, should do the trick. Also Audionut explained his setup a while ago (a picture would be nice).

[Stedda]

OK, I'll put that cube next to a light bulb and lock everything down like the last test.

Any time I've used that cube I've gotten blown highlights and pure black.

[Stedda]

I setup a nice little scene to shoot yesterday but when I powered up the camera I got an API warning for RAW_DIAG version 5 expected 6... is there one online I can use?