70D Dynamic Range is actually great, despite what DXOMark says

Started Jan 21, 2014 | Discussions thread
David Hull
David Hull Veteran Member • Posts: 6,387
Re: 70D Dynamic Range is actually great, despite what DXOMark says

aftab wrote:

David Hull wrote:

Just another Canon shooter wrote:

David Hull wrote:

So here is a question for you: As you say, the effective system noise (camera noise, if you will) is higher at ISO 100, so tell me how Canon would fix it. in other words, based on the DxO data and the Sensorgen information based on it, what part of the Canon architecture needs to be improved?

I called that read noise, not system noise, and they should improve the readout circuit. It is trivial and not worth discussing.

When you measure it, you do not know where it is coming from (but we have additional info indicating what is going on). What Sensorgen does it to model it as additive noise and a multiplicative one, and fit a curve. Then they report the additive noise as "read noise".

He isn't really modeling anything, he is taking the DxO information and presenting it in a different perspective, one which makes it a bit easier to see what is really going on in the camera. It is certainly read noise but it is not coming from the sensor, it is not trivial and it IS worth discussing for those who want to understand what is really going on in the camera. If you want to understand that DxO DR curve and why it looks the way it does, you have to take the time to understand the camera's electrical implementation, the noise line up etc.

I think one of the things that Canon grapples with is that they do have a very good sensor technology (and have had it longer than anyone else). Their chosen implementation is sub par to the competition in two areas which manifest primarily at low gain settings. However, at the other end (where probably the bulk of people use the camera) they are fine.

Some of us want to know the why behind the what, for those it probably IS worth discussing. My point was simple, the sensor is just part of the imaging system, and in the case of Canon, it does not appear to be the root cause of the low ISO deficiencies that everyone like to point out in these threads.

Emil Martinec in his 2008 article shows what you two are discussing about. Read noise coming from circuitry upstream of the ISO amplifier ( I think this is what you are calling sensor read noise) and read noise coming from circuitry downstream of ISO amplifier. Canon seems to have problem with the later part. Sony and other manufacturers (Panasonic, Toshiba etc) have addressed this with on chip column parallel ADC. From memory Canon has a patent for on chip column parallel ADC since 2007. My feeling is that they haven't implemented it yet because they want to refine the technique as much as possible, add newer innovations and wait for the time when it would be cost effective.

Some have postulated that they cannot implement it within their own fab.  I suspect we will see something from Canon in the not too distant future.  I doubt that they are going to like giving up this spec to Sony for long.  Exactly what they do is the question.  I think that what keeps them going is that their current architecture is good enough since more people are concerned about clean performance at the high end.  If the press is to be believed though, the new Nikon may be applying pressure on that end now.  With an ISO rating of 400k+, 25600 is probably pretty impressive.

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