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Metering and exposure compensation on the D800...

txstone12

Texas, US
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"RE: Metering and exposure compensation on the D800..."

txstone12 Gold Member Donor Ribbon awarded for his generous support to the Fundraising Campaign 2014 Nikonian since 12th Feb 2012
Sun 23-Dec-12 10:10 PM

But, Stan…

First of all, I made the comment to Chris about ‘does operating at higher ISO levels mean we are creating more draw on the battery’? Sorry to divert you to this … ahhh, bumpy track, Chris.

Dan, this is still in the spirit of exchanging information to answer your Question 1.

I’ve spent a good bit of time trying to understand your post, Stan. I’d like to try to put it in context and understand more about how DSLRs operate at high (beyond base) ISO levels. My goal is to understand and illuminate as much as possible how ISO processing relates to Nikon and the D800. I’ve tried to limit my search to noise processing within operating ISO limits (spec values), not long exposure noise reduction. I’ve also tried to limit consideration to that processing done for a single pixel only, not software algorithms that compare pixels over an area.

What I hope to show is DSLRs perform a lot of processing to deal with the complications of noise. I also want to ask for help in finding what the D800 does in terms of NR processing. My contention (as I believe we intended earlier) is that this processing all results in low power consumption, but some power consumption.

A general observation from Nikon

"Raising ISO sensitivity amplifies the electronic signal, which also amplifies any noise in the signal; as a result, the higher the ISO sensitivity, the more obvious the effects of noise on your photographs."

http://imaging.nikon.com/history/basics/13/index.htm

As you mentioned, Stan, Nikon has developed proprietary technology, at least since the FX format CMOS sensor introduced in the D3.

"Nikon has also developed an original method for reading the amplified electrical signal — 12-channel high-speed readout. By reading electrical signals in parallel, high-speed readouts are achieved (about twice the speed of the D2X). At the same time, the drive speed for a single channel becomes inversely lower. This results in better suppression of noise generated in the circuit, and …"

http://www.nikon.com/about/technology/rd/core/optics/cmos/index.htm

A figure labeled 12-channel high-speed readout shows column amplifiers as you mention with 12 channels in parallel for signal readout.

The article below lists the four main sources of noise in DSLRs – Dark noise, Readout (aka Bias) noise, Photon noise and Random noise.

http://photo.net/learn/dark_noise/

The main point I wanted to bring up here is that the article describes
Complicating Factors:

"CMOS sensors allow the placement of both photosites and transistors on the sensor itself. (CCDs cannot have any processing circuitry built into the sensor - just transfer gates and the like, which are controlled by off-sensor control circuitry.) Because of this, CMOS sensors generally have at least the readout amplifier built in to the photosite. There may be other transistors as well, which perform other processing steps. It is now very common for a CMOS sensor to include noise-reduction circuitry directly on the sensor alongside the readout amplifier. In some designs, a sort of small dummy photosite, shaded from light, is used to quantify the likely dark noise level in the actual photosite, and this quantity is subtracted during readout. In other designs, a constant - corresponding to the tested dark current of the sensor - is subtracted from the photosite value during readout. If anything like this is happening, expectations such as "dark noise will double with twice the exposure duration" may turn out to be false."

This article goes on to say,

"Note that both of these kinds of on-sensor processing affect the camera's RAW image. That is to say, the RAW image is not necessarily "exactly what the sensor detected," as is often said. Instead, it is exactly what the sensor detected, plus or minus whatever built-in on-sensor processing is being done in that particular camera. The raw image lacks any post-readout processing, of course - the point is that on CMOS sensors some processing may be unavoidable and its effects will be present in the raw format image."

Since my primary interest is in what technology Nikon is using, that brings us to a review of the Nikon D3X. This review says that Nikon, in addition to the now familiar 12 channel readout, applies on-chip noise reduction and NR algorithms on the image processor.

http://m.dpreview.com/reviews/nikond3x

Among the Key Features are


"• 14-bit A/D conversion, 12 channel readout
• Gapless micro lens array and on-chip noise reduction
• Nikon EXPEED image processor (Capture NX processing and NR algorithms, optimized for D3X, lower power)"

The Nikon information below on both the D3S and D3X, sheds some light on the D3S

http://imaging.nikon.com/lineup/microsite/d3s_d3x/en/image_quality/
TECHNOLOGY:
"14-bit A/D conversion and 16-bit image-processing pipeline
… So, to maintain impeccable accuracy, the D3S and the D3X use 16-bit data transmission throughout the image-processing pipeline."
(More about the image-processing pipeline later)

"Advanced noise reduction at high ISO for natural-looking results
The D3S uses a newly developed image sensor, which has been refined from the D3 to further minimize noise generated by the amplified signals. This contributes to exceptional image quality and spectacular saturation, even at high ISO settings such as ISO 12800. High ISO noise reduction activates automatically when shooting over ISO 3200, minimizing mottling, color bleeding and shadow noise."

What about the current generation Nikon DSLRs, the D4 and D800/E? I haven’t been able to find much on either

D4 - Nikon's original key technology
http://imaging.nikon.com/lineup/dslr/d4/features01.htm

"Optimum use of light: Nikon's proprietary image sensor technology
Such exceptional image integrity across such a wide ISO sensitivity range is made possible through Nikon's proprietary and exclusive sensor technologies. The pixels are spaced at a pitch of 7.3 µm while gapless micro-lenses are employed, and anti-reflective coating is used on various parts – all of which results in minimized ghost and flare. This detailed design gives the D4 an unprecedented ability to channel all available light efficiently and directly into the sensor. The advantage is maintained through improved sensor quantum efficiency, ensuring optimum conversion of light into electric signals, and delivering digital files at ISO 100 to 12800 with a wide dynamic range and an outstanding signal-to-noise ratio. The benefit of a high-efficiency sensor is enhanced by an integrated approach to noise reduction. The layout of electronics within the sensor has been carefully configured to minimize noise. Despite operating at the amazing speed required to realize approx. 11 fps, the D4's image sensor consumes less power, contributing to extended battery life."

And the D800/E

Nikon’s original technology
http://imaging.nikon.com/lineup/dslr/d800/features01.htm

"EXPEED 3 image-processing engine: speed, versatility, and high performance

Even with specialized processing features like Active D-Lighting and high ISO noise reduction, capture speed is not affected."

D800 Key Features
http://www.europe-nikon.com/en_GB/product/digital-cameras/slr/professional/d800

"36.3 megapixel FX-format (full-frame) CMOS sensor with high signal-to-noise ratio, wide dynamic range and 12-channel readout."

And finally, Nasim Mansurov on the ‘image-processing pipeline’

Benefits of a High Resolution Sensor - Jan 9, 2012 BY NASIM MANSUROV
http://photographylife.com/the-benefits-of-a-high-resolution-sensor

"There is a fourth*, very important attribute that very few people mention when talking about pixels and sensors that also plays a huge role; it is the software algorithm run by the image processor that analyses the data from the sensor and runs a series of image processing steps to reduce various artifacts, reduce noise, apply sharpening and more. This is commonly called the “image processing pipeline”…"
* Pixel Size, Pixel Density, Sensor Size and Image Processing Pipeline

"But revenge and larger market capture are not the only reasons why Nikon decided to go with a 36 MP sensor on the D800, in my opinion. There are two more key factors here – high resolution sensors are cheaper to make in the long run for Nikon than low-light sensors. Sounds wrong, but Nikon spends a lot of R&D money on its noise reduction algorithms. And after spending all that time and money, it is painful to see something like the D700 cannibalize its flagship line sales. …"

So, there is a whole lot of noise processing going on, although in a low power environment. It looks like some of this processing may be performed on the EXPEED 3 processor. I would be very interested in hearing what others know about just what NR the D800 does on chip and in the processor.

Back to the list of power consuming operations. Should we update the list to include use of Live View, Stan?

David

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