Tuesday, August 19, 2014

Nikon D810 High ISO and Fixed Pattern Noise (Updated)

Though the Nikon D800 was arguably already the best camera on the market from an image-quality standpoint, the natural progression of things means that the D810 has been tweaked somewhat. The most significant improvements come for videographers with the lower base ISO.... but that won't stop traditionalists from asking: "How is the high ISO image quality?"

It's fine, thank you very much.

Aug 2014 (Update 1): Nikon has now issued a service advisory for bright pixels accumulating during long exposures. See the follow-up below for details. 

Aug2014 Update (2):  An example of a post-service advisory unit.

High ISO: JPEG and NEF

The following is an ad hoc demonstration of the camera's JPEG and NEF output quality through the higher (reasonable) ISO range. The test target is a pair of Coke/Pepsi pop refrigerators situated just outside the local camera store. Taken with the AF-S 50mm f/1.4G at f4. The NEF samples are run with default Capture NX-D settings

 Pay attention to the legibility of the soda bottles for detail retention (or lack thereof) as the ISO value rises, speckling in the broad colour patches for overall image noise, as well as the harshness of the reflections and shadows as dynamic range decreases. Note that this series of images is not directly comparable to other samples on this blog, as the atrium in which this was shot has a skylight and therefore variable lighting conditions. As well, these samples will appear visually cleaner than other samples on this blog taken with lesser-megapixel cameras, as the effective object magnification is higher due to the D800's pixel count. (Click on each image for 100% crop view.)

ISO 1600
ISO 3200
ISO 6400
ISO 12800

The comfort point will vary according to your needs, but for non-professional users, the point at a photographer would not want to go any higher for quality shooting would probably be ISO 3200. ISO IS quite reasonable and would be useful in situations with carefully controlled lighting and mindful post-processing. ISO 12800 does show a distinct degradation in image quality, but is rescuable for applications where the image is downsized.

Though side-by-side images are not available, the removal of the optical low-pass filter does make images from the D810 appear sharper and more contrasty than the D800. In practical terms, it means that you need a lighter hand with sharpening the files in post-processing. The JPEG engine appears to have been improved from the D800; as you can see in  the samples above, the JPEG rendering is generally better than an un-optimized NEF conversion.

It's still early days with Capture NX-D. There's a misconception amongst hobbyists that RAW is better than JPEG. That is only true when you understand the RAW converter and how to get the result that you want out of it. "RAW is better than JPEG from a flexibility standpoint" is a more subtle ascertain. In all honesty, the Capture NX-D work-flow and overall program layout will not encourage the timid to explore that difference. Capture NX-D is very obviously Silkypix with Nikon's rendering engine. Though reception has been generally negative, its a program that deserves some patience because of the simple fact that its the only game in town if you want a convert that reads all of the proprietary information in the D810 NEF file properly.

(For a look at how the D810 stacks up against the D750 and Df at high ISO, go here.)

Fixed Pattern Noise:

What we call image noise is actually composed of a number of different factors. Fixed pattern noise (read noise, dark current, etc.) is an innate property of the sensor itself. The majority of what is perceived as image noise comes from shot-noise, which is a result of the quantum property of the income light itself.

Read Noise

Read noise is a result of variations being introduced into the data as it is read off of the sensor. You can isolate it by taking an exposure with the body cap on at the fastest possible shutter speed. In the following example, the texture of the read noise is amplified by shooting at a higher ISO and further pushing the exposure in post processing:

ISO 12800, 1/8000s pushed 5EV, 100% crop view

This is a very clean sample. Even with the exposure pushed, the image is still relatively dark. The noise pattern has a fine texture that is a bit on the tight side. This is how the D810 sensor is able to improve on low ISO dynamic range over the D800; reducing read noise helps to lower the "noise floor", allowing for a larger light well capacity to create a well-exposed image.

Amp Glow and Dark Current

This is a similar exposure, only 1 second long and pushed 9EV. This amount of over-exposure would be beyond all practical use, but it does illustrate what's going on with the sensor as a whole. You can make out higher levels of noise along the bottom and left edges of the image, as well as at the upper right corner and in a fewer streaks. The brighter edges are a result of amp-glow, which is the effect of heat on the periphery of the sensor.

ISO 12800, 1s pushed 9EV
9EV push, 100% crop

Even with the longer exposure, the texture of the noise pattern has a fine grain to it, and is free from intrusive splotches. Low dark current and amp noise are important for video output; given the D810's video focus, its not surprising to see this (well controlled) behaviour of the senor.

Long Exposure Noise

Continuing on with the issue of amp glow, this is an example of the thermal noise that is generated with a 30s exposure. The first is a 100% crop;  ISO 6400 exposure. This is analogous to a typical nighttime tripod shot taken with a wide angle lens. (Long exposure noise reduction off, naturally.) Click on image to see actual pixels.

August 2014 Update (1)

Nikon has issue a service advisory for early unit D810's regarding the phenomenon of bright pixels developing on long exposures:

"We have received a few reports from some users of the Nikon D810 digital SLR camera indicating that noise (bright spots) are sometimes noticeable in long exposures, and in some images captured at an Image area setting of 1.2× (30×20).

After looking into the matter, we have determined that some noise (bright spots) may on occasion be noticeable when shooting long exposures, and in images captured at an Image area setting of 1.2× (30×20).

Nikon service centers will service these cameras that have already been purchased as needed free of charge to the customer. We sincerely apologize for any inconvenience this issue may have caused. 
Identifying affected productsTo check whether or not your camera is one of those affected by this issue, please click the Affected Product Serial Numbers link below and enter your D810’s serial number as instructed. Your camera’s serial number will be checked against those of affected products. If your camera is one of those affected, you will be forwarded to additional instructions. If your camera is not one of those affected, you may continue using your camera without concern for this issue."

Though a number of shooters have identified it, the issue has been a hot topic of discussion over at Nasim Mansurov's Photography Life blog. The pertinent points are:

  • This is an issue that predominantly affects night photographers, and especially those who need to do work with long exposure noise reduction turned off. The implications for daytime photography is minimal to none.
  •  The effect is of fine white grains spread across the image, visible at low ISO. This is unusual to see, as it is normally eliminated in the image processing pipeline before the image file is written.
  • If you shoot with long exposure noise reduction turned on, you will not see it.
  • The fix is to send the camera back to Nikon for what is essentially a hot-pixel re-map. This process cannot be done with a simple firmware upgrade.
  • Though it is embarrassing to Nikon after the D600 saga, it is a relatively minor software fix.(Hopefully.) The issue would have received far less attention were it not for Nikon's previous handling of quality control issues. The problem with modern camera manufacturing is that software is the very last thing that is finalized; hence, the frequency that you see models requiring firmware updates within a short time of release.

Nikon has apparently changed course after the D600 and is now responding quickly to issues brought up by users. The response to the D810 thermal noise issue is about as fast as you would expect from any of the other manufacturers. This is a positive step, but given the nature of the internet and the public relations shortfall that was the D600, it will require many more positive steps on the part of Nikon to firm up consumer confidence. 

August 2014 Update (2)

Here is an example of a field unit that was sent back to Nikon and corrected with updated firmware/pixel-mapping. Note the black dot in the recess of the tripod. mount. It has the unfortunate look of having been applied with a black permanent marker, but it is a definitive visual differentiator from the uncorrected units.

The firmware for the update is version 1.01.

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