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|Shooting this image in 14-bit helped retain the full dynamic range captured by the sensor. Most of the time, with most cameras, 12-bit is enough.|
Raw bit depth is often discussed as if it improves image quality and that more is better, but that's not really the case. In fact, if your camera doesn't need greater bit depth then you'll just end up using hard drive space to record noise.
In fairness, it does sound as if bit depth is about the subtlety of color you can capture. After all, a 12-bit Raw file can record each pixel brightness with 4096 steps of subtlety, whereas a 14-bit one can capture tonal information with 16,384 levels of precision. But, as it turns out, that's not really what ends up mattering. Instead, bit depth is primarily about how much of your camera's captured dynamic range can be retained.
Much of this comes down to one factor: unlike our perception of brightness, Raw files are linear, not logarithmic. Let me explain why this matters.
The human visual system (which includes the brain’s processing of the signals it gets from the eyes), interprets light in a non-linear manner: double the brightness of a light source by, say, turning on a second, identical light, and the perceptual difference isn’t that things have got twice as bright. Similarly, we’re much better as distinguishing between subtle differences in midtones than we are vast differences in bright ones. This is part of the way we’re able to cope with the high dynamic ranges in the scenes we encounter.
Digital sensors are different in this respect: double the light and you’ll get double the number of electrons released by the sensor, which results in double the value generated by the analogue-to-digital conversion process.
|This diagram shows how the linear response of a digital sensor maps to the number of EV you can potentially capture. Note how the brightest stop of light takes up 1/2 of the available values of your Raw file.|
Why does this matter? Because it means that half the values in your Raw file (the values between 2048 and 4096 in a 12-bit Raw file) are devoted to the brightest stop of light you captured. Which, with most typical tone curves, ends up translating to a series of near-indistinguishably bright tones in the final image. The next stop of light takes up the next 1024 values, and the third stop is recorded with the next 512, taking half of the remaining values each time.
In a typical out-of-camera JPEG rendering, the first ~3.5EV are captured above middle grey, and the first three of these stops of highlights have used up 7/8th of your available Raw values. The remaining Raw values are used to capture tones from just above middle grey all the way down to black.
|Using the D750's default JPEG tone curve as an example, you can see that around 3.5EV of the camera's dynamic range is used for tones above middle grey. 1/2 the Raw values are used to capture the tones that end up being JPEG values of roughly 240 upwards, and more than 7/8ths of the available values on tones about middle grey.|
Follow this logic onwards and you’ll see that the difference between 12 and 14-bit Raw has less to do with subtle transitions* (after all, even in the example I describe, the tones around middle brightness would be encoded using 256 levels: the same number of steps used for the entire dynamic range of the image if saved as a JPEG or viewed on most, 8-bit monitors). Instead it has much more to do with having enough Raw values left to encode shadow detail.
It's a different story for files that have been processed, either by gamma correction (eg JPEGs and TIFFs) or compressed Raw files, but for linear Raw files, that's how things work.
|By the time you've created a JPEG, the brightest stop of your image is likely to be made up from the tones in this image. Half of your Raw file was used for storing just these near-white tones.|
Since every additional 'bit' of data doubles the number of available Raw values, but the brightest stop of light takes up half of your Raw values, you can see that all of those additional values increase the capacity of your Raw file by 1EV. Which, assuming neither you nor your camera's exposure calibration are completely mad, ends up meaning an extra stop in the shadows.**
|A 14-bit Raw file won't generally give extra highlight capture, it'll mean having sufficient Raw numbers left to be able to capture detail in the shadows. And if your camera is swamped by noise before you get to 14EV (most are), all this extra data will effectively be used to record shadow noise.|
In other words, 12-bits provides enough room to encode roughly 12 stops of dynamic range, while 14 bits gives the extra space to retain up to around 14EV. Or to look at it from the opposite perspective: if your camera is overwhelmed by noise before you get to 12 stops of DR, you don’t benefit from more bit depth: all you’d be doing is capturing the shadow noise in your image in greater detail.
Bit depth in video
It's a similar story in video. Because video capture is so data intensive, it’s not usually practical to try to save all the captured data, which usually means crushing everything down to just 8 or 10 bits.
Log gamma is a way of taking the linear data captured by the sensor and reformatting it so that each stop of captured light is given the same amount of values in the smaller file. This makes more sensible use of the file space and retains as much processing flexibility as possible.
And, even if you own, say, a Sony a7S (one of the few cameras we’ve encountered that has sufficiently large/clean pixels that it doesn't have enough bit depth to capture its full dynamic range at base ISO), you need to remember that you only get the camera’s full DR at base ISO. As soon as you increase the ISO setting, you'll amplify the brightest stop of captured data beyond clipping, such that you very quickly get to the stage where you’re losing 1EV of DR for every 1EV increase in ISO.
So, even though you started with a camera whose DR outstrips its bit depth, that stops being true as soon as you hike up the ISO: instead you just go back to encoding shadow noise with tremendous precision.
Consequently, if your camera doesn’t capture more than 12 stops of DR, you probably shouldn’t clamor for 14-bit Raw: it's not going to increase the subtlety of gradation in your final images (especially not if you're viewing them as 8-bit). All those extra bits would do is increase the amount of storage you're using by around 16% with all of that space being devoted to an archive of noise.
* As Emil Martinec beautifully illustrates: if the variation due to noise is greater than the steps in your sampling, the noise will dither any transition or gradient. Or, looked at the other way around: if the steps you're capturing your tonal information with are smaller than the variations caused by shot noise, there's no further gradation benefit to sampling with higher precision (you just end up perfectly describing the noise). This is exploited by some of the cleverer Raw compression methods, but that's an issue for a separate article. [Back to text]
** The best noise performance is achieved by making the most important tones in your image from as much light as possible. Which means the best thing to do if you suddenly gain an extra stop of highlight capacity is to increase your exposure by 1EV. Your highlights still clip at the same point but all your midtones and shadows receive more light and become less noisy. [Back to text]
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The Everyday Sling might just be the perfect pack for not carrying too much gear, combining comfort with Peak Design's signature modern style.
When the Fujifilm X-T2 arrived, it was more than just a modest upgrade to the already impressive X-T1. While the new X-T3 hasn't changed the overall design of the camera, this model is way more than an upgrade; rather, it's a quantum leap.
The Movie Maker is a compact, motorized slider designed for phones, action cams and small mirrorless cameras. We think it's a fun little kit and a good value proposition for the cost, provided you can work around a few of its weak points.
Nikon's Z7 is the first camera to use the all-new Z-mount, the company's first new full-frame mount since 1959. We've put together our first impressions based on quality shooting time with a pre-production camera - check out what we've found.
What's the best camera for a parent? The best cameras for shooting kids and family must have fast autofocus, good low-light image quality and great video. In this buying guide we've rounded-up several great cameras for parents, and recommended the best.
What's the best camera for shooting landscapes? High resolution, weather-sealed bodies and wide dynamic range are all important. In this buying guide we've rounded-up several great cameras for shooting landscapes, and recommended the best.
What’s the best camera costing over $2000? The best high-end camera costing more than $2000 should have plenty of resolution, exceptional build quality, good 4K video capture and top-notch autofocus for advanced and professional users. In this buying guide we’ve rounded up all the current interchangeable lens cameras costing over $2000 and recommended the best.
|The Lone Photographer by ed rader|
from My Best Photo of the Week
|_ERN9064 by ernesto juarez|
from Shoot yourself ! (with your camera)
|Neighbourhood Watch by Stevie Boy Blue|
from Zoo trip ~ Cute...
GoPro has announced its HERO7 camera lineup. The updated action cameras feature new HyperSmooth and TimeWarp modes, as well as improved video and photo specs.
The latest Samsung midrange smartphone offers a super-wide-angle lens in its triple-camera setup.
The Sony 24mm F1.4 is the latest lens to join the company's premium G Master lineup. We've been shooting with one for a couple of days - here's what you need to know.
Apple released iOS 12 a few days ago and some iPhone X users are less than happy with how the new operating system has made their phones look.
Camera bag manufacturer Lowepro has introduced mark II backpacks for its ProTactic AW range with models that are said to feature an improved handling experience as well as a collection of accessories that can be attached to the outside.
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Cosina has announced its eighth lens designed specifically for Sony's E-mount system. The Voigtlander 21mm F3.5 lens is due out October 2018.
Sony has taken the wraps off of its new 24mm F1.4 GM full-frame lens, which the company claims is the lightest in its class. Despite its fast aperture, the 24mm F1.4 is remarkably light, weighing just 445 grams (15.7 ounces). The lens will set you back $1400 when it ships next month.
In this episode of DPReview TV we take a look at Sony's brand new 24mm F1.4 GM lens, a desirable focal length for many photographers. How does it perform? Chris and Jordan give us their first impressions.
We've had a little time to shoot with Sony's new wide/fast prime, both close to home and on the water in San Francisco. Check out our initial sample images.
Fujifilm released a firmware upgrade for its X-T3 mirrorless camera that addresses issues with distortion compensation and the mechanical lock on SD cards.
The app's algorithms have been trained using using 200 million cropping data points from real photographers.
Thanks to a software update, the Loupedeck+ editing console can now be used for video editing.
British photographic engineer MTF Services is claiming the world’s first third-party lens adapters for the new Nikon Z system with a collection of four units designed to allow cinema lenses to be mounted on the mirrorless full frame bodies.
Think Tank Photo has updated its line of heavy-duty rain covers and introduced a new, compact version for emergency situations.
The X-T3 is our first opportunity to analyze what's likely to be Fujifilm's next generation image sensor. Take a look at how it performs next to the competition in our studio test scene.
Canon's new normal is seriously sharp wide open. After shooting with it for a few days, we've prepared a gallery of real-world sample images.
Nikon will cease offering Brazil-based customer service and technical support, though the company stresses that it will still offer technical assistance and warranty repairs for valid warranties.
Two years ago, CatLABS of JP announced a plan to save Packfilm from the dead. Now, it's announced it's giving up its efforts to better focus its resources elsewhere.
The GoPro Fusion is designed to make it easy to capture 360-degree video and stills. We took it out recently on a typically hot Seattle summer day to see what it can do.
We've got our hands on a full-production Nikon Z7 camera and have updated our gallery with additional samples.
A new Kickstarter campaign seeks funding for Chroma Chrono, a programmable RGB camera flash that emits multiple colors during long exposures.
Think Tank Photo has launched a new lineup of six dual-access, water-resistant protective lens cases it calls Lens Case Duo.
Canon and Nikon finally entered the full-frame mirrorless market this summer with the brand-new RF and Z mounts. Now that we've had some time with the cameras, we wanted to revisit our earlier predictions and take stock.
The devices' camera specs look pretty much identical to last year's iPhone X but under the hood a number of important improvements have been made.
Blackmagic Design has announced the public beta of its new Blackmagic RAW video codec. The company says the new format combines the benefits of shooting Raw video with the ease of use and smaller file sizes usually associated with non-Raw video files.
Serif, the company behind the Affinity suite, has announced the latest update for its mobile Photoshop competitor Affinity Photo for iPad.
The Atomos Ninja V external video recorder and monitor will be ready to ship at the end of this month. The 5.2in Ninja V is designed to provide a smaller option, while still offering many of the features of the larger 7-inch models.
Having shot with the camera, spoken to Canon and read the tea leaves, here's what DPR Technical Editor Richard Butler thinks the EOS R tells us about Canon and the RF's mount's future.
After last week's teaser, lighting manufacturer Profoto has announced its 'small big' new product. The B10 is designed to be used as studio flash head but in a very small body, and has a powerful continuous light source for videographers as well.