The Raw and the cooked: pulling apart Sony's Raw compression
|Raw compression won't be apparent in every image, but there are circumstances in which it risks undermining what should be a great image. Photo by Rishi Sanyal|
Update: September 15, 2015: Sony has announced that the a7S II will have the option to shoot uncompressed Raw, with firmware being rolled out for some existing models, including the a7R II used here, later.
A Raw file is a Raw file, right? Well, not exactly. Lately, there's been a lot of talk (and a lot of anger) about the compression Sony uses in its Raw files. Compressed Raw files aren't uncommon, but they're usually compressed in a way that retains all the original 'raw' data from the sensor. Or, at least, all the information that's visually meaningful.
Instead Sony has, for several years now, chosen to apply non-optional lossy compression to its Raw output. This isn't likely to be an issue for many users, since the impact is generally quite small, but as the company shows its ambitions in the high end market, with the launch of the a7 series and a dedicated support system for professionals, the impact on image quality deserves a little scrutiny.
What exactly is going on with Sony's Raw files, and what might the potential impact be? The compression system has been investigated and detailed by Iliah Borg and Alex Tutubalin, and we've tried to distill their findings. It's important to keep this in perspective, though: in many circumstances you won't see this impact or encounter the limitations it can impose.
Sony's compression process has two parts, and each of the two aspects have a different impact on the Raw files. The first step applies a compression curve to the data. This is a bit like a tone curve and is used to map the 14 bits of captured data down to an 11-bit space.
Although this part of the process is lossy, a well-designed compression curve has little to no impact on image quality. This is because although shot noise makes up a decreasing proportion of the captured data in bright regions, the actual magnitude of the noise increases. This means it doesn't make sense to retain all the information about bright regions of the images, since a lot of that information will just be recording the subtleties of the noise.
Ideally, then, you can get away with a lot of compression in bright tones so long as you preserve increasing amounts of information at the dark end of the file. Unlike the (optional) compression curve Nikon uses, Sony's doesn't fully exploit this phenomenon, meaning that some useful data is lost, as well as some of the noise. This will, theoretically, reduce the dynamic range available in the files.
Sony's Raw compression then has a second stage, where the image is divided up into a series of 16 pixel stripes for each color channel. Rather than recording a separate value for each of these pixels, the Sony system records the brightest and darkest value in each stripe, and a series of simple notes about how all the other pixels vary from those extremes. These notes are recorded using fewer bits than it would take to record the actual pixel values and it's this step that appears to cause most of the problems.
When there's not much difference between the brightest and darkest pixel, the system is able to describe the scene pretty well. However, as soon as you have a big gap between bright and dark, the 7-bit values used to note the differences aren't sufficient to precisely describe the original image information.
This imprecise recording of the original image data leads to artifacts in stripes around high-contrast edges in the photos. These errors can become even more pronounced if you increase the brightness or contrast in those regions when processing the files.
14-bit and 12-bit readout
To compound matters, several Sony cameras we've tested appear to switch their sensor read-out from 14 bits to 12 bits in certain modes: further reducing the amount of dynamic range that the camera ever captures, even before the effects of the compression process are brought into play. Continuous shooting, Bracketing and Bulb exposure modes will all push most Sonys down to 12-bit capture mode, which is then subjected to the two stage compression.
This only really matters at base ISO however, since that's the only time you're likely to capture more dynamic range than a 12-bit file can accurately store.
These approaches probably made sense in consumer-grade cameras, back in the days where processing power and storage space came at a significant premium. However, on a camera as expensive as the a7R II, which is likely to be used for quality critical shooting, it's hard to justify clumsy compression that can, depending on the image, throw away data you were expecting to have access to.
Overall, the effects of this compression aren't often visually significant. Their impact should mostly be understood as a reduction in processing latitude, since it tends only to be when you push and pull the Raw files that the missing data becomes visible. The compression curve throws away more shadow data than would be ideal: reducing dynamic range. There's a further reduction if you shoot in a mode that drops the camera into 12-bit readout mode. Meanwhile, the localized compression of tonal differences only has an impact near high-contrast edges.
|And it's not just heavily-pushed images that start to reveal the lost data: this is a straight out-of-camera JPEG file (shot with DRO Auto), still showing stripes extending from a high-contrast edge. It looks still worse in a gently processed Raw conversion.
It's worth noting, though, that the impact of this process is lessened in the company's higher pixel-count bodies, since a 32-pixel stripe will be a smaller proportion of the a7R II's 40MP images than it would in a 12MP image from the a7S.
It's quite possible to shoot for years and never notice the impact of these design choices Sony has made, but they do add up to mean that you can't access the full capability of the camera. Most people shoot Raw precisely because they want to preserve the maximum possible processing latitude and keep their creative options open. Raw compression isn't the end of the world by any means, but it throws away a little bit of a camera's capability, which might be a little hard to swallow if you've paid multiple thousands of dollars for a cutting-edge camera.
|CZ54-1-2 by TrickTheLight|
from anything you can do I can do better
|Fork-tailed Sunbird On Ivory Coral Tree by cntlaw|
from A big year - birds 2019
|Washing day by Jill Hancock|
from -Minimum Wage- (non-human shot in Full Colours Only)
Night Sight, Portrait Mode and (surprisingly) wide-angle selfie mode are features that we're currently loving about the Pixel 3's camera.
The Auschwitz Museum has asked visitors to be more respectful after an upsurge of pictures posted on social media showing people posing on the train tracks that lead to the main gate.
This week Chris and Jordan take the new Leica Q2 for a spin, and while most of us in the Northern Hemisphere are welcoming spring, they head even farther north than usual to visit ice castles. Because #Canada.
Harvard is facing a lawsuit over profiting from 19th century daguerreotypes that captured the portrait of a slave and his daughter on a South Carolina plantation.
From the detailed textures in rural landscapes to the incredible lighting inside futuristic buildings, the photorealism of Unreal Engine 4 is blurring the lines between fiction and reality...you know...aside from the spaceship.
According to a report from The Informant, a number of Instagram users' passwords were shared as plaintext in URLs used to download their data.
We've added Panasonic's new Lumix S1 and S1R full-frame mirrorless cameras to three of our buying guides. If you're looking for a quick summary of each model, then have a read.
YouTube channel Photoshop Cafe has shared a video detailing ten tips and tricks you can do to both fix and speed up Photoshop when it's running slow and sluggish.
It's not going to be the banger of the year, but it'll get a few laughs.
DJI has confirmed its drones won't be affected by the GPS 2019 week rollover.
Dogfish Head Craft Brewery has teamed up with Kodak to release a beer that's capable of doubling as a film developer.
The Diana Instant Square is a retro-inspired camera with manual controls that's fun to shoot in good light, but largely unpredictable in its operation.
Residents of a Paris street plagued by Instagrammers, selfie takers and music video crews are asking the city government for a weekend and evening ban to give them some peace.
The adapter plugs into the Osmo Pocket's USB Type-C port and features a 3.5mm TRS jack to plug in various external microphones.
Checkout allows Instagram users to select products for purchase and make payments directly in the app.
GauGAN as it's known, can create photorealistic images from basic drawings using the power of artificial intelligence.
The EOS RP is Canon's latest full-frame mirrorless camera, with diminutive dimensions and a diminutive price. Find out how it stacks up and get our thoughts in our early review.
Montana judge Dana L. Christensen has ruled the Republican National Committee did not infringe upon the copyright of photographer Erika Peterman after they took a photo from a Democratic candidate's Facebook page without permission and altered it to use in a derogatory promotional mailer.
Nikon has launched updates for three of its programs to address various bugs and glitches that could cause crashes and unwanted results.
LEE Filters has launched the LEE100, its next-generation filter holder that improves the design and looks in all the right places.
With the arrival of some much-needed sunshine and final production firmware for the Panasonic S1, we've been able to get outside and really start putting the camera through its paces.
Importing, culling and tagging photos is about to get a whole lot faster and look a whole lot better with the impending arrival of Photo Mechanic 6.
On its own, the FTZ adapter retails for $250 and when bundled it dropped the cost to just $150. Now, Nikon is offering it for free with all Z6, Z7 purchases in the United States.
Profoto said it spoke with Godox back at Photokina 2018 and continues to contact Godox in an effort to stop it from marketing its V1 light.
Product renders in Italian publication Notebook Italia show an unusual design that conceals all cameras with the help of a slider mechanism.
Canon says its new EF 400mm F2.8L IS III and EF 600mm F4L IS III lenses can suffer from an intermittent flickering when shooting video in M or Av modes with certain cameras.
Leica recently announced the Q2, a digital rangefinder with a fixed 28mm F1.7 lens. It's a heck of a lot of fun to shoot with, but is it right for you? Based on our time with the camera, and its specifications, we've examined how well-suited it is for common photography use-cases.
Now that our Panasonic Lumix S1R has final firmware, we couldn't wait to get out shooting with it - and we also tried the high-res mode, which combines files to get 187 megapixel images. Because sometimes, 47 megapixels just isn't enough.
In this article, travel and landscape photographer Mitch Green encourages us to spend more time in the the field.
the lens lacks any electronics whatsoever and is constructed entirely of glass and metal. Of course, that comes at the expense of weight — this thing weighs in at 1.1kg / 2.43lbs.