You probably don't know what ISO means – and that's a problem
Whatever camera or phone you have, it’ll report the ISO value it used to take its photos. Despite its ubiquity, ‘ISO’ probably doesn’t mean what you think it does. Worse still, it may be holding your camera back, both in terms of the images it takes and in the tools it provides you. This means it's potentially holding your photography back, too. Part of the problem stems from the fact that ISO sounds like something you were already familiar with.
At first glance, ISO settings look just like the sensitivity ratings used for film (to the extent that there are some people who still refer to ASA: the US standard incorporated into the ISO standard for film). But ISO in digital isn’t the same as film. it’s essentially a metaphor for the way film sensitivity worked, if you got it processed in a minilab machine. This is a problem.
It causes confusion
The apparent familiarity and simplicity of ISO setting leads to a number of common misunderstandings. Despite what you may have heard or read, changing the ISO of your camera does not change its sensitivity.
ISO changes the lightness of the final image but it doesn’t change the fundamental sensitivity of your sensor. Nor is it an indicator of amplification being applied: although many cameras do increase their amplification as you increase the ISO setting, this isn’t always the case.
This may sound like semantic nit-picking, but it causes a lot of misunderstandings. It’s widely thought that the additional noise in high ISO image comes from the ‘background hiss and hum’ of the sensor’s amplifiers. This feels right: we’ve all heard more noise if we turn up the volume on an audio amplifier. Unfortunately it’s simply not true: most noise actually comes from the light you’re capturing, so it primarily depends on your shutter speed and aperture.
The ISO standard doesn't specify that amplification needs to be used, nor does it specify what happens in the Raw file
The ISO standard doesn't specify that amplification needs to be used, nor does it specify what happens in the Raw file. All it does is relate initial exposure to output JPEG lightness, however that is achieved. The only thing you can be sure of, at the Raw level, from an increase in ISO is that if it prompts a reduction in exposure, you'll collect less light and therefore see more noise for each tone from the scene.
There's an ISO standard that's slightly more pertinent to Raw files, which looks at when the sensor becomes completely saturated, but this doesn’t correspond to the standard used by your camera. So next time you see a graph comparing ‘Manufacturer’ and ‘Measured’ ISO, what you’re actually looking at is the ‘JPEG ISO’ vs ‘Saturation ISO.’ Any differences between the two mainly tell you how many stops above middle grey the manufacturer's JPEG tone curve is designed to deliver.
It encourages poor exposure
As well as giving a false sense of simplicity, ISO’s increasingly tenuous attempt to mimic film ratings can mean making poor use of sensor response.
Film (particularly negative film) has a very distinctive response curve that gives lots of latitude for recovering highlights. Digital is very different: it offers a much more linear response but with a hard, unrecoverable clipping point in the highlights. And no, your favorite software doesn't really recover completely clipped highlights from your Raw file*.
|This graph shows the signal-to-noise ratio (essentially the noisiness) at different brightness levels of film and digital. The film response peaks and then gradually declines, with plenty of scope for recovering highlights from the right-hand side of the curve. The digital response rises to much higher levels than the film, then cuts-off abruptly. So why would you expose these two media in the same way?
Illustration based on DxO's analysis
And yet, despite these differences, the digital ISO standard is based around ‘correctly’ exposing JPEG midtones**. A 2006 update to the standard gave manufacturers some flexibility in terms of how many stops of highlights they wanted in their JPEGs above middle grey***, but it still encourages exposure based on midtones, with a pre-set number of stops above this for highlights.
That’s not the best way to expose digital. The best results are achieved by giving as much exposure as possible without clipping the brightest tones you care about: a process called ‘exposing to the right.’ This maximizes the amount of light, and hence signal which, in turn, optimizes the signal-to-noise ratio (essentially ‘noisiness’).
And yet, by worrying about the JPEG middle grey, cameras end up giving every image the same number of stops for highlights, even though this is wasted in low DR scenes (that highlight space isn’t used and exposure is lower than optimal) or insufficient in high DR situations: the lovely colors of the sunset you’re shooting are lost, unrecoverably, to clipping.
This problem isn’t easily solved: there are times that exposing-to-the-right will result in noisier midtones than you want. In these situations, you have to let the highlights go. However, fixating on JPEG midtones isn't helpful.
It warps camera development
This brings us to the biggest problem with using a clumsy metaphor for film sensitivity as the way of setting image brightness in digital: it means we aren’t given the tools to optimally expose our sensors.
ISO ends up conflating the effects of amplification and of tone curve, meaning you have to do your own research to find out what your camera’s doing behind the scenes, and what the best way to expose it is.
We aren’t given the most basic tools: Raw histograms or Raw clipping warnings that would help optimize exposure
The preview image your camera gives, the histograms it draws and the exposure meters and guides it offers are all based on JPEG output and their midtones, because ISO says that’s what matters. This means we aren’t given the most basic tools we need: Raw histograms or Raw clipping warnings that would help optimize exposure. It means no development has been done to create more sophisticated tools that would help you judge the quality implications of exposing to the right, and when to let the highlights go.
In short, ISO is an increasingly shaky metaphor that promotes misunderstanding, obscures what your camera is doing and robs us of the tools we need to get the most out of our cameras. Isn’t it time for something better?
* Highlight recovery sliders usually rely on only one of the color channels having truly clipped, and try to guess the value of the clipped channels, based on the remaining, unclipped one, so tend to be limited in their effectiveness. [Return to text]
** We put the word "correctly" in inverted commas because the more you think about it, the harder it becomes to pin down what 'correct' exposure might be. If you're certain that you know what 'correct' exposure means, then you should probably check through the assumptions that underpin it. [Return to text]
*** This change is why the JPEG ISO ratings used by manufacturers don’t need to coincide with clipping-based Raw ISO numbers. We’ve previously written an article about how it works. [Return to text]
|Lake Louise by MIRANDA1|
from blue challenge
|Looking for dinner!!! by Chairman1|
|Peony by jalywol|
from Flowers up close.
The Google Pixel 4 will likely launch with an astrophotography feature, HDR in the preview image and a range of other new imaging functions.
In the first part of his series, landscape photographer Erez Marom starts with the very basics of drone photography – namely, what a drone is and how it works.
Blackmagic has announced an update to Blackmagic RAW that adds support, via plugins, to Adobe Premiere Pro and Avid Media Composer. Blackmagic also announced a pair of Video Assist 12G monitor-recorders with brighter HDR displays, USB-C recording and more.
This week Chris and Jordan review the new Canon EOS M6 II mirrorless camera. Even if you're not interested in the camera, you should probably watch just to see Jordan sing a Dire Straits cover.
A new gallery from the Canon EOS M6 II, shot by Chris and Jordan while filming this week's episode of DPReview TV. As usual, it comes complete with reflected images in puddles.
STC Optics announced new filters for Panasonic Lumix M43 camera systems, Z Cam E2 4K Cinema Cameras and Blackmagic Pocket Cinema Camera 4K units.
Atomos continues its partnership with camera manufacturers to get the best image possible from the sensors inside the latest camera systems.
Sony has announced the impending arrival of its next-generation video camera system, the FX9. The full-frame E-mount system is set to be released later this year with a 16-35mm E-mount lens to follow in spring 2020.
Slow-mo videos are awesome on their own, but have you ever wondered what 72 slow-mo cameras are capable of producing? Well, wonder no more.
Google uses machine learning to pick your best photos from previous years and pins them to the top of your gallery.
The new tool uses AI and machine learning to automatically reframe video sequences to fit different aspects ratios so a single video can easily be edited for publishing on multiple platforms.
The Canon RF 85mm F1.2L USM is one of the most impressive lenses released for the nascent RF system, and we've just updated our gallery of sample images.
The new calibration systems are designed to work with bright HDR monitors and OLED screens of every shape and size.
The XEEN CF lenses will be offered in 16mm, 24mm, 35mm, 50mm, and 85mm options for Canon EF, Sony E and PL mounts.
It's an extremely minor firmware update, but it's better to be safe than sorry. The last thing you want is to have to stop mid-shot in the field to address a little software glitch.
After a string of so-so entry-level ILCs, Fujifilm appears to have pulled out all the stops with its new X-A7.
The Fujifilm X-A7 is the newest addition to the company's X-series lineup. Despite its relatively low price of $700 (with lens), Fujifilm didn't skimp on features. Click through to find out what you need to know about the X-A7.
The entry-level Fujifilm X-A7 improves upon many of its predecessor's weak points, including a zippier processor, an upgraded user experience and 4K/30p video capture. It goes on sale October 24th for $700 with a 15-45mm F3.5-5.6 kit lens.
LaCie has announced a trio of SSDs with ruggedized protection for the harshest of environments.
Irix says the new lens is designed for 8K recording and features a cinema-specific optical construction.
The update brings hundreds of bug fixes, a new Film Negative tool and support for rating images.
The a7R IV represents our first chance to analyze Sony's new 61MP backside-illuminated sensor. Take a look at what it's capable of.
The delays will only affect shipments to Japan, according to a Venus Optics spokesperson.
Sony's habit of giving similar names to cameras that look the same can make it difficult to choose between them. We've broken down the differences and how they compare to their rivals.
Robert Frank's unconventional approach to photography and filmmaking defied generational constraints and inspired some of the most influential artists of the 20th century. He passed away today at age 94.
Sigma is getting serious about cinema with its classic-inspired lens lineup, updated cine primes and a new PL to L mount adapter that's in the works.
All three devices offer a standard 12MP camera plus, for the first time on an iPhone, an ultra-wide 13mm camera module. The 11 Pro and 11 Pro Max also retain the telephoto camera of previous generations.
The new Huawei mobile chipset offers hardware noise reduction among other new imaging features.
The Polaroid Originals is effectively a modernized version of its 'Impossible Lab' first released back in 2013.