When looking for a smartphone you may know that you want a strong battery, a good camera or a bright screen – but when you actually look for a device, all the different terms can make it seem like you’re reading a different language. We pride ourselves in developing smartphones with some of the most impressive specs on the market and so it’s important to us that we help people go behind the acronyms to understand the latest developments in smartphone technology.
This week we’re looking at ISO sensitivity in the context of smartphone cameras. ISO stands for the International Organisation for Standardisation which is a body that provides standardised measurements for different aspects of technology and business. With regards to cameras, the ISO number was originally an analogue measurement for film speed (or a film’s sensitivity to light). A higher ISO number meant less light was required to capture the same image although it also commonly resulted in grainier images.
The grain effect happened because a film’s light sensitivity was related to the size of silver halide grains in the film’s emulsion. Larger grains gave film a greater sensitivity to light but produced a grainier image. Fine-grain films, such as film designed for portraiture, needed more light but produced much smoother images.
ISO in the digital cameras in your smartphone camera works completely differently and comes with its own set of challenges. In a digital camera, a sensor turns light into an electrical signal ready to be processed. Essentially, when we’re shooting at higher ISO numbers, we’re amplifying the signal that comes from the sensor and therefore reducing the amount of light required to take quality images.
At low ISO numbers, to be able to get a good photo in low light, the shutter needs to stay open for longer so that more light can get in. If there’s any motion, or the camera is unstable, this can result in blurred images – a higher ISO means you can use a faster shutter speed and reduce the blur caused by movement. Check out the photo essay from Zoe Noble to see the kind of low light imagery than can be captured.
In Xperia Z5, the lowest ISO setting available is 50 – this will need loads of light and will result in super smooth images. The numbers then go up by factors of two (100, 200, 400 etc… all the way up to 12,800), each time you double the number, you halve the amount of light you need to take the same shot.
One of the issues with raising ISO though is that higher sensitivity can also cause blur. This is similar in some ways to when you raise the volume on a speaker and increase the potential for distortion, when you’re amplifying the signal from the sensor, there is a higher potential for graininess. The camera in the Z5 has ISO 12,800 and so the challenge for our engineers is to work out how we can use internal processing to still produce clean, beautiful imagery with such a high ISO.
The key is to remember that at ISO 12,800 you’re making an image using only 1/128th of the light that you would need if you were making the same image at ISO 100 – so everything has to work perfectly together. The lens has to suck in as much light as possible (made possible with the wide angle F2.0 G lens in Z5), the sensor has to be super sensitive and produce a really clear signal from the light that hits, and all the signal has to be treated by really intelligent software to maximise the available light.
As there are so many different elements that influence the quality of an image, one of the things we’ve worked on is the ability to achieve high quality images with mid-range ISO settings. While there’s potential to use ISO 12,800, thanks to the camera technology in our smartphones it’s easy to snap beautiful images with mid-range ISO settings.
Sony is one of the world leaders when it comes to creating sensors for smartphone cameras and the Z5 features Sony’s brand new large 1/2.3” Exmor RS™ for mobile 23MP sensor. The image processing is then all handled by Sony’s original image sensing processor.
So there you go – ISO settings, a number that helps you helps you manage the light available in your shots.