Product Teardown 20 Performance of Smartphone Camera

People use different kinds of metrics/criteria when evaluating smartphone cameras, such as speed, performance, photo quality, modes, easy to use, etc. However, people are often talking about different things when they use the same words. For example, performance might mean photo quality for one group of people, but speed for another group of people.

I think its important and useful to make things clear and understand them in a little bit more detail.User research tells us that photo quality, performance and power consumption are three most important perceptions when user use a smartphone camera. In this article, I will focus on performance, and will address photo quality and power consumption in the following product teardown posts.

What does performance exactly mean?It usually means how fast you can take and get a photo. Well, you could argue that if your camera can take good photos in very low light performance, it has good performance.

But that is more in the photo quality arena. So I will leave the discussion to photo quality post.What exactly happened when you take a photo?

From users perspective, taking a photo is so easy: just open the camera and press the shutter. Done. Actually, a series of actions happened when you take a photo.

Open camera app -> see the object in Viewfinder ->adjust the view finder, press shutter ->AF lock down ->shutter release -> shutter close -> see the snapshot on display or see the thumbnail ->camera is ready for next capture ->photo saved in galleryThe following chart is a rough description of processes when user takes a photo. If a smartphone camera has good performance, the time between shutter press and ready for next capture should be very very shot. Put in another way, you capture what you see, you capture the exact moment you want.

Lets explore the processes in more detail.What impact the camera performance?Latency has a lot impact!

Those latency in the chart decides how fast you can get a photo.Camera off VF(viewfinder) ON / Launch Time: This is the time between you open camera app and you see object in viewfinder. Sometimes this is called cold start time.

This metrics is important. For example, if you want to capture an important moment, you want your camera opens immediately. You dont want your camera takes 10 mins to open.

Samsung claims that its camera can be brought up to live within 0.7 seconds under various scenarios. Apple also does a good job on this.

This metric is decided by both hardware and software. Hardware platform decides the upper limit of how fast you can open camera, and software tuning decides the actually how close you can reach that limit. How can you minimize this time?

One way is to use Apples method. Make camera ready as possible as you can. When you launch Apples camera from lock screen, the camera is ready before you fully opens the camera app.

Viewfinder Latency: Its the latency between real objects and object seen on the display. If you move camera, particularly for low end phone camera, you would find that preview screen feels laggy. You can watch these two videos to understand what is viewfinder latency.

This is also sometimes called display/screen lag.Shutter Lag:Shutter lag is the delay between triggering the shutter and when the photograph is actually recorded. This is a common problem in the photography of fast-moving objects or people in motion.

The term narrowly refers only to shutter effects, but more broadly refers to all lag between when the shutter button is pressed and when the photo is taken, including metering and focus lag.Shutter lag - WikipediaIn photography, shutter lag is the delay between triggering the shutter and when the photograph is actually recordeden.wikipedia.

orgThere are a few components in shutter lag. AF Latency. For DSLR, if you half press the shutter, camera will try to focus.

This AF lock down time is AF latency. PDAF and ToF(time of light) are used on smartphone to reduce this lag.Shutter Release Lag.

This is the lag between shuttle is fully pressed and shuttle is closed/sensor read. Where there is a lag here? The preview photo is usually different from the actually photo taken by camera.

So when shutter is fully pressed, camera needs to re-configure ISP, sensor, or even exposure, white balance. This lag largely determines what you actually see and what you actually get. Nokia and Apple do a very good job in controlling this lag as short as 200 ms.

However, many Android smartphone doesnt control this lag well, so comes Zero shutter lag technology the camera continuously captures full-resolution images into a ring buffer, and the app goes back in the frame buffer to find the image that corresponds to when you pressed the shutter. Using zero shutter lag, preview and final photo are the same resolution. Using zero shutter lag, not only camera can capture the moment you want, but also can catch the moment before or after you press the shutter.

Therefore, software can even go beyond that and choose the best photo(by various criteria: most crisp, most clear, most focus, biggest smile in the picture, etc) from the ring buffer.The downside of ZSL is power consumption and noise in low light performance. But overall, ZSL improves user experience dramatically.

Shot to Save Latency / Shot to Shot Latency: These are easy to understand terms.In the next post, I will address the IQ(image quality) / Photo quality topic.