Does your shiny new iPhone often display HDR in-camera and photos? You would have heard this term, ‘HDR’ in Tv advertisements. HDR is a new format and they are getting popular and affordable phones and TVs these days. So, what is HDR on the iPhone? What exactly this HDR do to the images and photos we see.
What is HDR?
As you probably know HDR stands for High dynamic range. This is the new format to display photos and videos in a high dynamic range. The term is currently different for both photos and videos. We will explain it in detail. Before that, Let’s see what is a dynamic range.
Every image you take has a dynamic range. Every film you watch has a dynamic range. Dynamic range is simply the ratio of a bright spot on the image to the darkest part of the image displayed.
Please take a look at this picture. There are brightest spots like sun, rays everywhere in the picture. can you see the darker side of the picture very detailed? Yes. The deals near the dark or also called as ‘shadows details’ are well preserved. We see the highlights detailed like the rays of the sun and not blown out. We also see the textures of the trees. They are not blown out. Thus this image has a very good dynamic range.
Now, look at the same picture below.
Can you spot the difference? Obvious, isn’t it?
You can see that the finer details in the shadow of the tree trunk are gone. The image seems to be darker. The details are less shown. Also note that the blown-out highlight details like the sun, sun rays. It doesn’t have the details as above. That simply means the picture has a less dynamic range. A camera sensor with less dynamic range can take photos with bad shadow details and bad highlights.
Wikipedia says dynamic range as
Here in our context, it is the ratio of the resolving darkest part and the brightest part while the details are preserved.
What is HDR?
Now, you might have guessed what is HDR. Yes, it is ‘high dynamic range.’ But wait. There’s more to it.
HDR in photos and HDR in movies is Different. Therefore, for the question of What is HDR on iPhone, it is a different answer for camera/photos and movies.
What is HDR in equipment?
HDR in any equipment means the ability of it to handle the HDR content. For example, HDR in-camera is that the camera can take still HDR images or videos. HDR in a TV means, it can playback HDR contents on TV. Taking HDR images and watching it on a display is different from Playing back HDR on a TV.
I will explain both with iPhone as an example.
What is HDR on iPhone?
Let’s split the topic into three parts.
- HDR in camera
- HDR in Images
- HDR in video playback.
This way it is less confusing and easier to explain.
What is HDR on iPhone camera
When you open the camera, you might see HDR highlighted. Be it iPhone 8 or iPhone 11, it’s the same. Btw, would you like to read is iPhone 8 worth it? Okay, back to the topic.
You can touch the HDR menu to turn on manually. The world we see is dynamic. We see the bright light and dark shadows. The dynamic range of the human eye is about 20 stops. Yes, Dynamic range is measured in stops. The camera, however, can see about 10 – 14 stops. It means that the camera is limited to capture 10 to 14 times of illumination doubles between the dimmest part in the picture to the brightest part of the picture.
To tell an example, let’s take a candle.
The camera can capture candlelight without an issue. Let’s assume this be stop 1 of dynamic range although, in reality, the readings are different. Anyways, We assume it as the darkest of the image we take. Now, light up another candle and put it along with the fire of the first candle. Now, the flame is twice as bright as the initial candle. It is 2 stops.
Lets do the math
Now for the three-stop dynamic range, we need 2*2 = 4 candles. For 4 stop dynamic range, we need 4*2 = 8 candles. For 5 we need 16 candles. Now imagine 14 stops of dynamic range we would need 16384 candles lighted together. The camera captures all the details of the fire in the big flood of light without blowing out. This is 14 stops of luminosity with respect to 1 candle.
If one more candle is lit, technically, the system will clip and blow out the highlight caused by that candle. It is the same even a million candles are lit, it will clip and blow out all the details.
Every time you alter the aperture, iso, or shutter speed, one double illumination gets affected. If you alter any one of the above ‘+1 stops”, the first candle double becomes irrelevant and ignored. But the sensor considers the next double of 16384 candles ie) 32768 candles.
What your iPhone does is, it take three consecutive photos of different exposures. The camera app then merges it together and give an HDR picture. I will explain it to you clearly. The first picture Blows the highlights but preserving dark shadow details.
Assuming the forest picture above, the first picture taken by the iPhone blows out the sun and sun rays part. But it preserves the deep shadow details of tree trunk and bushes. The next will be a normal picture. In this, The camera misses the shadow details and dark parts. It blows out the highlights like the sun as well but captures the midrange of the image nicely.
In the third photo, the increased exposure darkens the shadows and midrange of images. This is to take the finer details of the highlights like the sun rays. Now, the software takes the shadows of the first picture, mids of the second picture, and the highlight of the third picture for processing. It then stitches them together to make a final picture. This picture Looks incredible with perfect shadow details and highlights. The phone saves it to the photos app.
What is HDR on iPhone: photos
Coming to the next section of what is HDR on iPhone, we are going to see the image application that reproduces the HDR image. Saved photos are in non-HDR format. In fact, they are standard images. The algorithm combines three images into one and saves as a normal jpeg format. So, the photos app or any such app, will have no trouble with decoding and displaying the HDR photo that the iPhone created.
What is HDR on iPhone: videos
This is an entirely different topic compared to HDR in photos. Basically, the cinema-grade camera has a higher dynamic range than the TV we use to watch movies. Hence came the HDR format. The camera captures visuals. Engineers master the visual with HDR in mind. HDR videos have two parts. One is a movie in a normal format. The second one is the HDR metadata.
When you play the movie on a TV with an HDR decoder or a device like an iPhone 11 pro, we can see the pristine video that the camera has captured. Unfortunately, the same video file cannot be used for non-HDR devices.
HDR consist of two important features. Brightness and color space. Engineers master HDR movies at 1000 Nits. What is Nits?
Nit is the measurement of brightness. Normal TVs are of 250 nits. HDR TVs are 500 to even 10,000 nits. 1000 nits is a decent and unofficially a standard value. Your iPhone 11 Pro has a brightness level of 800 nits normally and peaks at 1200 nits. That is a very bright display. Hence, watching HDR content on an iPhone is wonderful.
Remember there’s a second feature of HDR?
The color space
Color space is the number of colors or saturation the screen can display. Normal displays are rec 709 standards. HDR monitors used to process HDR videos are BT 2020 standards. There is a standard between the two. That is DCI p3. Most HDR TVs adhere to this standard. Current iPhones have a 100% DCI p3 compatible display. Thus, videos are vibrant when watched on an iPhone.
Along with higher brightness and larger color space, iPhones 11 pros are great for HDR content consumption.
iPhones can take HDR photos at a fraction of a second is such a great feature. It plays back HDR videos too incredibly well. We now know what is HDR and its implementation on the iPhone. I have always recommended to turn on the HDR feature on your iPhone. Hence you get a great picture every single time you capture the perfect shot. Thanks for reading.
Aju Vignesh Sathiaraj Padma is a mechanical and audio engineer. He is a person who loves technology and things. He is also an audiophile and loves to listen to audio gears. He is an avid writer and loves to blog.