Brought to you by Google through its Pixel 2, Pixel 2 XL, Pixel, Pixel XL and the Nexus line of phones. So, what does it do? Can it cure cancer? Nope. Can it help you find true love? Erm, Nope. Can it help you find the release date for Half Life 3? Yes.

But what it is mostly famous for, is its ability to give you the perfect shot in a myriad of different lighting conditions without making any apparent sacrifices . It revolutionized the camera quality in these phones. If the DXO marks for the Pixel or Pixel 2 cameras didn’t make it apparent, then this article will. The change in image quality with HDR+ was especially noticeable in Nexus 5 whose camera was quite awful at the start, but today after the incorporation of this miracle, it can take more than decent shots in varied lighting conditions. Let us take a peek at its working!

Nexus 5: Back from the dead

NOTE : We are using a Nexus 5 to take the test shots so that the difference between shots taken with HDR+ on and HDR+ off is even more visible.

 

Prerequisite Knowledge

Dynamic Range:

WDR represents what happens when HDR mode is on in your camera

It is the difference between the brightest and the darkest detail in a camera. This range is less than that of the human eye and because of this limited range you can have blown out parts in an overexposed photo and black patches in underexposed photos in situations where the range of lighting in photograph is larger than the range that could be covered by camera. When the range of lighting has a large difference between the lightest and darkest part of the scene, it can be be called High Dynamic Range.

ISO:

In a camera the light is sensed by the camera sensor due to the photosensitive excitation of electrons (Laymanspeak: release of electrons due to the light energy received by them) which are then processed to produce the image. The signal sent through these electrons has to be amplified in case more details are required from the shot, which can be done by increasing the ISO (sensitivity) of the camera sensor. However, such amplifications also result in the interference (false signals due to excitation of electrons due to heating up of sensor or other factors) amplification which once it becomes significant enough shows up as random colors in shots. Low ISO values mean less sensitive camera sensor and hence, clearer images as interference isn’t significant enough. Eg: ISO 100 vs ISO 3200.Noise:

The randomly colored grains that appear in your photos if the ISO is too high (In low light situations the camera increases ISO to get more detail out of the light that is coming into the lens).

Shutter speed:

In photography, shutter speed or exposure time is the length of time when the film or digital sensor inside the camera is exposed to light, also when a camera’s shutter is open when taking a photograph. Unwanted blur comes into the picture when shutter speeds are lower than about 1/10th of a second.Exposure:

Exposure is the amount of light drawn in by the camera . An image is overexposed when the brighter areas of the photos lose salient details as determined by the photographer. Underexposed is when the darker parts of image lose details. It is just right when the image has all the salient details as determined by the photographer.Histogram: 

Histograms are a very useful tool that many cameras offer their users to help them get a quick summary of the tonal range present in any given image. It graphs the tones in your image from black (on the left) to white (on the right). The higher the graph at any given point the more pixels of that tone that are present in an image. So a histogram with lots of dark pixels will be skewed to the left and one with lots of lighter tones will be skewed to the right.In the examples given for HDR, if for a given scene, one image has more pixels spread across a greater range of histogram as compared to the other, it has captured more detail. So look out for that.

Clipping in histogram :

When certain details in the lighter or darker regions aren’t captured, they look as if they have been suddenly cut as demonstrated in the histogram example below. This is called clipping. If the number of pixels at the very edges of histogram are large as compared to other parts of the histogram, then the amount of detail cut from the picture is higher. HDR images should have lower clipping. So look out for that as well.

Explanation for HDR mode

One way of resolving the problem of the low Dynamic Range of cameras as compared to human eye is to take multiple images at different exposures –

  1.  One or more photos at exposures lower than what the camera software would have considered appropriate for the scene without HDR mode on.

  2. One or more photos at exposures higher than what the camera software would have considered appropriate for the scene without HDR mode on.   

  3. One or more photos at exposures the camera software would have considered appropriate for the scene without HDR mode on.

Now, combine them after alignment and blending to produce an image which covers a wide range of details .

This whole process is called bracketing.

This is quite effective when the lighting is adequate. Eg: Outdoors in the morning. The trick, however, fails when you are in a dark environment and the shots with lower exposure make the shutter speed extremely slow, even while the ISO is high. Firstly, excessive noise is introduced into the photo. Noise can be somewhat dealt with through the extra image data from the three images. Parts of the long-exposure image are blown out (too bright/overexposed) and parts of the short-exposure image tend to be noisy. This makes alignment hard, leading to ghosts, double images and other artifacts.

Why do Mobile cameras have a special need for HDR+?

The camera on a smartphone has a small lens, meaning that it doesn’t gather much light. If a scene is dimly lit, the resulting photograph will contain image noise. One solution is to lengthen the exposure time – how long the sensor chip collects light. This reduces noise, but since it’s hard to hold a smartphone perfectly steady, long exposures have the unwanted side effect of blurring the shot.HDR+ is AVAILABLE for essential phone but you would have to void your warranty to get it.

Finally…

HDR+ Explained

HDR+ addresses this problem by taking a burst of shots with short exposure times, aligning them algorithmically, and replacing each pixel with the average color at that position across all the shots. Averaging multiple shots reduces noise, and using short exposures reduces blur. HDR+ also begins the alignment process by choosing the sharpest single shot from the burst. Astronomers call this lucky imaging, a technique used to reduce the blurring of images caused by Earth’s shimmering atmosphere.

Another limitation of smartphone cameras is that their sensor chips have small pixels. This limits the camera’s dynamic range for which, as discussed above, traditional HDR mode – with all its annoying imperfections, is used. However, bracketing (done in HDR mode) is not actually necessary; one can use the same exposure time in every shot by just varying the ISO. By using a short exposure, HDR+ avoids blowing out highlights, and by combining enough shots it reduces noise in the shadows. This enables the software to boost the brightness of shadows and since all the shots look similar, alignment is robust; you won’t see ghosts or double images in HDR+ images, as one sometimes sees with other HDR software.

On top of this, HDR+ utilizes RAW images (Laymanspeak: Unprocessed images as captured by the sensor – has a lot of information but isn’t refined) through new camera API (specifically Android’s Camera2 API) it could access in phones(if enabled by the manufacturer) having versions of Android above 5.0 (Lollipop) which further explains its exceptionally better results as compared to the conventional camera photographs.

Examples:

1. The Gate 

a.

bZoomed in picture to see sharpness and noise

2.The Building and the Grey(ish) skies

ab

3. Trashy Hostel Room That Totally Doesn’t Belong to The Author

ab

In all the above examples , is the image taken using HDR+ and it stands out in comparison to image taken without using HDR+ (which is a, for the particularly dull among us) . It has more details as shown by the histogram, lesser noise and greater sharpness relatively speaking.

The Future Beckons

Pixel 2 XL: Did you get the picture?

HDR+, forged by Google using machine learning techniques, AI, professional photographers and the vast quantities of data it has at its disposal, holds a lot of promise for the future. Especially, the fields of AI and Machine Learning are seeing great advancements and with Google having mountains of data to feed them, HDR+ is poised to become something incredible. So, watch this space.

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