A concept of HDR image capturing from an image sensor device point of view

Abstract

 We can capture good-quality images anywhere as well as anytime. The latest caller phones have high-speed image sensor process units, one speedy processes the captured images to realize a good quality image. I want to list up features of the latest phone cameras.

• HDR(High dynamic range)

• Bokeh, including object detection

• Movie (4K, full HDR)

• Burst mode image capturing

 I focus on the HDR image capture part on this page

 HDR image capturing method has a lengthy historical background, how to control exposure time, shutter speed, etc ... Professional photographers control several parameters such as shutter speed and capture a high-quality and beautiful image but it is very difficult to do the same thing in the hands of general people.
 To generalize the HDR image capture skill, we need some evolutions of processing and image sensor device.

What is the benefit of the HDR function on images?

 Before starting, I think that it is very important to understand the benefit of the HDR image-capturing function. This is one of the examples of HDR images. The original image was captured by utilizing the HDR function. So we can enjoy the details from the dark to the bright part in one image.

Fig.1 Original beautiful image 

 I slightly adjusted the exposure by utilizing a tool. The image is an overexposure image. 

Overexposure image

 The darker parts become brighter and get clear however the brighter parts become brighter and white out. the details disappeared.

 The other image is here, I slightly adjusted the exposure to get an underexposure image.

Underexposure image

 The darker parts become darker and some parts blackout, the black-out part details disappeared, however the brighter part details get clear. 

The concept of HDR is to create a good-quality image from dark to bright. The following note describes the device-side approaches.

The basic concept of HDR image processing

 Digital cameras, in general, control exposure time to create HDR images. It means that the camera captures 2 images (Long and short exposure images) as one shot. And, the image processor makes a fusion image by utilizing both images. 
 There are several approaches and device architectures to capture both long- and short-exposure images. I will explain the architectural part.