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Camera Optics Trends and Image Signal Processor

In 2014, according to Mary Meeker’s annual Internet Trends report, people uploaded an average of 1.8 billion digital images every single day. Have you ever imagined how digitally these many images have captured and how a digital camera works to capture an image? How can those images turn out so crisp and clear in varied lighting conditions? Let us share the technology of how the digital camera works using an Image Signal Processor (ISP) and enhance the process of image quality.

These are happening with the tuning of Image signal processing methods, which have represented to enable modern imaging experiences.

Digital Cameras manage the effective way of capturing light from the camera sensors and converting it into a nice image using a consigned Image Signal Processing system.

CMOS sensor:

A CMOS sensor is an image sensor type that consists of an array of pixels, each containing a photodetector and active amplifier widely used in digital camera technologies such as cell phones, CCTV, web cameras, etc.

Image sensor: 

A device that captures light when striking the lens of a camera converts it into an electronic signal and then transmits it to an imaging device processor, which transforms the electronic signal into a digital image.

Image signal processing (ISP):

Image Signal Processing is a method to convert an image into digital form by performing operations like demosaicing, noise reduction, auto exposure, autofocus, auto white balance, and image sharpening designed for digital processing and image quality enhancement.

Image Signal Processor

Working Principle of Digital Camera Sensors:

The Digital Camera Sensors work on the following process.

  • When we open the shutter of a camera, it captures the photons and converts them to an electrical signal that the processor in the camera reads and converts as colors.

  • Those photons that can reach near each of the photosites are detected as an electrical signal.

  • These are varying in strength depending upon how many photons are capturing in the cavity.

Image Signal Processor

An Image Signal Processor is needed to transform a RAW image from a sensor and convert it into a high-quality image.

An ISP is a resolute processor that uses the raw data from a camera sensor and converts it into a workable image.

We can find several variances between the features that ISP does.

But this ISP controller converts the Bayer data into a workable image array. ISP usually onboard SoC, sometimes discrete.

The Roles of Image Signal Processor

  • Demosaicing – Sensor only senses photons, needs Bayer color filter atop sensor to determine color. RGBG / GRGB, interpolate to RGB for each pixel.

  • 3A – Autofocus, Auto Exposure, Auto white balance

  • Correction for lens imperfections – Lens shading, geometry/distortion, vignetting, try to fix image

  • Noise reduction, filtering, HDR, cleaning up, JPEG

  • It has used for controlling the CMOS or assembling focuses.

As the smartphone evolves from being a camera of use to the primary imaging device for most people, having robust controls for when ISP and auto-exposure functionalities fail will become more valuable. Right now, camera UI and UX are rapidly changing from generation to generation, with more toggles.

The Image Signal Processor (ISP) component processes Bayer images to YUV formatted images. It uses configurable ISP hardware and supports the following processing operations.

  • Spatially varying noise filtering
  • Areal Processor (AP)
  • Demosaicer (DM)
  • Stuck at Pixel Outlier Removal (SAPOR)
  • Bad pixel replacement
  • Color Artifact Reduction (CAR)
  • Edge enhancement (EE)
  • General Pixel Processor (GPP)
  • Transfer functions
  • Local Average and Clip (LAC)
  • Histogram statistics
  • Affine transform
  • Down scalar (DS)
  • Flicker band detection (FB)
  • Auto White Balance (AWB) Gains and black level offset
  • Bezier lens shading (LS)

Image Signal Processor

June 10, 2021

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