Camera Tuning: An introduction to the Image Signal Processor and ISP tuning
What is Image Quality (IQ)?
Video images are typically first captured by a lens and sensor. These raw images could have noise from the environment, poor color, limited lighting and many other issues that impact the image quality. In addition to that the fact that some use-cases may require image tuning for human perception while some others for machine vision.
A quality image does not mean a sharp, bright image with high contrast. Image quality is a critical issue that entails much more than brightness and sharpness. Several factors contribute significantly to the quality of the image a camera delivers. An extensive amount of math and processing goes into the process of converting light from your sensor into a good-looking image.
What is the purpose of camera IQ tuning?
Taking quality images in a variety of lighting conditions is essential, including indoors, in strong sunlight, and indarkness. Videos and images taken in dim lighting can easily lose colors, critical details, and gain image noise. Camera systems consist of many components that work together to produce the final image. Image quality defines how well a camera system performs when reproducing an object/scene. Various characteristics of the camera system like sensor, firmware and lens contribute different elements to the overall quality of an image.
We need IQ tuning in order to achieve the best image/video quality from the camera system, as there are:
Lens distortion, sensor defects, noise, color response
Variations in mechanical, optical systems and electrical characteristics
Measurement criteria including automatic exposure (AE) with brightness and saturation statistics, automatic focus (AF) with contrast statistics, and automatic white balance (AWB) with color statistics
Subjectivity due to individual image quality preferences
Unprocessed images do not accurately depict an actual scene. This is where an ISP job begins to obtain the highest image quality possible.
Image Tuning Terminolgies:
Raw image - An uncompressed version of the image file. Raw files are named so because they are not yet processed while containing all information for image processing.
YUV image: YUV is a color encoding system used as part of a color image pipeline. It encodes a color image, allowing reduced bandwidth for chrominance components.
CMOS sensor is an image sensor type that consists of an array of pixels, each containing a photo detector and active amplifier widely used in digital camera technologies such as cell phones, CCTV, web cameras, etc.
A Bayer pattern is an array for arranging RGB color filters on a square grid of photo sensors. Its particular arrangement of red, blue, and green color filters live above the millions of light-sensitive photosite on the surface of a sensor chip.
Image Sensor - A device that captures light when it strikes the lens of a camera and 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) pipeline - 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.
A distortion occurs when straight lines appear to curve as a result of an aberration. Lenses with extreme wide-angle, telephoto, and zoom angles are most likely to exhibit distortion.
The lower the distortion value the better; however, when it comes to consumer photography, such as camera phones, distortion is generally not a major concern.
Color/White Balance Accuracy - White balance (WB) is the process of removing unrealistic color casts, so that objects which appear white in person are rendered white in your photo. In order to achieve a proper white balance on a camera, it is necessary to take into accouny the "color temperature" of the light source, which is the extent to which white light is warm or cool. Although human eyes are excellent at judging what is white under different light sources, digital cameras often have difficulties with auto white balance (AWB) - resulting in unsightly blue, orange, or green color casts. You may be able to avoid these color casts by understanding digital white balance, which will allow you to improve your images under a wider range of lighting conditions.
Lateral Chromatic Aberration (LCA) - Chromatic aberration is a phenomenon in which light rays passing through a lens focus at different points, depending on their wavelength. There are two types of chromatic aberration: axial chromatic aberration and lateral chromatic aberration.
HDR - Dynamic range is simply the range of the lightest tones to the darkest tones within an image. Put another way — it’s a measure of the light intensities from the highlights to the shadows.
ISP - Images are processed using image signal processors (ISPs) in devices such as smartphones, webcams, digital cameras, and other imaging apparatus. This ISP primary function is to process raw image data and convert it into a high-quality image
Image Quaily Tuning is also known as ISP Tuning or Camera Tuning.
Image Quailty Metrics of interest: exposure, dynamic range, noise, color and white balance accurcy, luminance and color shading, resolution, sharpness, distortion, texture blur, fringing and blooming, blemish, dead pixels, feild of view, etc.
For our image quality tuning services visit our image tuning webpage
Contact us for more information.