Metric Description; brisque: Blind/Referenceless Image Spatial Quality Evaluator (BRISQUE). A BRISQUE model. Image Quality Assessment (IQA) algorithms take an arbitrary image as input and output a quality score as output. There are three types of IQAs: Full-Reference IQA: Here you have a ‘clean’ reference (non-distorted) image to measure the quality of your distorted image. This measure may be used in assessing the quality of an image compression algorithm where we have access to both the original image and its compressed version. Reduced-Reference IQA: Here you don’t have a reference image, but an image having some selective information about it (e.g. watermarked image) to compare and measure the quality of distorted image. Objective Blind or No-Reference IQA: The only input the algorithm gets is the image whose quality you want to measure. This is thus called, No-Reference or Objective-Blind. No-Reference IQA In this post, we will discuss one of the No-Reference IQA Metrics, called Blind/Referenceless Image Spatial Quality Evaluator (BRISQUE). Before we go deeper into the theory, let’s first understand two basic terms: Distorted Image: As the name suggests, a distorted image is a version of the original image that is distorted by blur, noise, watermarking, color transformations, geometric transformations and so on and so forth. Natural Image: An image directly captured by a camera with no post processing is a natural image in our context. Here is an example of natural image and a distorted image. Image Quality Assessment : BRISQUE Kushashwa Ravi Shrimali JUNE 20, 2018 32 COMMENTS How-To Machine Learning Tutorial Photography is the favorite hobby of millions of people around the world. After all, how difficult can it be! In the words of Diane Arbus, a famous American photographer — “Taking pictures is like tiptoeing into the kitchen late at night and stealing Oreo cookies.” Taking a photo is easy, but taking a high-quality photo is hard. It requires good composition and lighting. The right lens and superior equipment can make a big difference. But above all, a high-quality photo requires good taste and judgment. You need an eye of an expert. But is there a mathematical quality measure that captures this human judgment? The answer is both yes and no! There are some measures of quality that are easy for an algorithm to capture. For example, we can look at the information captured by the pixels and flag an image as noisy or blurry. On the other hand, some measures of quality are almost impossible for an algorithm to capture. For example, an algorithm would have a tough time assessing the quality of a picture that requires cultural context. In this post, we will learn about an algorithm for predicting image quality score. Note: This tutorial has been tested on Ubuntu 18.04, 16.04, with Python 3.6.5, Python 2.7 and OpenCV 3.4.1 and 4.0.0-pre versions. What is Image Quality Assessment (IQA)? Image Quality Assessment (IQA) algorithms take an arbitrary image as input and output a quality score as output. There are three types of IQAs: Full-Reference IQA: Here you have a ‘clean’ reference (non-distorted) image to measure the quality of your distorted image. This measure may be used in assessing the quality of an image compression algorithm where we have access to both the original image and its compressed version. Reduced-Reference IQA: Here you don’t have a reference image, but an image having some selective information about it (e.g. watermarked image) to compare and measure the quality of distorted image. Objective Blind or No-Reference IQA: The only input the algorithm gets is the image whose quality you want to measure. This is thus called, No-Reference or Objective-Blind. No-Reference IQA In this post, we will discuss one of the No-Reference IQA Metrics, called Blind/Referenceless Image Spatial Quality Evaluator (BRISQUE). Before we go deeper into the theory, let’s first understand two basic terms: Distorted Image: As the name suggests, a distorted image is a version of the original image that is distorted by blur, noise, watermarking, color transformations, geometric transformations and so on and so forth. types of distortions Fig. 1 Distortions used in TID 2008 Database Natural Image: An image directly captured by a camera with no post processing is a natural image in our context. Here is an example of natural image and a distorted image. collage of natural and distorted Fig. 2 Natural Image (left) and Noisy Image (distorted, right) As you can imagine, it is not always clear-cut whether an image is distorted or it’s natural. For example, when a video is smartly rendered with motion blur, the algorithm may get confused about its quality because of the intentional blur. So one has to use this quality measure in the right context. is trained on a database of images with known distortions, and BRISQUE is limited to evaluating the quality of images with the same type of distortion.
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