论文笔记(4):基于learning to rank的盲图像质量评价 dipIQ

dipIQ: Blind Image Quality Assessment by Learning-to-Rank Discriminable Image Pairs

Part 1 Introduction

Definition: 盲图像质量评价(Blind Image Quality Assessment)也叫做无参考图像质量评价(NR-IQA)的目的是对于给定的一幅图像,不使用Ground Truth(GT)图像得到其评价分数。
classic method & Problem:

  1. 对于大样本集,通过人工标注得到图像主观分数需要花费很大的代价
  2. 例如TID2013数据集中,使用25GT图像退化得到3000幅图像,这和真实的图像分布相差很大
  3. 由于传统的方法是直接估计图像质量分数的,所以在图像质量分数的顺序上可能会有较大的误差。

Observation & Motivation: 通过对图像进行不同程度的退化,能够得到不同质量的图像,即quality-discriminable image
pairs (DIP)。
Paper method:

使用不同等级的退化因子对GT图像进行退化得到大量的ranked images.
使用ranked images 训练双生网络,得到ranking score.
将在ranked images上训练好的网络在具有label的样本集上进行fine-tune.

Blind image quality assessment (BIQA) aims to predict perceptual image quality scores without access to reference images. State-of-the-art BIQA methods typically require subjects to score a large number of images to train a robust model. However, the acquisition of image quality scores has several limitations: 1) scores are not precise, because subjects are usually uncertain about which score most precisely represents the perceptual quality of a given image; 2) subjective judgments of quality may be biased by image content; 3) the quality scales between different distortion categories are inconsistent, because images corrupted by different types of distortion are evaluated independently in subjective experiments; and 4) it is challenging to obtain a large scale database, or to extend existing databases, because of the inconvenience of collecting sufficient images associated with different kinds of distortion that have diverse levels of degradation, training the subjects, conducting subjective experiments, and realigning human quality evaluations. To combat these limitations, this paper explores and exploits preference image pairs (PIPs) such as “the quality of image Ia is better than that of image Ib” for training a robust BIQA model. The preference label, representing the relative quality of two images, is generally precise and consistent, and is not sensitive to image content, distortion type, or subject identity; such PIPs can be generated at very low cost. The proposed BIQA method is one of learning to rank. We first formulate the problem of learning the mapping from the image features to the preference label as one of classification. In particular, we investigate the utilization of a multiple kernel learning algorithm based on group lasso (MKLGL) to provide a solution. A simple but effective strategy to estimate perceptual image quality scores is then presented. Experiments show that the proposed BIQA method is highly effective and achieves comparable performance to state-of-the-art BIQA algorithms. Moreover, the proposed method can be easily extended to new distortion categories.
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