What Is Image Quality?

Image quality refers to people's subjective evaluation of the visual perception of an image. Generally speaking, image quality refers to the degree of error in the human visual system caused by the measured image (that is, the target image) relative to the standard image (that is, the original image). Image quality can be further divided into image fidelity and image intelligibility. Image fidelity describes the degree of deviation between the processed image and the original image; and image intelligibility indicates the degree to which a person or machine can extract relevant feature information from the image.

Subjective evaluation usually considers image quality to be measured

Objective evaluation refers to digitizing the test and calculating the results by machine algorithms. Internationally, Imatest and DxO Analyzer are relatively well-known objective evaluation software systems for image quality. Imatest and DxO Analyzer have similarities and differences. They both separate the factors that affect image quality, test each factor separately, and draw conclusions from software analysis. You can see the performance in various aspects very intuitively.

The objective evaluation of image quality is to establish a mathematical model based on the subjective visual system of the human eye, and calculate the image quality through a specific formula. Compared with subjective evaluation, objective evaluation has the characteristics of batch processing and reproducible results, and there will be no deviation due to artificial reasons.

Generally speaking, the objective evaluation of image quality is divided into nine evaluation items, exposure, sharpness, color, texture, noise, anti-shake, flash, focus and artifacts. Each evaluation item is often divided into several small evaluation items. For artifacts, you need to test items such as sharpening, distortion, and vignetting. By testing these items, through scientific calculations, you can very intuitively see what is lacking in various aspects of the performance of the image.

Imatest

Imatest is an image quality evaluation software system owned by Imatest in the United States. The test items include lens resolution test (SFR-MTF), chromatic aberration, color reproduction, color space, and so on. ^[2]

DxO Analyzer

DxO Analyzer is an image quality evaluation software system owned by French DxO company. The test items are similar to imatest. The DxO system can test not only lenses, sensors / ISP / video, but even multi-array cameras. ^[3]