Studies on the effect of MegaPixel sensor resolution on displayed image quality and relevant metrics

Chuang Hsin Hung,Sophie Triantaphillidou,Jan Smejkal,Edward W. S. Fry

doi:10.2352/issn.2470-1173.2020.9.iqsp-170

Abstract

This paper investigates camera phone image quality, namely the effect of sensor megapixel (MP) resolution on the perceived quality of images displayed at full size on high-quality desktop displays. For the purpose, we use images from simulated cameras with different sensor MP resolutions. We employ methods recommended in the IEEE 1858 Camera Phone Image Quality (CPIQ) standard, as well as other established psychophysical paradigms, to obtain subjective image quality ratings for systems with varying MP resolution from large numbers of observers. These are subsequently used to validate image quality metrics (IQMs) relating to sharpness and resolution, including those from the CPIQ standard. Further, we define acceptable levels of quality - when changing MP resolution - for mobile phone images in Subjective Quality Scale (SQS) units. Finally, we map SQS levels to categories obtained from star-rating experiments (commonly used to rate consumer experience). Our findings draw a relationship between the MP resolution of the camera sensor and the LCD device. The chosen metrics predict quality accurately, but only the metrics proposed by CPIQ return results in calibrated JNDs in quality. We close by discussing the appropriateness of star-rating experiments for the purpose of measuring subjective image quality and metric validation.

Highlights

According to the Camera Phone Image Quality (CPIQ) working group [1], “consumers most often use the [sensor megapixel] MP count as a way to evaluate the camera quality of their mobile devices, there are many other factors that influence perceived mobile camera image quality”
Given the effect of camera MP count on visual resolution and sharpness, and the camera-processing-display-observer imaging chain, the following questions are considered in this paper: i) what is the effect that increasing MP resolution has on the quality of pictures viewed on common LCD displays? ii) How many pixels are enough for the picture to be deemed by consumers of acceptable displayed quality for camera phone imaging? In this paper we investigated these questions by collecting psychophysical data from images originating from different resolution sensors, using different psychophysical paradigms
This paper investigated how the resolution of phone camera sensors affects the displayed image quality, when images are displayed at full size on quality LCDs

Summary

Introduction

According to the Camera Phone Image Quality (CPIQ) working group [1], “consumers most often use the [sensor megapixel] MP count as a way to evaluate the camera quality of their mobile devices, there are many other factors that influence perceived mobile camera image quality”. It is well established that, increasing camera MP resolution contributes, generally, to sharper displayed images, it is well known to camera experts that optics, other sensor parameters (notably noise) and camera image signal processing (ISP, e.g. denoising, sharpening) affect considerably both resolution and sharpness. It is useful to consider the camera-processingdisplay-observer system in the modeling of image’s resolution and sharpness and to calculate relevant metrics in the spatial frequency domain at the plane of the observer’s eye. Given the effect of camera MP count on visual resolution and sharpness, and the camera-processing-display-observer imaging chain, the following questions are considered in this paper: i) what is the effect that increasing MP resolution has on the quality of pictures viewed on common LCD displays?

Methods

Results

Conclusion