Softcopy quality ruler method: implementation and validation

Abstract

A softcopy quality ruler method was implemented for the International Imaging Industry Association (I3A) Camera Phone Image Quality (CPIQ) Initiative. This work extends ISO 20462 Part 3 by virtue of creating reference digital images of known subjective image quality, complimenting the hardcopy Standard Reference Stimuli (SRS). The softcopy ruler method was developed using images from a Canon EOS 1Ds Mark II D-SLR digital still camera (DSC) and a point-and-shoot Kodak EasyShare P880 zoom digital camera. Images were viewed on an Apple Cinema HD Display (30" flat panel) at a viewing distance of 34 inches. Ruler images were made for 16 scenes. Thirty ruler images were generated for each scene, representing ISO 20462 Standard Quality Scale (SQS) values of approximately 2 to 31 at an increment of one just noticeable difference (JND) by adjusting the system modulation transfer function (MTF). A Matlab GUI was developed to display the ruler and test images side-by-side with a user-adjustable ruler level controlled by a slider. Two validation studies were performed at Eastman Kodak Company, Vista Point Technology, and Aptina Imaging in which all three companies set up a similar viewing lab to run the softcopy ruler method. The results show that the three sets of data are in reasonable agreement with each other, with the differences within the range expected from observer variability. Compared to previous implementations of the quality ruler, the slider-based user interface allows approximately 2x faster assessments with 20% better precision.

Adapting the ISO 20462 softcopy ruler method for online image quality studies

“…[3] The reference images for a softcopy ruler, and are also calibrated in terms of image quality JNDs, though as secondary Standard Quality Scale (SQS 2 ) JNDs. The softcopy method has the advantage that new scenes can more easily be generated and used as rulers.…”

A case study in identifying acceptable bitrates for human face recognition tasks

“…The consumer DV camcorder is shown to have produced overall higher quality output than the CCTV system. One option to compensate for this difference is to apply a frequency filter, aiming to visually match the frequency response of the DV recorder to that of the CCTV camera [42]. In this case, this option was omitted, since the current rapid development of CCTV system technology will result in CCTV systems producing comparable image quality to that of consumer video systems.…”

Comparing subjective image quality measurement methods for the creation of public databases

“…A JAVA Graphical User Interface was developed compliant to the standard specifications for the softcopy ruler, with the exception that reference and test images were shown on the same display. This choice proved to be appropriate, since the standard update for softcopy rulers [12] adopted this strategy as well.…”

“…The Single Stimulus method [7] and the Quality Ruler method [9,11,12] are selected as representative methodologies, and tested on pictures impaired with Gaussian Blur. Two sets of images impaired with Gaussian Blur are used: a subset of the LIVE dataset for Gaussian Blur (LS), and a set of highly textured images (HTI), spanning roughly the same range of quality (see fig.1).…”