Computing dynamic range of high dynamic range (HDR) content is an important procedure when selecting the test material, designing and validating algorithms, or analyzing aesthetic attributes of HDR content. It can be computed on a pixel-based level, measured through subjective tests or predicted using a mathematical model. However, all these methods have certain limitations. This paper investigates whether dynamic range of modeled images with no semantic information, but with the same first order statistics as the original, natural content, is perceived the same as for the corresponding natural images. If so, it would be possible to improve the perceived dynamic range (PDR) predictor model by using additional objective metrics, more suitable for such synthetic content. Within the subjective study, three experiments were conducted with 43 participants. The results show significant correlation between the mean opinion scores for the two image groups. Nevertheless, natural images still seem to provide better cues for evaluation of PDR.
When evaluating camera systems for their noise performance, uniform patches in the object space are used. This is required as the measurement is based on the assumption that any variation of the digital values can be considered as noise. In presence of adaptive noise removal, this method can lead to misleading results as it is relatively easy for algorithms to smooth uniform areas of an image. In this paper, we evaluate the possibilities to measure noise on the so called dead leaves pattern, a random pattern of circles with varying diameter and color. As we measure the noise on a non-uniform pattern, we have a better description of the true noise performance and a potentially better correlation to the user experience.
The implementation of automatic, adaptive filters in consumer imaging devices represents challenges to sharpness and resolution evaluation. The widely used e-SFR and other methods based on sine-waves and line targets are not necessarily representative of the capture of natural scene information. The recent dead leaves target is aimed at producing texture-MTFs that describe the capture of image detail under automatic non-linear, and contentaware processes. A newer approach to the texture-MTF measurement that substitutes the dead leaves target with pictorial images is presented in this paper. The aim of the proposed method is to measure effective-MTFs indicative of system characteristics for given scenes and camera processes. Nine pictorial images, portraying a variety of subjects and textures, were set as targets for a DSLR camera and a high-end smartphone camera. Computed MTFs were found to be congruent with the dead leaves MTF. Scene dependency was reported mainly for the smartphone camera measurements, providing insight into the performance of the content-dependent processes. Results from the DLSR camera images, captured with minimum non-adaptive operations, were reasonably consistent for the majority of the scenes. Based on variations in scene-dependent MTFs, we make recommendations for scene content that is best for texture-MTF analysis.
The dead leaves image model is often used for measurement of the spatial frequency response (SFR) of digital cameras, where response to fine texture is of interest. It has a power spectral density (PSD) similar to natural images and image features of varying sizes, making it useful for measuring the texture-blurring effects of non-linear noise reduction which may not be well analyzed by traditional methods. The standard approach for analyzing images of this model is to compare observed PSDs to the analytically known one. However, recent works have proposed a cross-correlation based approach which promises more robust measurements via full-reference comparison with the known true pattern. A major assumption of this method is that the observed image and reference image can be aligned (registered) with subpixel accuracy. In this paper we study the effects of registration errors on the calculation of texture-based SFR and its derivative metrics (such as MTF50), in order to determine how accurate this registration must be for reliable results. We also propose a change to the dead leaves cross-correlation algorithm, recommending the use of the absolute value of the transfer function rather than its real part. Simulations of registration error on both real and simulated observed images reveal that small amounts of misregistration (as low as 0.15px) can cause large variability in MTF curves derived using the real part of the transfer function, while MTF curves derived from the absolute value are significantly less affected.