Recently, ISO standard 15739:2013 revealed the first official visual noise metrics. Until now, signal to noise ratio (SNR) has been used the most as the noise measurement metric for digital cameras, but according to several research studies it does not represent the visual perception of noise included in images. This article investigates the differences between SNR based noise measurements and visual noise measurements when real mobile phone cameras are measured. The work contains the following tasks. Firstly, the improvements between old and new standards are detailed. Secondly, the noise measurements are executed, testing 20 mobile phones using three different light environments. Finally, the results are compared between different noise measurement algorithms and conclusions are drawn. The result of this work gives detailed noise measurement results for mobile phone camera systems on the market. Total and visual noise metrics are measured, also corresponding ISO speed and exposure parameters are stored and correlations between noise levels and parameters are calculated. The differences between noise metrics are summarized and perceptual inspection is made of the images which have clear differences between total and visual noise.
The exact and direct measurement of the muscle activity in the human body is important for the diagnosis of diseases and for the performance measurement of athletes. In particular, the detection of muscle trembling (so-called tremor) under a certain load could be an accurate measure of the progression of diseases or of the muscle’s capability. Until now mostly invasive or contact-based measurement principles have been used for this application. The authors show the development of a setup for an optical measurement of muscle activity which is proven to be capable of measuring fine frequency and amplitude differences of oscillating surfaces in technical and medical applications. Furthermore, the authors show the measurement performance of their method in comparison to an established method. The authors can prove that their method has good applicability for measuring the amplitude and frequency of the tremor remotely and that the results are consistent with mechanomyographic measurements of the tremor.
In this article, the specular reflection phenomenon is analyzed by the concept of the point spread function (PSF). The conventional PSF, which is a sharpness criterion, is used for the transfer function in image science. In general, print (an ink image on paper) is observed as diffuse reflection light, and the light source image, i.e., gloss, is observed as specular reflection. We first introduce the point spread function of specular reflection (SR-PSF). A measurement principle for the SR-PSF is proposed, and a measurement apparatus for the SR-PSF is developed by using a collimator optical system. The experimental results show that the measured SR-PSF works as a transfer function for a specular reflection image. Each detected position is in agreement with the angle of reflected light. The apparatus works as a goniophotometer within a narrow solid angle. The relation between the SR-PSF and the specular reflection angle distribution is discussed in terms of surface geometry. It is concluded that the measured data are the SR-PSF and they have a gonio-reflectance distribution. The reflection angle is caused by the surface normal, and the surface normal distribution can be calculated from the gonio-reflectance distribution by using the mathematical model. We plan to apply our proposed principle to the development of an evaluation technique for the visual gloss. In addition, the high-resolution goniophotometer can be further developed by this measuring technique.
Mapping of the potentially high dynamic range (HDR) of real-world luminance to the low dynamic range (LDR) of photographic devices is one of the classic photographic tasks. Therefore, color compression or color rendering methods have been proposed and described in many works over the past five decades. However, there are well-known problems associated with these methods.
Accordingly, this article presents a color rendering method that is a combination of tone mapping and chromatic adaptation in order to avoid color distortion after performing color correction (or rendering). The tone mapping operator produces visibility, and the overall impression of brightness, contrast, and color in a given HDR image when mapped onto a relatively LDR display or printer. In general, modern display devices differ dramatically from HDR images not only in peak luminance, dark luminance, and dynamic range, but also in the chromaticity of the white point. Ideally, the white point, which always represents its non-chromaticity and chromaticity, is equal to, or very close to, that of the equi-energy stimulus. Therefore, the tone mapping resultant image is obtained using chromatic and achromatic colors. Thereafter, the resulting image is processed through the cone response function using the modified surround luminance factor, and emphasis is placed on human visual perception. The experimental results show that the proposed method yields better performance in color compression than the conventional method in subjective and quantitative quality, and color reproduction.
A new set of color difference data using complex images was collected including small and large color differences. Using 13 images, 182 test images were generated to have various average lightness, chroma or hue values compared to the original images. Twenty observers estimated the overall color difference between the reference and manipulated images shown on an sRGB monitor with 250 cd/m2 as a peak white in a dark room. The magnitude estimation technique was adopted for the visual assessment. The parametric factors of CMC(l:c), and CIEDE2000(l:c) were optimized using the color difference data set. Results showed that CIEDE2000 performs better than CMC. The best ratio for CMC(l:c) is (4:3), while (3.5:1) is the best for CIEDE2000(l:c) for overall color difference prediction.
Color vision deficiency represents an inability to perceive differences between certain colors that can be distinguished in the case of regular color vision. This article proposes a new daltonization method for re-coloring image segments perceived as confusingly colored by color deficient observers and, thus, to improve their perceived image quality. The idea behind this approach is that only one image color center should be located on one confusion line. If colors of two or more segments lie on the same confusion line, then they should be remapped in a direction perpendicular to the confusion line taking into account the image content—the color distribution of other segments. The method conserves the image naturalness by restricting, for each segment center, an area of admissible remapping. This achieves re-coloring balance where colors are made sufficiently distinguishable from each other, but they do not deviate too much from the original image colors. The proposed re-coloring concept is applicable to all types of dichromacy and anomalous trichromacy with adjustment for their set of confusion lines. The simulation results show that the re-coloring converts an original image to a version with improved color distinction, confirmed by evaluations of eight color deficient users. An intentionally chosen example demonstrates when and why the proposed method performs better against content-independent methods. Furthermore, results and subjective evaluations indicate that the method provides more natural re-coloring results for anomalous trichromats than in the case of content-dependent methods optimized for dichromats.