Registration is a fundamental task in image processing used to match two or more pictures taken, for example, at different times, from different sensors, or from different viewpoints. Virtually all large systems which evaluate images require the registration of images, or a closely related operation, as an intermediate step. Specific examples of systems where image registration is a significant component include matching a target with a real-time image of a scene for target recognition, monitoring global land usage using satellite images, matching stereo images to recover shape for autonomous navigation, and aligning images from different medical modalities for diagnosis.Over the years, a broad range of techniques has been developed for various types of data and problems. These techniques have been independently studied for several different applications, resulting in a large body of research. This paper organizes this material by establishing the relationship between the variations in the images and the type of registration techniques which can most appropriately be applied. Three major types of variations are distinguished. The first type are the variations due to the differences in acquisition which cause the images to be misaligned. To register images, a spatial transformation is found which will remove these variations. The class of transformations which must be searched to find the optimal transformation is determined by knowledge about the variations of this type. The transformation class in turn influences the general technique that should be taken. The second type of variations are those which are also due to differences in acquisition, but cannot be modeled easily such as lighting and atmospheric conditions. This type usually effects intensity values, but they may also be spatial, such as perspective distortions. The third type of variations are differences in the images that are of interest such as object movements, growths, or other scene changes. Variations of the second and third type are not directly removed by registration, but they make registration more difficult since an exact match is no longer possible. In particular, it is critical that variations of the third type are not removed. Knowledge about the characteristics of each type of variation effect the choice of feature space, similarity measure, search space, and search strategy which will make up the final technique. All registration techniques can be viewed as different combinations of these choices. This framework is useful for understanding the merits and relationships between the wide variety of existing techniques and for assisting in the selection of the most suitable technique for a specific problem.

A survey of image registration techniques

Let's read! We will often find out this sentence everywhere. When still being a kid, mom used to order us to always read, so did the teacher. Some books are fully read in a week and we need the obligation to support reading. What about now? Do you still love reading? Is reading only for you who have obligation? Absolutely not! We here offer you a new book enPDFd the perception of the visual world to read.

The Perception of the Visual World. By James J. Gibson. U.S.A.: Houghton Mifflin Company, 1950 (George Allen & Unwin, Ltd., London). Price 35s.

There are declines with age in speed of processing, working memory, inhibitory function, and long-term memory, as well as decreases in brain structure size and white matter integrity. In the face of these decreases, functional imaging studies have demonstrated, somewhat surprisingly, reliable increases in prefrontal activation. To account for these joint phenomena, we propose the scaffolding theory of aging and cognition (STAC). STAC provides an integrative view of the aging mind, suggesting that pervasive increased frontal activation with age is a marker of an adaptive brain that engages in compensatory scaffolding in response to the challenges posed by declining neural structures and function. Scaffolding is a normal process present across the lifespan that involves use and development of complementary, alternative neural circuits to achieve a particular cognitive goal. Scaffolding is protective of cognitive function in the aging brain, and available evidence suggests that the ability to use this mechanism is strengthened by cognitive engagement, exercise, and low levels of default network engagement.

/pdf/the-adaptive-brain-aging-and-neurocognitive-scaffolding-3igyn72710.pdf

The Adaptive Brain: Aging and Neurocognitive Scaffolding

A classic photographic task is the mapping of the potentially high dynamic range of real world luminances to the low dynamic range of the photographic print. This tone reproduction problem is also faced by computer graphics practitioners who map digital images to a low dynamic range print or screen. The work presented in this paper leverages the time-tested techniques of photographic practice to develop a new tone reproduction operator. In particular, we use and extend the techniques developed by Ansel Adams to deal with digital images. The resulting algorithm is simple and produces good results for a wide variety of images.

/pdf/photographic-tone-reproduction-for-digital-images-k89wmpv97f.pdf

Photographic tone reproduction for digital images

Blood vessels usually have poor local contrast, and the application of existing edge detection algorithms yield results which are not satisfactory. An operator for feature extraction based on the optical and spatial properties of objects to be recognized is introduced. The gray-level profile of the cross section of a blood vessel is approximated by a Gaussian-shaped curve. The concept of matched filter detection of signals is used to detect piecewise linear segments of blood vessels in these images. Twelve different templates that are used to search for vessel segments along all possible directions are constructed. Various issues related to the implementation of these matched filters are discussed. The results are compared to those obtained with other methods. >

/pdf/detection-of-blood-vessels-in-retinal-images-using-two-2lxvrugvz5.pdf

Detection of blood vessels in retinal images using two-dimensional matched filters

In a previous study the simulation of image appearance from different distances was shown to be effective1 . The simulated observation distance accurately predicted the distance at which the simulated image could be discriminated from the original image. Due to the 1/f nature of natural images spatial spectra, the individual CSF used was actually tested only at one retinal spatial frequency. To test the CSF relevant for the discrimination task over a wide range of frequencies, the same simulations and testing procedure were applied to 5 contrast versions of the images. The lower contrast images probe the CSF at lower spatial frequencies, while higher contrast images test the CSF value at higher spatial frequencies. Images where individually processed for each of 4 observers using their individual CSF to represent the appearance of the images from 3 distances where they span 1, 2, and 4 deg of visual angle, respectively. Each of the 4 pictures at the 5 contrast levels and the 3 simulated distances was presented 10 times side-by-side with the corresponding original image. Images were observed from 9 different observation distances. Subject task was to determine which of the two was the original, unprocessed image. For each simulated distance the data was use to determine the discrimination distance threshold. Results of testing using simulations calculated with CSFs measured from a 2 m where veridical for the images in the 30 - 100% contrast range. The 10% image was discriminated at distances larger than the simulated distances. The 300% image was discriminated at a shorter distance. A second set CSFs were obtained from a range of observation distances (0.5 m to 8 m), to overcome limitations of the display. These data showed higher sensitivity for low frequencies and lower sensitivity at the higher frequencies as predicted by the simulation testing results. Replication of the simulation experiments with the combined CSFs resulted in a much better prediction of the discrimination distances. Thus, the CSF relevant for the image discrimination task was verified over a wide range of spatial frequencies while further validating the visual model and its use for simulations.

Contrast sensitivity function (CSF) and image discrimination

We report on the development of a realistic dynamic simulation of oncoming headlamp glare in a driving simulator. To our knowledge, no such simulation had been attempted or achieved previously. The simulation is based on superposition of a bright LED display through a beam splitter on the simulator screen and synchronizing the illuminated LED position to the image of the simulated oncoming car. LED brightness is adjusted to result in the level of light that such headlights would cause in the driver’s eyes, enabling the testing of glare effect on drivers of different ages and impact (reduction or increase) of various vision devices.

https://pubs.lib.uiowa.edu/driving/article/28081/galley/136373/download/

Development of a System to Study the Impact of Headlight Glare in a Driving Simulator

Patients with tunnel vision frequently saccade to outside their visual fields in visual search

1 Abstract Purpose: In microperimetry, the locations of visual stimuli are reported on a retinal image. The term microperimetry came to represent retinal perimetry even though perimetry with as small or smaller targets can be performed in standard perimetry. The reason that this terminology was established is the assumption that retinal perimetry provides more accurate placement of targets, in relation to fundus features. This was indeed the case in early scanning laser ophthalmoscopes (SLO) where the imaging laser was also used to create the perimetric stimuli and therefore target position was known exactly. Most microperimeters today use different systems for stimulus presentation and retinal imaging. Reported locations on the retinal image will be incorrect when not spatially aligned. We report generic psychophysical methods for confirming spatial alignment of microperimeters. Methods: Two techniques were developed and evaluated using normally-sighted observers and Nidek MP-1 instruments. (1) The physiological blind spot was identified using small stimuli. The center of the optic disk identified by locating the apparent edge of the disk in the retinal image was compared to the center of the blind spot. (2) Angioscotomata of at least two major retinal vessels with orthogonal orientations were mapped. The locations of those angioscotomata were compared to the locations of the vessels in the retinal image. In addition to these techniques, we compared the locations of the fovea of 16 normally-sighted observers to published SLO-derived normal population data based on optic disk location. The effect of head tilt on computed foveal location was examined. Results: Repeatable spatial alignment errors of 0.5o or more could be found using both techniques. Measurement errors associated with different operators, subjects and images were less than about 0.2o. Differences between our small population sample and previous studies were explained by spatial misalignment. Even small tilts of the head produced apparent changes in foveal location. Discussion: These techniques for assessment of spatial alignment could be applied to any microperimeter. Only microperimeters that image the retina and present stimuli using the same system, as found in some SLOs, are not at risk of spatial misalignment. Mislocalization of the foveal location due to spatial misalignment and head tilt may affect studies of macular lesions such as AMD.

Spatial Alignment of Microperimeters

Purpose Efficacy of current visual prostheses in object recognition is limited. Among various limitations to be addressed, such as low resolution and low dynamic range, here we focus on reducing the impact of background clutter on object recognition. We have proposed the use of motion parallax via head-mounted camera lateral scanning and computationally stabilizing the object of interest (OI) to support neural background decluttering. Simulations in head-mounted displays (HMD), mimicking the proposed effect, were used to test object recognition in normally sighted subjects. Methods Images (24° field of view) were captured from multiple viewpoints and presented at a low resolution (20 × 20). All viewpoints were centered on the OI. Experimental conditions (2 × 3) included clutter (with or without) × head scanning (single viewpoint, 9 coherent viewpoints corresponding to subjects' head positions, and 9 randomly associated viewpoints). Subjects used lateral head movements to view OIs in the HMD. Each object was displayed only once for each subject. Results The median recognition rate without clutter was 40% for all head scanning conditions. Performance with synthetic background clutter dropped to 10% in the static condition, but it was improved to 20% with the coherent and random head scanning (corrected P = 0.005 and P = 0.049, respectively). Conclusions Background decluttering using motion parallax cues but not the coherent multiple views of the OI improved object recognition in low-resolution images. The improvement did not fully eliminate the impact of background. Translational Relevance Motion parallax is an effective but incomplete decluttering solution for object recognition with visual prostheses.

Eli Peli

Papers

Contrast sensitivity function (CSF) and image discrimination

Development of a System to Study the Impact of Headlight Glare in a Driving Simulator

Patients with tunnel vision frequently saccade to outside their visual fields in visual search

Spatial Alignment of Microperimeters

Motion Parallax Improves Object Recognition in the Presence of Clutter in Simulated Prosthetic Vision