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

To understand how different spatial frequencies contribute to the overall perceived contrast of complex, broadband photographic images, we adapted the classification image paradigm. Using natural images as stimuli, we randomly varied relative contrast amplitude at different spatial frequencies and had human subjects determine which images had higher contrast. Then, we determined how the random variations corresponded with the human judgments. We found that the overall contrast of an image is disproportionately determined by how much contrast is between 1 and 6 c/°, around the peak of the contrast sensitivity function (CSF). We then employed the basic components of contrast psychophysics modeling to show that the CSF alone is not enough to account for our results and that an increase in gain control strength toward low spatial frequencies is necessary. One important consequence of this is that contrast constancy, the apparent independence of suprathreshold perceived contrast and spatial frequency, will not hold during viewing of natural images. We also found that images with darker low-luminance regions tended to be judged as having higher overall contrast, which we interpret as the consequence of darker local backgrounds resulting in higher band-limited contrast response in the visual system.

/pdf/perceived-contrast-in-complex-images-51ti0zx09y.pdf

Perceived contrast in complex images

Computerized image processing was used to analyze color fundus photographs of 11 patients (22 eyes) with macular drusen who were followed for more than 2 years (mean follow-up, 4.7 years). Significant changes over time (more than +/- 20% of baseline area) were measured in the surface area of macular drusen in 18 of 22 (82%) eyes. An increase in the drusen area was associated significantly with eyes with mostly hard drusen and an initially smaller drusen area; but a decrease was associated with eyes with mostly soft drusen and an initially larger drusen area (P less than 0.01). The mean absolute rate of change in the drusen area was more than twice as great in eyes with mostly soft drusen compared with those with mostly hard drusen (P less than 0.05). All eye pairs studied showed a concomitant increase or decrease in the drusen area.

Image analysis of changes in drusen area.

Apparatus and methods for converting continuous grey tone images into high resolution halftone images utilize an iterative, multi-level, multi-resolution error convergence process. The continuous grey tone image is first binarized. At each level of the process, the binarized image is compared with the grey tone image over a larger window of pixels. Within each window, selected binarized image pixels are tested for possible change in binary assignment. The binary assignment of a given test pixel is changed if the change would result in a lower average error over the entire window. By varying the selection of test pixels, the process can provide clustered dot patterns and dithering.

Halftone imaging method and apparatus utilizing pyramidol error convergence

It is assumed that most people are bothered by blur. However, some may tolerate higher levels of blur than others, such as those with reduced vision1 and, perhaps, older individuals2 (Kline DW, et al. IOVS 2006;47:ARVO E-Abstract 1203). A common clinical observation is that patients exhibit various levels of tolerance of degraded image quality induced by vision corrective devices. We investigated whether these individual differences in tolerance of blur are related to personality.

In the late 1940s it was noted that personality factors may be implicated when large individual differences in the results of psychophysical measurements are observed.3,4 Responses were seen to reflect the interplay between perception and individual cognitive and motivational characteristics. More generally, it was believed that individual differences in personality characteristics could influence perceptions of the social and physical environment.5–7 Contemporary personality research has demonstrated that personality traits exhibit both behavioral and perceptual properties. For example, across several studies, hostile individuals not only exhibited anger and aggressive behavior, but they also perceived ambiguous situations and random individuals much more negatively than did less hostile individuals.8,9

Despite the long-held theoretical supposition that personality and perception are meaningfully related, there is a paucity of research on the relationship between personality and visual perception. Over 40 years ago, it was proposed that personality traits correlate with refractive errors.10 Since then, several research groups have investigated this association with inconclusive results.11–16 Other possible relationships between personality and vision that have been investigated include choice of refractive correction,17–21 keratoconus,22–25 strabismus,26 binocular rivalry,27 eye movements,28–30 and visual stress.31 However, we know of no studies of the association of personality and the perception, or tolerance, of blur.

Individuals with presbyopia who wear progressive-addition lenses report limits of clear and comfortable vision beyond those expected from blur-detection thresholds,32 suggesting tolerance of the induced blur. Recently, Atchison et al.33 and Ciuffreda et al.34 proposed new operational definitions of perception of blur, ranging from least (just-noticeable33 or detectable34 blur, which is equivalent to depth of focus35,36) to unacceptable (just-objectionable33 or bothersome34 blur). These measures of unacceptable blur may be more relevant to the evaluation of visual function than are blur-detection thresholds (depth of focus). The linear relationship between blur thresholds and letter sizes33,34 suggests that these judgments were based on the legibility of the letters. The comparable results of the two studies show that such blur tolerance measures can be made reliably in different samples. Neither of those studies reported individual differences in blur tolerance, which would be expected if there is a relationship between personality and blur tolerance. In our study, we measured blur tolerance as the difference between the just-noticeable and the just-objectionable levels of blur.

Blurred vision is a suboptimal condition for humans and may be a sign of maladaptive functioning if allowed to persist. We hypothesized that psychologically high-functioning people do not tolerate blur well, whereas low-functioning people may tolerate blur to their detriment because they lack the psychological resources to positively change their environments.

A Relationship between Tolerance of Blur and Personality

Previous research has established the benefits of image enhancement by spatial filtering for face perception and motion video appreciation among elderly low-vision observers [ Invest. Ophthalmol. Vis. Sci.32, 2337 ( 1991); J. Opt. Soc. Am. A11, 1929 ( 1994)]. It has also been reported that similar enhancement could increase reading speeds by a factor of 2–4 in the same population [cf. Ophthalmology96, 115 ( 1989)]. In our experiments we sought to determine what benefit, if any, was derived from spatial filtering of text for low-vision readers. Results from this series of studies indicate that 66% of patients do increase their reading rate with enhancement, but this increase is small. Change in reading rate with spatial filtering ranged from a 100% decrement to a 125% improvement, with an average 13% improvement. Only 10 of 67 subjects increased their reading rates by 50% or more. The clinical information that we gathered does not allow us to predict accurately which patients will benefit from spatial filtering. On the basis of these findings we conclude that enhancement of text by spatial filtering does not substantially increase reading rates for most low-vision patients.

Eli Peli

Papers

Perceived contrast in complex images

Image analysis of changes in drusen area.

Halftone imaging method and apparatus utilizing pyramidol error convergence

A Relationship between Tolerance of Blur and Personality

Enhancement of text for the visually impaired.