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Topic: Spatial frequency

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	Nikon MicroscopyU: Modulation Transfer Function
		As the spatial frequency approaches very large values, the square wave response resembles that of a sinusoid, yielding graphs of the contrast transfer function and the modulation transfer function that are virtually identical.
		At low spatial frequencies, image contrast is the highest, but falls to zero as the spatial frequency is increased beyond a certain point (drawn in Figure 2 as a reduction in amplitude produced in the image).
		It is composed of sinusoidal patterns having a spatial frequency range between 0.2 and 80 line pairs per millimeter with a grayscale optical density range varying between 0.2 and 1.2 and an 80 percent modulation of the sine waves.
	www.microscopyu.com /articles/optics/mtfintro.html (4055 words)

	Spatial Frequency
		The unit employed to express spatial frequency is the number of cycles that fall within one degree of visual angle (each cycle is one dark and one light bar).
		However, at intermediate spatial frequencies, the contrast in the image is degraded by the butter on the lens.
		If those objects contain only very low spatial frequencies (very large objects) or only very high spatial frequencies (very small objects or fine details), they will be less visible and their contrast will have to be high in order for those objects to be seen.
	www.psy.vanderbilt.edu /courses/hon185/SpatialFrequency/SpatialFrequency.html (4828 words)

	My Webpage
		Spatial domain filtering is primarily based on the use of convolution masks, and it is relatively easy to understand.
		Frequency domain filtering is based on Fourier transform which mathematically separates an image into its frequency components, then it is possible to enhance or suppress certain frequencies.
		A linear spatial filter is a filter whose output for pixel p is a weighted average of the pixel values located in a particular spatial pattern around p.
	www.science.gmu.edu /~yxing/759_5/project2.html (1957 words)

	Visual Cortex Neurons of Monkeys and Cats: Temporal Dynamics of the Spatial Frequency Response Function -- Frazor et ...
		the latency of the response increases as the spatial frequency
		Spatial frequencies presented to the cell in E were: 0.6, 0.67, 0.8, 1.0, 1.07, 1.20, 1.33, 1.6, 2.0, 2.4, 2.67, and 3.0 cycles/deg.
		3, 4, and 7, this shift in the latency of the response is systematic: as the spatial frequency increases, the latency increases.
	jn.physiology.org /cgi/content/full/91/6/2607 (9250 words)

	[No title] (Site not responding. Last check: 2007-10-09)
		Spatial frequency filtering is currently being used for image enhancement in medical imagery, such as in Positron Emission Tomography (PET) and Magnetic Resonance Imaging (MRI), as an aid to detection of cancerous regions.
		The agility of the TF Spatial Filter of this invention is further improved by providing a variable blurring length, which translates to a control of the cutoff frequencies for the low and high pass filter operation.
		The center frequency of the resulting band pass filter is determined by the spatial decay parameters of the individual filters, and is therefore tunable, by virtue of examples 1-12.
	www.wipo.int /cgi-pct/guest/getbykey5?KEY=99/04438.990128&ELEMENT_SET=DECL (10799 words)

	Digital Filters - Frequency Filters
		All frequency filters can also be implemented in the spatial domain and, if there exists a simple kernel for the desired filter effect, it is computationally less expensive to perform the filtering in the spatial domain.
		The result in the spatial domain is equivalent to that of a smoothing filter; as the blocked high frequencies correspond to sharp intensity changes, i.e.
		To perform the frequency filtering we transform both the image of the house and the mask into the Fourier domain where we multiply the two images with the effect that the frequencies occurring in the mask remain in the output while the others are set to zero.
	homepages.inf.ed.ac.uk /rbf/HIPR2/freqfilt.htm (2854 words)

	Journal of General Psychology: Effects on face recognition of spatial-frequency information contained in inspection and ... (Site not responding. Last check: 2007-10-09)
		His studies led him to the conclusion that portraits filtered to contain a two-octave range of spatial frequencies that centered on 16 cycles/face were the most recognizable.
		Thus, successively higher bands of spatial frequencies were theoretically used to determine the presence and shape of an object, the recognition of face-like characteristics, the identity of the face, details thereof, and so on.
		They found that although the particular spatial frequencies contained in the stimulus faces had some effect on recognition performance, the degree of overlap between learning and test images was much more important.
	www.findarticles.com /p/articles/mi_m2405/is_3_130/ai_107124686 (1400 words)

	Journal of Vision - Spatial frequency dependence in contextual modulation of shape, by Habak, Wilkinson, & Wilson
		Background: Previous work using deformed circular contours (radial frequency (RF) patterns) has shown that contextual interactions exist among such patterns: perceived deformation from circularity of an RF pattern can be influenced by a concentric RF pattern of higher amplitude.
		Methods: Thresholds for detecting deviations from circularity were measured for a target RF pattern with 5 cycles (RF5, radius 1.14 deg, peak spatial frequency 8cpd) when the pattern was shown alone and with a mask.
		Conclusions: Spatial frequency interactions in contextual modulation of perceived deformation from circularity reveal that masking was found up to at least 2 octaves, unlike traditional experiments of V1-dependent masking, and are consistent with an intermediate-level (V4) processing site.
	www.journalofvision.org /4/8/667 (303 words)

	Journal of Vision - Different temporal frequency tunings in different spatial frequency stimuli for depth perception, ... (Site not responding. Last check: 2007-10-09)
		Results: DC curves were similar with the highest contrast sensitivity at about the same disparity for all temporal frequencies for a given spatial frequency.
		The relative shift of the curve, which corresponds to relative contrast sensitivity, showed a bandpass temporal frequency tuning for low spatial frequency and a lowpass temporal frequency tuning for high spatial frequency.
		These results suggest that the channel sensitive to high spatial frequency is sensitive to low temporal frequencies and the channel sensitive to low spatial frequency is sensitive to high temporal frequencies.
	www.journalofvision.org /3/9/459 (356 words)

	MAS450: Calculating spatial frequency (Site not responding. Last check: 2007-10-09)
		Recently in class, we introduced the equation for calculating the local spatial frequency of the interference pattern formed at a point on a two dimensional surface by two rays of light coming from two mutually coherence sources:
		The spatial frequency f is measured in cycles per unit length (or, equivalently, line-pairs per unit length).
		Well, a negative spatial frequency is the essentially the same as a positive spatial frequency; you can in fact consider spatial frequency to be only positive, and the equation above to include an absolute value sign.
	courses.media.mit.edu /2002spring/mas450/reading/other_handouts/spatial_freq (402 words)

	Dynamics of Spatial Frequency Tuning in Macaque V1 -- Bredfeldt and Ringach 22 (5): 1976 -- Journal of Neuroscience
		Spatial frequency tuning in the lateral geniculate nucleus of the thalamus (LGN) and primary visual cortex (V1) differ substantially.
		Spatial frequency selectivity was measured by the "quality factor" of the tuning curve.
		Positive values indicate that the center spatial frequency of response enhancement was higher than the center spatial frequency of suppression.
	www.jneurosci.org /cgi/content/full/22/5/1976 (6429 words)

	Contrast Sensitivity Function
		The spatial resolution of the visual system is usually assessed using a simple measure of static visual acuity.
		Typically, contrast thresholds of this sort are collected using vertically oriented sine-wave gratings varying in spatial frequency from 0.5 (very wide) to 32 (very narrow) cycles per degree of visual angle.
		After you have completed a set of trials at one of the spatial frequencies, the screen will inform you when a new target spatial frequency is being selected.
	www.usd.edu /psyc301/CSFIntro.htm (1033 words)

	AVSP 2003 Abstract: Shiller et al. (Site not responding. Last check: 2007-10-09)
		By placing these two spatial-frequency portions of the image in direct competition with each other, the use of hybrid stimuli allows for the identification of spatial frequency bands that are preferentially processed by the visual system and not merely sufficient for the task.
		In this paper, we have used a similar technique to explore the range of spatial frequencies that are involved in the processing of audio-visual speech.
		We produced dynamic hybrid stimuli in which two video sequences of a talker producing different VCV utterances (such as 'aba' and 'aga') were spatially low- and highpass filtered at a number of cutoff frequencies (ranging from 2.75 to 44 cycles/face) and then combined.
	www.isca-speech.org /archive/avsp03/av03_257.html (398 words)

	Frequency Domain Filtering
		According to discrete sampling theory, the maximum usable frequency is 0.5 cycles per pixel because at least two pixels are required to define the one cycle of the wave.
		This frequency is called the "Nyquist Frequency" (0.5 cycles/pixel) and is the highest frequency (of intensity variation) that can be accurately reproduced in our data.
		If the Nyquest frequency is given in cycles/cm then it will vary for different pixel sizes.
	www.uab.edu /radiography/Nmt422/Frequency_Domain_Filtering.htm (414 words)

	Spatial aliasing various space axes
		The problem of spatial aliasing begins when two circles touch each other, as shown at 20 Hz in Figure 19.
		Another view of the spatial aliasing problem is that steeply dipping waves are suppressed by the geophone group.
		From this standpoint the limit past which spatial aliasing begins should be thought of in terms of angles at which energy is missing from the data.
	sepwww.stanford.edu /public/docs/iei/dspr/paper_html/node29.html (365 words)

	Medcyclopaedia - Spatial frequency
		frequency of a sinusoidal wave in space and by definition the inverse of the wavelength
		and it is important in imaging as in many imaging processes it is useful to decompose the image data using a spatial Fourier transformation FT on the field of view, whose dimensions define the longest "wave length possible.
		Small objects generate high spatial frequencies, while large objects generate low spatial frequencies.
	www.medcyclopaedia.com /library/topics/volume_i/s/SPATIAL_FREQUENCY.aspx (115 words)

	spatial frequency
		As you add the different spatial frequency waves; (a), (b), (c), and (d), they produce a more complex wave pattern.
		and we have neurons that code for different spatial frequency sine waves, this provides a mechanism by which the visual system might process information.
		It is conceivable that our visual system may code spatial frequency features and perform a Fourier analyses on the complex combination of sine waves that makes up our visual world.
	academics.uww.edu /psych/spatialfreq/spatialfreq.htm (275 words)

	Scanners and sharpening: resolution and MTF
		The spatial sensitivity function for sinc(f /dscan) is a rectangle of length 1/dscan (the length of a sensor element with a fill factor of 1).
		The first sensor null (the frequency where a complete cycle of the signal covers one sample, hence must be zero regardless of phase) is twice the Nyquist frequency.
		The true definition of frequency found in communications textbooks is the rate of change of phase of the function h(x).
	www.normankoren.com /Tutorials/MTF2.html (5445 words)

	Binocular interactions in the cat's dorsal lateral geniculate nucleus. I. Spatial-frequency analysis of responses of X, ...
		cells responded to a broader range of spatial frequencies.
		optimal spatial frequency was low (less than or equal to 0.2 c/deg) for
		the optimal spatial frequency, and cells that were excited generally showed
	jn.physiology.org /cgi/content/abstract/62/2/526 (507 words)

	UCI Faculty Profiles: Barbara A. Dosher
		Spatial attention does not alter the spatial frequency selectivity of the perceptual template.
		Spatial attention excludes noise at the target location.
		Characterizing the spatial frequency characteristics of perceptual templates.
	www.faculty.uci.edu /scripts/UCIFacultyProfiles/DetailDept.CFM?ID=2307 (607 words)

	Articles - Transfer function (Site not responding. Last check: 2007-10-09)
		The group delay (i.e., the frequency-dependent amount of delay to the envelope of the sinusoid introduced by the transfer function) is found by taking the radian frequency derivative of the phase shift,
		For example, if a series of alternating fl and white bars is drawn at a specific spatial frequency, when these bars are observed, the image will be somewhat degraded.
		By definition, the modulation transfer function at a given spatial frequency is defined as follows:
	www.zgrey.com /articles/Transfer_function (465 words)

	Robotics Institute: Spatial Frequency
		It preserves the spatial coherence of the image that would otherwise be lost in a full power spectrum of the whole image.
		It is best-suited for phenomena that need to be described in terms of both spatial and frequency coordinates.
		We have developed a mathematical relationship between the frequency shifts and the surface normal.
	www.ri.cmu.edu /projects/project_364_text.html (739 words)

	Perception > Lecture: Spatial Frequency
		A visual scene is composed of low and high spatial frequencies
		CSF may represent neural elements that are detectors of Spatial Frequency
		Result - there is a dip in the CSF to the "fatigued" channel, Ss becomes less sensitive to that frequency - detectors/neurons are "tired" from responding
	luna.cas.usf.edu /~husband/percept/sptialfq.htm (562 words)

	Characterizing Stereo Matching Problems using Local Spatial Frequency (Site not responding. Last check: 2007-10-09)
		The model of local spatial frequency provides a powerful analytical tool for image analysis.
		A simple geometric analysis leads to an elegant solution in the frequency domain which, when applied to our phase-based system, increases the system's maximum matchable surface angle from 30 degrees to over 75 degrees.
		The views and conclusions contained in this document are those of the author and should not be interpreted as necessarily representing official policies or endorsements, either expressed or implied, of the Department of the Army or the United States Government.
	www-2.cs.cmu.edu /~mwm/thesis (490 words)

	Faculty Publications 96
		Katsumi, O., Arai, M., Wajima, R., Denno, S., and Hirose, T.: Spatial frequency sweep pattern reversal VER acuity vs Snellen visual acuity: effect of optical defocus.
		Katsumi, O., Wajima, R., Mehta, M.C., Itabashi, R., Arai, M., Paranhos, F.R.L., and Hirose, T.: Spatial tuning loss of pattern reversal visual evoked response in optic nerve disease.
		Peli, E., Arend, L., and Labianca, A.T.: Contrast perception across changes in luminance and spatial frequency.
	www.theschepens.org /faculty_publications_96.htm (2154 words)

	CUJ > Image Processing, Part 7: Spatial Frequency Filtering (Site not responding. Last check: 2007-10-09)
		The gray level is low at the left edge of the figure, stays constant for a while, then shifts to a higher gray level.
		Figure 2 shows the side view of an image with high spatial frequencies.
		The rate or frequency of change in the space of the image is high, so the image has high spatial frequencies.
	www.cuj.com /documents/s=8138/cuj9210phillip1/phillip1.htm (698 words)

	Peripheral neural representation of the spatial frequency of a grating moving across the monkey's finger pad -- ...
		Peripheral neural representation of the spatial frequency of a grating moving across the monkey's finger pad
		the temporal frequency of the moving grating (stimulus temporal frequency =
		representation of the grating's spatial period (or spatial frequency)
	jp.physoc.org /cgi/content/abstract/309/1/117 (411 words)

	Untitled Document (Site not responding. Last check: 2007-10-09)
		We hope to develop improvements upon this network model and to incorporate additional information arising from the spatial separations of the sensors.
		Sakai K, Finkel LH: Characterization of Spatial Frequency Cues in the Perception of Shape-from-Texture.
		Nafziger JS, Finkel LH, Palmer LA: The effect of Gabor element orientation and spatial frequency bandwidth on contour detection.
	yoda.seas.upenn.edu /finkel/finkel_body.htm (1796 words)

	Robotics Institute: Modeling Foreshortening in Stereo Vision using Local Spatial Frequency
		Clearly this condition is violated by perspective foreshortening.
		A simple geometric analysis leads to an elegant solution in the frequency domain which, when applied to a Gabor filter-based stereo system, increases the system's maximum matchable surface angle from 30 degrees to over 75 degrees.
		Shafer, "Modeling Foreshortening in Stereo Vision using Local Spatial Frequency," Proceedings of the 1995 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS '95), Vol.
	www.ri.cmu.edu /pubs/pub_1772.html (323 words)

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