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3.3 Gabor Patches

3.3 Gabor Patches. Dino, Natalie, Maggi , Jessica, Sarah. Sine Wave Grating.

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3.3 Gabor Patches

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  1. 3.3Gabor Patches Dino, Natalie, Maggi, Jessica, Sarah

  2. Sine Wave Grating • A sine wave grating is an image in which light intensity alternates between its brightest and darkest values according to a sine function. The bottom image illustrates a sine wave function, and below you see this function superimposed on the Gabor patch. As you can see, the intensity cycles from its brightest value (white in a high-contrast grating) through a series of intermediate grays, to its darkest value (black in a high-contrast grating), and then back to white again.

  3. Gaussian Window • Sharp edges are formed where the grating meets the background, and in an experiment, these sharp edges could “confuse” a neuron. The edges can be eliminated by multiplying the grating by a “Gaussian window,” which causes the grating to blend in with the background. The Gaussian function is also known as the “normal curve” or the “bell curve”. • You will see that the image’s intensity is highest in the middle and decreases towards the edges, just as the Gaussian function does.

  4. Spatial Frequency • One important property of a Gabor patch is the spatial frequency of its sine wave grating. Spatial frequency is usually measured in cycles per degree: the number of times the sine wave repeats in one degree of visual angle. The image at right illustrates a cycle, and above, two cycles of the grating are highlighted in green. Remember that visual angle is determined by the size of an object and the distance of the object from your eye.

  5. Contrast • The contrast of a Gabor patch’s sine wave grating refers to the intensity difference between the lightest and darkest portions of the patch, as illustrated in the image at right. In a high contrast patch, the lightest regions of the image are white and the darkest regions are black. In a low contrast patch, the lightest regions are light gray and the darkest regions are dark gray.

  6. Phase • The phase of a Gabor patch refers to the relative position, or shift, of the sine wave from left to right. The image at right illustrates the phases of a sine wave, from 0 degrees through 90, 180, 270, and back to 0 degrees.

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