Edwin H Land

Bio: Edwin H Land is an academic researcher from Polaroid Corporation. The author has contributed to research in topics: Product (mathematics) & Diffusion (business). The author has an hindex of 31, co-authored 353 publications receiving 10979 citations. Previous affiliations of Edwin H Land include Rowland Institute for Science & Harvard University.

Lightness and Retinex Theory

Abstract: Sensations of color show a strong correlation with reflectance, even though the amount of visible light reaching the eye depends on the product of reflectance and illumination. The visual system must achieve this remarkable result by a scheme that does not measure flux. Such a scheme is described as the basis of retinex theory. This theory assumes that there are three independent cone systems, each starting with a set of receptors peaking, respectively, in the long-, middle-, and short-wavelength regions of the visible spectrum. Each system forms a separate image of the world in terms of lightness that shows a strong correlation with reflectance within its particular band of wavelengths. These images are not mixed, but rather are compared to generate color sensations. The problem then becomes how the lightness of areas in these separate images can be independent of flux. This article describes the mathematics of a lightness scheme that generates lightness numbers, the biologic correlate of reflectance, independent of the flux from objects

An alternative technique for the computation of the designator in the retinex theory of color vision.

Abstract: Accepting the first postulate of the retinex theory of color vision that there are three independent lightness-determining mechanisms (one for long waves, one for middle waves, and one for short waves), each operative with less than a millisecond exposure and each served by its own retinal pigment, a basic task of retinex theory becomes the determination of the nature of these mechanisms. Earlier references proposed several workable algorithms. [Land, E. H. (1959) Proc. Natl. Acad. Sci. USA 45, 115-129; Land, E. H. (1959) Proc. Natl. Acad. Sci. USA 45, 636-644; Land, E. H. (1983) Proc. Natl. Acad. Sci. USA 80, 5163-5169; Land, E. H. & McCann, J. J. (1971) J. Opt. Soc. Am. 61, 1-11; Land, E. H. (1986) Vision Res. 26, 7-21.] The present paper describes a relatively simple alternative technique for the computation of the designator in retinex theory and reports the general operational effectiveness of the new technique, including the competence, not possessed by earlier algorithms, for generating Mach bands.

Recent advances in retinex theory and some implications for cortical computations: color vision and the natural image

Abstract: In the Color Vision Symposium at the Academy in April 1958, we showed a series of experiments which demonstrated that "4whereas in color-mixing theory the wavelengths of the stimuli and the energy content at each wavelength are significant in determining the sense of color . . . in images neither the wavelength of the stimulus nor the energy at each wavelength determines the color. This departure from what we expect on the basis of colorimetry is not a small effect, but is complete . .. .' (1, 2). The initial and most engaging experiment comprised taking two black-and-white photographs of the same scene, one through a red filter and one through a green filter, and projecting these two black-and-white pictures in superposition on the screen to yield a single black-and-white panchromatic image of the scene. When a red filter was placed in the path of the light from the projector that contained the picture taken through a red filter, the whole scene became dramatically colored as if in many respects it were a standard full-color photograph. The first paradox was that the radiation coming to the eye of the observer consisted only of various ratios of red light to white light which should have yielded only a variety of pinks. The second paradox was that the overall ratio of light from the one projector to light from the other projector could be changed markedly without changing the color names of the objects in the colored picture: the colors of the individual objects must be determined by the ratio of red light to white light, but a change in the overall ratio of red light to white light did not change the colors. In light of the understanding which we now have, this simple experiment, which was a shock to the intuitive understanding of all of us, turns out to be the most sophisticated experiment we could have undertaken. For the flavor of the many experiments described at the Symposium, I refer you to the two papers (1, 2) at that time. Here, I want to turn to the quantitative procedures which we now use. We prepared a laboratory display which we dubbed a "Mondrian" (although it actually is closer to a van Doesburg), utilizing about 100 colored papers. A paper of a given color would appear many times in different parts of the display, each time having a different size and shape and each time being surrounded by a different set of other colored papers. One reason for the design was to prohibit the superposition of afterimages of areas onto other areas (3), and another reason for the design was to obviate explanations of results in terms of the size or shape or surrounding of any given paper. The Mondrian is illuminated by using three 35-mm slide projectors with no slides in the slide holder. The output of each projector/illuminator is controlled independently. An interference filter passing long waves is placed in the path of one projector, a middle wave filter, in the path of the second, and a short-wave filter, in the path of the third (Fig. 1). One may think of these as relating roughly to the three visual pigments. A telescopic photometer (Spectra Pritchard photometer, model 1980A), placed roughly where the observers will be, receives and measures radiation from about 1/16th of a square inch on each chosen area of the Mondrian when it is pointed at that area. The instrument is calibrated so that at any wavelength it reports directly in watts per steradian per square meter. Let me call your attention to these four papers: yellow, white, green, and blue. The telescope is pointed at a yellow paper. The short-wave and middle-wave illuminators are turned off, and the whole Mondrian is illuminated with the long-wave illuminator. The output of this projector is then changed until the meter reads exactly "one" (0.1 W per Sr2 per m2). The longwave illuminator is turned off and the middle-wave illuminator is turned on. Its output is adjusted until the meter reads one. This ensures that the amount of middle-wave energy now reaching the meter from that small patch is equal to the amount of long-wave energy. Finally, after the middle-wave illuminator is turned off, the short-wave illuminator is turned on, and its output is set so that the meter (which we must remember is reading the radiation to our eyes) reads one. All three illuminators are now turned on. While looking at the Mondrian as a whole, we note that the yellow paper looks yellow. We now turn our attention to the white paper, pointing the telephotometer at it. We go through the same procedure of illuminating with one illuminator at a time and of setting each illuminator so that the light coming this time from the white paper to the meter, and hence to our eyes, measures one for the long wave and one for the middle wave and one for the short wave. Thus, we have arranged to have coming to our eye from the piece of white paper exactly the same flux-the same wavelength composition, the same energy composition-which a moment earlier we had arranged to have coming to our eye from the piece of yellow paper. The somewhat indigestible question is "what color will the piece of paper be which was white in the Mondrian previously?" Keep in mind that the information now coming to our eye from that piece of paper dictates classically that, if one, one, and one coming to our eye gave yellow, then one, one, and one must again be yellow. This conviction dates back to Newton's proposition V (4):

Shifts in selective visual attention: towards the underlying neural circuitry.

Abstract: Psychophysical and physiological evidence indicates that the visual system of primates and humans has evolved a specialized processing focus moving across the visual scene. This study addresses the question of how simple networks of neuron-like elements can account for a variety of phenomena associated with this shift of selective visual attention. Specifically, we propose the following: (1) A number of elementary features, such as color, orientation, direction of movement, disparity etc. are represented in parallel in different topographical maps, called the early representation. (2) There exists a selective mapping from the early topographic representation into a more central non-topographic representation, such that at any instant the central representation contains the properties of only a single location in the visual scene, the selected location. We suggest that this mapping is the principal expression of early selective visual attention. One function of selective attention is to fuse information from different maps into one coherent whole. (3) Certain selection rules determine which locations will be mapped into the central representation. The major rule, using the conspicuity of locations in the early representation, is implemented using a so-called Winner-Take-All network. Inhibiting the selected location in this network causes an automatic shift towards the next most conspicious location. Additional rules are proximity and similarity preferences. We discuss how these rules can be implemented in neuron-like networks and suggest a possible role for the extensive back-projection from the visual cortex to the LGN.

Lightness and Retinex Theory

Abstract: Sensations of color show a strong correlation with reflectance, even though the amount of visible light reaching the eye depends on the product of reflectance and illumination. The visual system must achieve this remarkable result by a scheme that does not measure flux. Such a scheme is described as the basis of retinex theory. This theory assumes that there are three independent cone systems, each starting with a set of receptors peaking, respectively, in the long-, middle-, and short-wavelength regions of the visible spectrum. Each system forms a separate image of the world in terms of lightness that shows a strong correlation with reflectance within its particular band of wavelengths. These images are not mixed, but rather are compared to generate color sensations. The problem then becomes how the lightness of areas in these separate images can be independent of flux. This article describes the mathematics of a lightness scheme that generates lightness numbers, the biologic correlate of reflectance, independent of the flux from objects

The synaptic organization of the brain

Abstract: Introduction to synaptic circuits, Gordon M.Shepherd and Christof Koch membrane properties and neurotransmitter actions, David A.McCormick peripheral ganglia, Paul R.Adams and Christof Koch spinal cord - ventral horn, Robert E.Burke olfactory bulb, Gordon M.Shepherd, and Charles A.Greer retina, Peter Sterling cerebellum, Rodolfo R.Llinas and Kerry D.Walton thalamus, S.Murray Sherman and Christof Koch basal ganglia, Charles J.Wilson olfactory cortex, Lewis B.Haberly hippocampus, Thomas H.Brown and Anthony M.Zador neocortex, Rodney J.Douglas and Kevan A.C.Martin Gordon M.Shepherd. Appendix: Dendretic electrotonus and synaptic integration.

Poisson image editing

Abstract: Using generic interpolation machinery based on solving Poisson equations, a variety of novel tools are introduced for seamless editing of image regions. The first set of tools permits the seamless importation of both opaque and transparent source image regions into a destination region. The second set is based on similar mathematical ideas and allows the user to modify the appearance of the image seamlessly, within a selected region. These changes can be arranged to affect the texture, the illumination, and the color of objects lying in the region, or to make tileable a rectangular selection.

A multiscale retinex for bridging the gap between color images and the human observation of scenes

Abstract: Direct observation and recorded color images of the same scenes are often strikingly different because human visual perception computes the conscious representation with vivid color and detail in shadows, and with resistance to spectral shifts in the scene illuminant. A computation for color images that approaches fidelity to scene observation must combine dynamic range compression, color consistency-a computational analog for human vision color constancy-and color and lightness tonal rendition. In this paper, we extend a previously designed single-scale center/surround retinex to a multiscale version that achieves simultaneous dynamic range compression/color consistency/lightness rendition. This extension fails to produce good color rendition for a class of images that contain violations of the gray-world assumption implicit to the theoretical foundation of the retinex. Therefore, we define a method of color restoration that corrects for this deficiency at the cost of a modest dilution in color consistency. Extensive testing of the multiscale retinex with color restoration on several test scenes and over a hundred images did not reveal any pathological behaviour.