Bloch's Law

	Bloch's Law Bloch's law observes that, for brief presentations, the product of luminance (or contrast) and duration at the detection threshold is constant. The law is due to Adolphe-Moise Bloch, who first formulated it in 1885. Derivation Consider that a brief flash of intensity I is presented for a duration t. Bloch's law states that detection occurs if the total luminance energy I \times t exceeds some threshold value K. Formally,I \times t = KHere, K is a constant that can vary with different viewing conditions, observer attributes, and adaptation levels. Early measurements used single, isolated light flashes of varying duration and intensity to determine the boundary at which a viewer first reports seeing the flash. When plotted against detection thresholds, these data typically exhibit a near-constant product of intensity and duration for short intervals. See also Ricco's law Temporal summation Contrast (vision) Contrast is the difference in luminance or color that makes an obje ... [...More Info...] [...Related Items...] OR:* [Wikipedia] [Google] [Baidu]
	Ricco's Law Riccò's law, discovered by astronomer Annibale Riccò, is one of several laws that describe a human's ability to visually detect targets on a uniform background. It says that for visual targets below a certain size, threshold visibility depends on the area of the target, and hence on the total light received. The "certain size" (called the "critical visual angle"), is small in daylight conditions, larger in low light levels. The law is of special significance in visual astronomy, since it concerns the ability to distinguish between faint point sources (e.g. stars) and small, faint extended objects (Deep-sky object, "DSOs"). Derivation Suppose that an achromatic target of angular area A is viewed against a uniform background luminance B (e.g. a disc of white light is projected on a white screen, or a nebula is seen through a telescope). For the target to be visible at all, there must be sufficient luminance Contrast (vision), contrast; i.e. the target must be brighter (or darker) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Temporal Summation Summation, which includes both spatial summation and temporal summation, is the process that determines whether or not an action potential will be generated by the combined effects of excitatory and inhibitory signals, both from multiple simultaneous inputs (spatial summation), and from repeated inputs (temporal summation). Depending on the sum total of many individual inputs, summation may or may not reach the threshold voltage to trigger an action potential. Neurotransmitters released from the terminals of a presynaptic neuron fall under one of two categories, depending on the ion channels gated or modulated by the neurotransmitter receptor. Excitatory neurotransmitters produce depolarization of the postsynaptic cell, whereas the hyperpolarization produced by an inhibitory neurotransmitter will mitigate the effects of an excitatory neurotransmitter. This depolarization is called an EPSP, or an excitatory postsynaptic potential, and the hyperpolarization is called an IPSP, or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Contrast (vision) Contrast is the difference in luminance or color that makes an object (or its representation in an image or display) visible against a background of different luminance or color. The human visual system is more sensitive to contrast than to absolute luminance; thus, we can perceive the world similarly despite significant changes in illumination throughout the day or across different locations. The maximum contrast of an image is termed the contrast ratio or dynamic range. In images where the contrast ratio approaches the maximum possible for the medium, there is a ''conservation of contrast''. In such cases, increasing contrast in certain parts of the image will necessarily result in a decrease in contrast elsewhere. Brightening an image increases contrast in darker areas but decreases it in brighter areas; conversely, darkening the image will have the opposite effect. Bleach bypass reduces contrast in the darkest and brightest parts of an image while enhancing luminance contr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]