average light intensity from sine equation

Here, luminance contrast is used as an example, but the formulas can also be applied to other physical quantities. Various definitions of contrast are used in different situations. It complicates the solution of many applied problems and makes it difficult to compare the results published by different authors.' Travnikova laments, 'Such a multiplicity of notions of contrast is extremely inconvenient. There are many possible definitions of contrast. Quantifications An image of the Notre Dame cathedral as seen from the Eiffel Tower The same image, with added global contrast, and local contrast ( acutance) increased through unsharp maskingĪ photograph of a leaf with several colors-the bottom image has an 11% saturation boost and around 10% increase in contrast. For some screens the angle between the screen surface and the observer's line of sight is also important. įor example, in the case of graphical computer displays, contrast depends on the properties of the picture source or file and the properties of the computer display, including its variable settings. Since white minus blue is red and green, this mixes to become yellow. The yellow is derived from the inhibition of blue on the surroundings by the center.

One experimental phenomenon is the inhibition of blue in the periphery if blue light is displayed against white, leading to a yellow surrounding. A typical retinal ganglion cell's receptive field comprises a central region in which light either excites or inhibits the cell, and a surround region in which light has the opposite effects. The low frequency drop-off is due to lateral inhibition within the retinal ganglion cells. The high-frequency cut-off is also related to the packing density of the retinal photoreceptor cells: a finer matrix can resolve finer gratings. The high-frequency cut-off represents the optical limitations of the visual system's ability to resolve detail and is typically about 60 cyc/deg. This can be observed by changing one's viewing distance from a 'sweep grating' (shown below) showing many bars of a sinusoidal grating that go from high to low contrast along the bars, and go from narrow (high spatial frequency) to wide (low spatial frequency) bars across the width of the grating. Bleach bypass destroys contrast in both the darkest and brightest parts of an image while enhancing luminance contrast in areas of intermediate brightness.Ĭampbell and Robson (1968) showed that the human contrast sensitivity function shows a typical band-pass filter shape peaking at around 4 cycles per degree (cpd or cyc/deg), with sensitivity dropping off either side of the peak. Brightening an image will increase contrast in dark areas but decrease contrast in bright areas, while darkening the image will have the opposite effect. Images with a contrast ratio close to their medium's maximum possible contrast ratio experience a conservation of contrast, wherein any increase in contrast in some parts of the image must necessarily result in a decrease in contrast elsewhere. The maximum contrast of an image is the contrast ratio or dynamic range. The human visual system is more sensitive to contrast than to absolute luminance we can perceive the world similarly regardless of the huge changes in illumination over the day or from place to place. Six renditions of a rocky shore photo with incremental contrast levels, clockwise from bottom left.Ĭontrast is the difference in luminance or colour that makes an object (or its representation in an image or display) visible on a background of different luminance or color. The contrast in the left half of the image is lower than that in the right half. To find the field angle, repeat these steps, but mark the two spots where the beam intensity reaches 10% of the maximum level.For broader coverage of this topic, see Display contrast.This is the 'beam angle,' and describes the angle illuminated brightly by the light source. Use a protractor to measure the angle between your two lines.Walk in the other direction until you find the spot on the opposite side of the beam with 50% maximum illumination.Use a taut string or other straightedge to mark the line from the light source to this point. Staying the same distance from the light source, move the photometer in one direction, until the light intensity drops to 50% of the maximum level.Move it around until you find the spot with the maximum intensity (illuminance).

Hold the photometer directly in the path of the brightest beam.X Research source You can find these yourself using a photometer that measures lux or foot-candles, and with a straightedge and protractor: Flashlights and other devices that emit light in a certain direction can be described using these two additional terms.

Average light intensity from sine equation