by Chris Peterson » Mon Oct 12, 2015 2:02 pm
DavidLeodis wrote:The "luminance" in the explanation is a link to the definition of luminance. I've long assumed that luminance simply meant light that was not a specific colour (such as red, green and blue filters are specific). The definition of luminance does not seem to mean what I thought it meant (not that I really understand the definition :? and a bit :oops: ). I would be grateful if someone could please give an easier to understand definition of what luminance means in astrophotography.
In astrophotography (and imaging in general) "luminance" usually refers to the intensity channel of the data ("intensity" being another word with a technical meaning different from how it is used by imagers). So it is, as you suggest, just the image without color information attached- essentially, what you get if you convert a color image to B&W.
More technically, however, photometricists- people interested in extracting useful information from light, and those concerned with the energy of light, use a somewhat bewildering collection of rigorously defined concepts, including intensity, luminance, luminous intensity, flux, irradiance, and many more. These consider things like the angle of emission, area of collection, variation in energy with wavelength, and other factors that are usually not of concern to imagers.
[quote="DavidLeodis"]The "luminance" in the explanation is a link to the definition of luminance. I've long assumed that luminance simply meant light that was not a specific colour (such as red, green and blue filters are specific). The definition of luminance does not seem to mean what I thought it meant (not that I really understand the definition :? and a bit :oops: ). I would be grateful if someone could please give an easier to understand definition of what luminance means in astrophotography.[/quote]
In astrophotography (and imaging in general) "luminance" usually refers to the intensity channel of the data ("intensity" being another word with a technical meaning different from how it is used by imagers). So it is, as you suggest, just the image without color information attached- essentially, what you get if you convert a color image to B&W.
More technically, however, photometricists- people interested in extracting useful information from light, and those concerned with the energy of light, use a somewhat bewildering collection of rigorously defined concepts, including intensity, luminance, luminous intensity, flux, irradiance, and many more. These consider things like the angle of emission, area of collection, variation in energy with wavelength, and other factors that are usually not of concern to imagers.