DifferenceofGaussians DOG Filter

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Difference-of-Gaussians (DOG) Filter
Cartoon of on-center off-surround
receptive field map
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Simultaneous Brightness Contrast Stimulus
DOG Filter
Convolution Output
Convolution
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Why Darkrooms and Instrument Panels are
Red Refer to the photopic and scotopic spectral
sensitivity functions, above.   Note that
photopic sensitivity is greater than scotopic
sensitivity at wavelengths longer than 555 nm,
and that the difference between scotopic and
photopic sensitivity increases as wavelength
increases.  This is the reason why instrument
panels and darkrooms are typically illuminated at
night by deep red light.  The long wavelength
illumination stimulates the higher-resolution
photopic system, thus enabling the observer to
read the instruments.  At the same time the deep
red light is a poor stimulus for the scotopic
system, so it doesn't disturb the scotopic
system's state of dark adaptation, and therefore
the observer is still dark adapted after reading
the instruments.
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