Point Grey Grasshopper - Saturation; Sharpness; White Balance

Point Grey Research Grasshopper Technical Reference
Camera Operations and Features
Revised 26-Nov-10
Copyright (c) 2010 Point Grey Research Inc.
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Gamma is applied after the analog-to-digital conversion and is controlled using the GAMMA
register 0x818. It can be used to apply a non-linear mapping of the resulting 11-bit image down to
9 bits. By default, Gamma is OFF and has a value of 1.0, which yields a linear response. For
more information regarding the LUT CSR registers, refer to the PGR IEEE-1394 Digital Camera
Register Reference.
L
Due to limitations in the Bayer interpolator, LUT/gamma correction is
unavailable in the following situations:
1. Pixel clock is greater than 50MHz. The pixel clock frequency can be
read from the floating point PIXEL_CLOCK_FREQ register 0x1AF0.
2. Image width or height is greater than 2040 pixels.
3. Image data format is either Y8, Raw8 or Raw16.
4.6.3. Saturation
The Grasshopper supports saturation, which refers to color saturation, as opposed to saturation
of a CCD charge. Saturation is controlled using the SATURATION register 0x814
4.6.4. Sharpness
The Grasshopper supports sharpness, which refers to the filtering of an image to reduce blurring
at image edges. Sharpness is implemented as an average upon a 3x3 block of pixels, and is only
applied to the green component of the Bayer tiled pattern. For sharpness values greather than
1000, the pixel is sharpened; for values less than 1000 it is blurred. When sharpness is in auto
mode, if gain is low, then a small amount of shaping is applied, which increases as gain
decreases. If the gain is high, a small amount of blur is applied, increasing as gain increases.
4.6.5. White Balance
The Grasshopper supports white balance, which is a name given to a system of color correction
to deal with differing lighting conditions. Adjusting the white balance by modifying the relative gain
of R, G and B in an image enables white areas to look "whiter". Taking some subset of the target
image and looking at the relative red to green and blue to green response, the general idea is to
scale the red and blue channels so that the response is 1:1:1. The white balance scheme outlined
in the IIDC specification states that blue and red are adjustable and that green is not. The blue
and red values can be controlled using the WHITE_BALANCE register 0x80C.
The Grasshopper also implements Auto and One_Push white balance. One of the uses of
one_push / auto white balance is to obtain a similar color balance between different cameras that
are slightly different from each other. Theoretically, if different cameras are pointed at the same
scene, using one_push / auto will result in a similar color balance between the cameras.
One_push is similar identical to auto white balance, except One-Push only attempts to
automatically adjust white balance for a set period of time before stopping. The white balance of