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SGI Developer Toolbox 6.1
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SGI Developer Toolbox 6.1 - Disc 4.iso
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pixtran.hlp
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@C1@c@b@_ Pixel Transformation
Perform arbitrary 1-to-1 pixel transformations. The transformation
can be applied to RGB separately or simultaneously and to the entire
image or a rectangular region of it.
The transformation is defined by three (representing RGB) XY plots,
whose horizontal axes are the input pixel values and the vertical axes
are the output pixel values.
@b Interaction
A transformation is altered by dragging the movable control points
shown as little squares on the transformation function plots.
The four buttons on the top right corner of the panel control to
which color channel the current transformation applies. Immediately
below is a counter that controls the number of movable points on the
transformation plots.
Following buttons and shortcuts are available
@f Invert
Replace every pixel by its compliments, i.e., photo-inversion.
@f Steps
Primitive quantization by clustering pixels.
@f Band
Set alternating clusters of pixels to black.
@f Threshold
Set the transformation to a 2-level step function.
@f Upshift
Shift the current component(s) up one bit. No check for overflow is made.
@f Dnshift
Shift the current component(s) down one bit.
@f Reset
Set the current transformation to null, i.e., output(x) = input(x);
@f Gamma
Gamma correction with allowable gamma range of 0.001 to 10.00.
@f Brightness
Brightness can be changed either by absolute value (p += delta) or by
a percentage (p *= (1.0 + delta)). To switch, click the mouse on the
text "brightness".
@f Constrast
Make dark pixel darker and bright pixels brighter
@f Swap
Swap two pixel values, e.g., black and white
@f Replace
Replace one pixel value with another
@f Apply
Perform the current transformation and display the resulting image.
@f Undo
Undo last transformation. Only one undo is allowed.
@f Done
Exit color editing mode.
@b Math Expressions
Arbitrary math expression can be entered by clicking on the MathExp
button. The built-in parser recognizes +-*/ and ^ (or **) operators
and some of the standard functions from libm.a.
The math expression must be entered with x as the variable name,
such as (x+1)^2/4 (or if you like, y = x^2). The parser will use the
current x values ([0,1] inclusive) to evaluate the expression.
@f built-in functions
@f cos, sin, acos, asin, tan, atan, deg, rad
@f sqrt, cbrt, abs, exp, log, log10
@s@b Note
1. In choosing the target or new pixel values in Swap & Change,
it is a good idea to use the Pixel-picking features of the
color selection (CNTL + leftmouse) because pixels might not
be what they appear to be (e.g., (1,0,0) and (0,0,0) look the
same to the eye).
2. The transformation is additive, i.e., the transformation always
applies to the current image.
3. A bluish glass can be achieved by using a function that
shifts red and green intensities down 2bits, or simple use the blue
intensities alone. Similar tricks can be used to achieve greenish
glass etc.