BYTSCL
Syntax | Arguments | Keywords | Examples | Version History | See Also
The BYTSCL function scales all values of Array that lie in the range (Min ≤ x ≤ Max) into the range (0 ≤ x ≤ Top).
- For floating-point input, each value is scaled using the formula (Top + 0.9999) × (x - Min)/(Max - Min).
- For integer input, each value is scaled using the formula (Top + 1) × (x - Min - 1)/(Max - Min).
(See Note on Integer Computation.)
Syntax
Result = BYTSCL( Array [, MAX=value] [, MIN=value] [, /NAN] [, TOP=value] )
Return Value
The returned result has the same structure as the original parameter and is of byte type.
Arguments
Array
The array to be scaled and converted to bytes.
Keywords
MAX
Set this keyword to the maximum value of Array to be considered. If MAX is not provided, Array is searched for its maximum value. All values greater or equal to MAX are set equal to TOP in the result.
Note
The data type of the value specified for MAX should match the data type of the input array. Since MAX is converted to the data type of the input array, specifying mismatched data types may produce undesired results.
MIN
Set this keyword to the minimum value of Array to be considered. If MIN is not provided, Array is searched for its minimum value. All values less than or equal to MIN are set equal to 0 in the result.
Note
The data type of the value specified for MIN should match the data type of the input array. Since MIN is converted to the data type of the input array, specifying mismatched data types may produce undesired results.
NAN
Set this keyword to cause the routine to check for occurrences of the IEEE floating-point values NaN or Infinity in the input data. Elements with the value NaN or Infinity are treated as missing data. (See Special Floating-Point Values (Application Programming) for more information on IEEE floating-point values.)
TOP
Set this keyword to the maximum value of the scaled result. If TOP is not specified, 255 is used. Note that the minimum value of the scaled result is always 0.
Thread Pool Keywords
This routine is written to make use of IDL's thread pool, which can increase execution speed on systems with multiple CPUs. The values stored in the !CPU system variable control whether IDL uses the thread pool for a given computation. In addition, you can use the thread pool keywords TPOOL_MAX_ELTS, TPOOL_MIN_ELTS, and TPOOL_NOTHREAD to override the defaults established by !CPU for a single invocation of this routine. See Thread Pool Keywords for details.
Note on Integer Computation
When scaling integer values, the scaling algorithm is optimized for speed when the range of values (Max - Min) is less than 222. In this case, the actual formula used is:
Scale = (222 × (Top + 1))/(Max - Min)
Result = ((x - Min) × Scale - 1) × 2-22
where all computations are done using integer arithmetic.
Examples
Note
Also see Byte-Scaling (Image Processing in IDL).
BYTSCL is often used to scale images into the appropriate range for 8-bit displays. In the following example, we create a 200x200 image, and then rescale the image pixels from 0 through 255.
Version History
