REGION_GROW
Syntax | Return Value | Arguments | Keywords | Examples | Version History
The REGION_GROW function performs region growing for a given region within an N-dimensional array by finding all pixels within the array that are connected neighbors to the region pixels and that fall within provided constraints. The constraints are specified either as a threshold range (a minimum and maximum pixel value) or as a multiple of the standard deviation of the region pixel values. If the threshold is used (this is the default), the region is grown to include all connected neighboring pixels that fall within the given threshold range. If the standard deviation multiplier is used, the region is grown to include all connected neighboring pixels that fall within the range of the mean (of the region's pixel values) plus or minus the given multiplier times the sample standard deviation.
Syntax
Result = REGION_GROW(Array, ROIPixels [, /ALL_NEIGHBORS] [, /NAN] [, STDDEV_MULTIPLIER=value | THRESHOLD=[min,max]] )
Return Value
REGION_GROW returns the vector of array indices that represent pixels within the grown region. The grown region will not include pixels at the edges of the input array. If no pixels fall within the grown region, this function will return the value -1.
Arguments
Array
An N-dimensional array of data values. The region will be grown according to the data values within this array.
ROIPixels
A vector of indices into Array that represent the initial region that is to be grown.
Keywords
ALL_NEIGHBORS
Set this keyword to indicate that all adjacent neighbors to a given pixel should be considered during region growing (sometimes known as 8-neighbor searching when the array is two-dimensional). The default is to search only the neighbors that are exactly one unit in distance from the current pixel (sometimes known as 4-neighbor searching when the array is two-dimensional).
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.)
STDDEV_MULTIPLIER
Set this keyword to a scalar value that serves as the multiplier of the sample standard deviation of the original region pixel values. The expanded region includes neighboring pixels that fall within the range of the mean of the region's pixel values plus or minus the given multiplier times the sample standard deviation as follows:
Mean +/- StdDevMultiplier * StdDev
This keyword is mutually exclusive of THRESHOLD. If both keywords are specified, a warning message will be issued and the THRESHOLD value will be used.
THRESHOLD
Set this keyword to a two-element vector, [min,max], of the inclusive range within which the pixel values of the grown region must fall. The default is the range of pixel values within the initial region. This keyword is mutually exclusive of STDDEV_MULTIPLIER. If both keywords are specified, a warning message will be issued and the THRESHOLD value will be used.
Note
If neither keyword is specified, THRESHOLD is used by default. The range of threshold values is based upon the pixel values within the original region and therefore does not have to be provided.
Examples
The following example demonstrates how you can grow a pre-defined region within an image of human red blood cells.
Note
Also see Growing a Region (Image Processing in IDL).
Version History
![; Load an image. fname = FILEPATH('rbcells.jpg', SUBDIR=['examples','data']) READ_JPEG, fname, img imgDims = SIZE(img, /DIMENSIONS) ; Define original region pixels. x = FINDGEN(16*16) MOD 16 + 276. y = LINDGEN(16*16) / 16 + 254. roiPixels = x + y * imgDims[0] ; Grow the region. newROIPixels = REGION_GROW(img, roiPixels) ; Load a grayscale color table. DEVICE, DECOMPOSED = 0 LOADCT, 0 ; Set the topmost color table entry to red. topClr = !D.TABLE_SIZE-1 TVLCT, 255, 0, 0, topClr ; Show the results. tmpImg = BYTSCL(img, TOP=(topClr-1)) tmpImg[roiPixels] = topClr WINDOW, 0, XSIZE=imgDims[0], YSIZE=imgDims[1], $ TITLE='Original Region' TV, tmpImg tmpImg = BYTSCL(img, TOP=(topClr-1)) tmpImg[newROIPixels] = topClr WINDOW, 2, XSIZE=imgDims[0], YSIZE=imgDims[1], $ TITLE='Grown Region' TV, tmpImg](javascript:doIDL("; Load an image.\nfname = FILEPATH('rbcells.jpg', SUBDIR=['examples','data'])\nREAD_JPEG, fname, img\nimgDims = SIZE(img, /DIMENSIONS)\n\n; Define original region pixels.\nx = FINDGEN(16*16) MOD 16 + 276.\ny = LINDGEN(16*16) / 16 + 254.\nroiPixels = x + y * imgDims[0]\n\n; Grow the region.\nnewROIPixels = REGION_GROW(img, roiPixels)\n\n; Load a grayscale color table.\nDEVICE, DECOMPOSED = 0\nLOADCT, 0\n\n; Set the topmost color table entry to red.\ntopClr = !D.TABLE_SIZE-1\nTVLCT, 255, 0, 0, topClr\n\n; Show the results.\ntmpImg = BYTSCL(img, TOP=(topClr-1))\ntmpImg[roiPixels] = topClr\nWINDOW, 0, XSIZE=imgDims[0], YSIZE=imgDims[1], $ \n TITLE='Original Region'\nTV, tmpImg\n\ntmpImg = BYTSCL(img, TOP=(topClr-1))\ntmpImg[newROIPixels] = topClr\nWINDOW, 2, XSIZE=imgDims[0], YSIZE=imgDims[1], $ \n TITLE='Grown Region'\nTV, tmpImg")){kind=link}