1.1.1.0 image.getregion

NRAO Home > CASA > CASA Toolkit Reference Manual

image.getregion - Function

1.1.1 Get pixels or mask from a region-of-interest of the image

Description

This function recovers the image pixel or pixel mask values in the given region-of-interest. Regardless of the shape of the region you have specified, the shape of the pixels and pixelmask arrays must necessarily be the bounding box of the specified region. If the region extends beyond the image, it is truncated.

Recall that the recovered pixel mask will reflect both the pixel mask stored in the image, and the region-of-interest (their masks are ‘anded’) – see the discussion in the introduction about this.

The argument axes can be used to reduce the dimensionality of the output array. It specifies which pixel axes of the image to average the data over. For example, consider a 3-D image. With axes=[0,1] and all other arguments left at their defaults, the result would be a 1-D vector, a profile along the third axis, with the data averaged over the first two axes.

This function differs in three ways from getchunk. First, the region can be much more complex (e.g. a union of polygons) than the simple blc, trc, and inc of getchunk (although such a region can be created of course). Second, it can be used to recover the pixel mask or the pixels. Third, it is less efficient than getchunk for doing the same thing as getchunk. So if you are interested in say, iterating through an image, getting a regular hyper-cube of pixels and doing something with them, then getchunk will be faster. This would be especially noticeable if you iterated line by line through a large image.

Arguments


Inputs
region	Region selection. Default is to use the full image.
	allowed:	any
	Default:	variant
axes	Axes to average over. Default is none.
	allowed:	intArray
	Default:	-1
mask	Mask to use. Default is none.
	allowed:	variant
	Default:
list	List the bounding box to the logger
	allowed:	bool
	Default:	false
dropdeg	Drop degenerate axes
	allowed:	bool
	Default:	false
getmask	Get the pixel mask rather than pixel values
	allowed:	bool
	Default:	false
stretch	Stretch the mask if necessary and possible? Default False
	allowed:	bool
	Default:	false

Returns
variant

Example

Suppose that we have a 3-dimensional image called {\sff cube} and wish
to recover the pixel from a simple regular region.

"""
#
print "\t----\t getregion Ex 1 \t----"
ia.fromshape(’cube’, [64,64,64], overwrite=true)
#r1=rg.box(blc=[10,10,10],trc=[30,40]) # Create region
r1=rg.box([10,10,10],[30,40,40]) # Create region
pixels=ia.getregion(r1)
ia.close()
#
"""

Example

"""
#
print "\t----\t getregion Ex 2 \t----"
ia.fromshape(’cube’, [64,64,64], overwrite=true)
pixels = ia.getregion()
pixelmask = ia.getregion(getmask=True)
#
"""

In this example we recover first the pixels and then the pixel mask.

__________________________________________________________________

[next] [prev] [prev-tail] [front] [up]

More information about CASA may be found at the CASA web page

This code is available under the terms of the GNU General Public Lincense