distmap {EBImage} | R Documentation |
The function performs a distance map transform of binary images. In a distance map each pixel contains the distance from that pixel to the nearest background point.
## S4 method for signature 'Image': distmap(x, t=0.05, exact=FALSE, bg=0.05, ...)
x |
A Grayscale object of Image .
x is considered as a binary image, consisting of 0's for background
and all other values for foreground. |
t |
A numeric value for the background threshold in the range
[0,1) . Pixels with intensity smaller than t are considered
as background. |
bg |
A numeric value for the allowed minimum for the fraction of background pixels in the image. The default and recommended value corresponds to 5% (0.05). See details for more information. |
exact |
A logical value if the distance to the neighboring diagonal
elements should be calculated exactly, as sqrt(2) , or it should
be set to 1, same as that for the neighbouring pixels on the vertical and
horizontal axes. |
... |
Reserved. |
Given a binary or gray scale image with background set to 0, a distance map transform generates an image each pixel of which contains the distance from that pixel to the nearest background pixel (zero) or the edge of the image.
If foreground constitutes more than 95% of the image, computation of a distance
map can be very lengthy as the function uses an iterative algorithm. This is a
very rare situation anyway and the value of bg
provides a protection
mechanism, e.g. in case a very noise image is supplied performing a threshold
first.
This function is used extensively in object detection. Distance map is a standard
input for the watershed
algorithm used to identify and separate
closely positioned objects.
A Grayscale
object of Image
with pixels
containing the floor
values of their distances to the nearest
background points. The range of the resulting image is [0,n]
, where
n
, a positive integer, will be the distance from center of the largest
object.
To preview the results visually, use display(normalize(result))
.
Oleg Sklyar, osklyar@ebi.ac.uk, 2006
Image, watershed, thresh, propagate
## Not run: see ?watershed for an example