imageTogray {measuRing}

Gray matrix

Description

This function can compute a gray matrix from the RGB in an image section. Such an image section can be compressed in either portable network graphics format (png) or tagged image file format (tif).

Usage

imageTogray(image, ppi = NULL, rgb = c(0.3, 0.6, 0.1), p.row = 1)

Arguments

image

character. path of an image section.

ppi

NULL or integer. If NULL the image resolution in points per inch is extracted from attributes in image. If this attribute is not embedded then users should provide it

rgb

vector with three fractions, all of them adding to one, to combine RGB channels into gray matrix.

p.row

proportion of rows of gray matrix to be processed.

Value

a gray matrix containing the image reflectances.

Author(s)

Wilson Lara, Carlos Sierra, Felipe Bravo

Examples

## (not run) Read two image sections in package measuRing:
image1 <- system.file("P105_a.tif", package="measuRing")
image2 <- system.file("P105_a.png", package="measuRing")
## (not run) compute a gray matrix:
gray <- imageTogray(image1)
## (not run) - the ppi is embedded in the image:
attributes(gray)
## (not run) but, the ppi is not embedded in image2:
## - imageTogray will return an error:
## (uncoment and run):
## gray2 <- imageTogray(image2)
## attributes(gray2)
## - the ppi should be provided (i.e. ppi = 1200):
gray3 <- imageTogray(image2,ppi = 1200)
attributes(gray3)
##(not run) a plot of the gray matrix        
xrange <- range(0:ncol(gray)) + c(-1,1)
yrange <- range(0:nrow(gray)) + c(-1,1)    
{plot(xrange,yrange,xlim=xrange,ylim=yrange,xlab='',
      ylab='',type='n',asp=0)
rasterImage(gray,xrange[1],yrange[1],xrange[2],yrange[2])}