readTiff: A function to load TIFF images into a pixmap.

In rtiff: Read and Write TIFF Files

Description

Loads a TIFF image from a file and returns the image as a pixmap object, with optional scaling.

Usage

readTiff(fn, page = 0, reduce = 0, pixmap = TRUE)

Arguments

fn	Filename (the tiff image to load)
page	In the case of multi-page tiffs, which page do you want?
reduce	Optional scaling factor to improve performance with large images, should be a value between 0 and 1 (i.e. a decimal representation of a percentage). See details.
pixmap	By default, readTiff returns a pixmap object, ideal for plotting. However pixmap rescales the values to [0..1]. If you want the raw values from the file, set pixmap=FALSE to get a list of r, g, and b values, unscaled.

Details

This package is a wrapper around libtiff (www.libtiff.org), on which it depends. By using libtiff's high level TIFFReadRGBAImage function, this package inherently support a wide range of image formats and compression schemes (interestingly, thanks to libtiff, this package can load a number of TIFF formats that tools like Window's Paint or the open source Gimp application will not load).

High resolution images (by which I mean images that contain a "large" number of pixels) will occupy quite a bit of memory and will also plot very slowly. If you do not need all the resolution for your purposes, you scan specify a scaling factor (reduce=x) to downsample the image. The factor is the amount you want the image scaled BY, not TO. In other words, reduce=.90 will reduce the image by 90 yielding an image 10 approach is used. Since we are reducing and not enlarging, I hope this will be suitable for your applications.

For simplicity, an RGB pixmap is generated regardless of the colorspace of the original image (including grayscale images, in which case the R, G, and B rasters are identical). The pixmap object requires pixel intensities to be between 0 and 1, so the intensities in the original image file are scaled accordingly. Alternatively, specify pixmap=FALSE to return a list of unscale r, g, and b values instead of a pixmap object.

Value

A pixmap object containing the image rasters.

Author(s)

Eric Kort <[e-mail]>

Examples

tif <- readTiff(system.file("tiff", "jello.tif", package="rtiff"))
plot(tif)

Example output

Loading required package: pixmap

rtiff documentation built on Jan. 14, 2021, 5:20 a.m.