Page 204 - MATLAB Recipes for Earth Sciences

8.3 Importing, Processing and Exporting Images 199

5. In 1986, the Joint Photographic Experts Group ( JPEG) was founded
for the purpose of developing various standards for image compression.
Although JPEG stands for the committee, it is now widely used as the
name for an image compression and format. This compression consists of
grouping pixel values into 8x8 blocks and transforming each block with
a discrete cosine transform. Subsequently, all unnecessary high-frequen-
cy informaiton is eased. Such practice makes the compression method
irreversible. The advantage of the JPEG format is the availability of a
three-channel 24-bit true color version. This allows to store images with
smooth color transitions (http://www.jpeg.org/).

6. Portable Document Format (PDF) – The PDF designed by Adobe
Systems is now a true self-contained cross-platform document. The PDF
files contain the complete formatting of vector illustrations, raster im-

ages and text, or a combination of all these, including all necessary fonts.

These files are highly compressed, allowing a fast internet download.
Adobe Systems provides a free-of-charge Adobe Acrobat Reader for all
computer platforms (http://www.adobe.com/).

7. The PICT format was developed by Apple Computers in 1984 as the na-
tive format for Macintosh graphics. The PICT format can be used for
raster images and vector illustrations. PICT uses various methods for
compressing data. The PICT 1 format only supports monochrome graph-
ics, but PICT 2 supports a color depth of up to 32-bit. The PICT format is
not supported on all other platforms although some PC software tools can
work with PICT fi les (http://www.apple.com).

8.3 Importing, Processing and Exporting Images

Firstly, we learn how to read an image from a graphics file into the work-

space. As an example, we use a satellite image showing a 10.5 km by 11 km
sub-area in northern Chile:

http://asterweb.jpl.nasa.gov/gallery/images/unconform.jpg

The fi le unconform.jpg is a processed TERRA– ASTER satellite image that
can be downloaded free-of-charge from the NASA web page. We save this
image in the working directory. The command

unconform1 = imread('unconform.jpg');