Page 205 - MATLAB Recipes for Earth Sciences

200 8 Image Processing

reads and decompresses the JPEG fi le, and imports the data as 24-bit RGB
image array and stores the data in a variable unconform1. The command

whos

shows how the RGB array is stored in the workspace:
Name Size Bytes Class
unconform1 729x713x3 1559331 uint8 array
Grand total is 1559331 elements using 1559331 bytes
The details indicate that the image is stored as a 729x713x3 array represent-
ing a 729x713 array for each of the colors red, green and blue. The listing of
the current variables in the workspace also gives the information uint8 array,
i.e., each array element representing one pixel contains 8-bit integers. These
integers represent intensity values between 0 (minimum intensity) and 255
(maximum). As example, here is a sector in the upper-left corner of the data
array for red:

unconform1(50:55,50:55,1)
ans =
174 177 180 182 182 182
165 169 170 168 168 170
171 174 173 168 167 170
184 186 183 177 174 176
191 192 190 185 181 181
189 190 190 188 186 183
Next we can view the image using the command

imshow(unconform1)

which opens a new Figure Window showing a RGB composite of the image
(Fig. 8.1).
In contrast to the RGB image, a grayscale image only needs one single
array to store all necessary information. We convert the RBG image into a
grayscale image using the command rgb2gray (RGB to gray):

unconform2 = rgb2gray (unconform1);
The new workspace listing now reads:

Name Size Bytes Class
unconform1 729x713x3 1559331 uint8 array
unconform2 729x713 519777 uint8 array
Grand total is 2079108 elements using 2079108 bytes
where you can see the difference between the 24-bit RGB and the 8-bit gray-