The Language of Technical Computing
This example shows how to perform arithmetic on integer data representing signals and images.
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Load measurement datasets comprising signals from four instruments using 8 and 16-bit A-to-D's resulting in data saved as int8, int16 and uint16. Time is stored as uint16.
load integersignal % Look at variables whos Signal1 Signal2 Signal3 Signal4 Time1
Name Size Bytes Class Attributes Signal1 7550x1 7550 int8 Signal2 7550x1 7550 int8 Signal3 7550x1 15100 int16 Signal4 7550x1 15100 uint16 Time1 7550x1 15100 uint16
First we will plot two of the signals to see the signal ranges.
plot(Time1, Signal1, Time1, Signal2); grid; legend('Signal1','Signal2');
Here we see the values for int8. It is likely that these values would need to be scaled to calculate the actual physical value that the signal represents e.g. Volts.
We can perform standard arithmetic on integers such as +, -, *, and /. Let's say we wished to find the sum of Signal1 and Signal2.
SumSig = Signal1 + Signal2; % Here we sum the integer signals.
Now let's plot the sum signal and see where it saturates.
cla; plot(Time1, SumSig); hold on Saturated = (SumSig == intmin('int8')) | (SumSig == intmax('int8')); % Find where it has saturated plot(Time1(Saturated),SumSig(Saturated),'rd') grid hold off
The markers show where the signal has saturated.
Next we will look at arithmetic on some image data.
street1 = imread('street1.jpg'); % Load image data street2 = imread('street2.jpg'); whos street1 street2
Name Size Bytes Class Attributes street1 480x640x3 921600 uint8 street2 480x640x3 921600 uint8
Here we see the images are 24-bit color, stored as three planes of uint8 data.
Display first image.
cla; image(street1); % Display image axis equal axis off
Display second image
image(street2); % Display image axis equal axis off
We can scale the image by a double precision constant but keep the image stored as integers. For example,
duller = 0.5 * street2; % Scale image with a double constant but create an integer whos duller
Name Size Bytes Class Attributes duller 480x640x3 921600 uint8
subplot(1,2,1); image(street2); axis off equal tight title('Original'); % Display image subplot(1,2,2); image(duller); axis off equal tight title('Duller'); % Display image
We can add the two street images together and plot the ghostly result.
combined = street1 + duller; % Add |uint8| images subplot(1,1,1) cla; image(combined); % Display image title('Combined'); axis equal axis off