Hacking Raspberry Pi (2014)

Alrighty then! As you can see in Figure 16.5, the Raspberry Pi and the Camera Board are now (hopefully) a functional unit.

FIGURE 16.5 The Raspberry Pi and the Camera Board add-on make a nice pair, don’t they?

Using the Camera Board

The Raspberry Pi Foundation provides two command-line utilities for using the Camera Board:

raspistill: Used to take still images in both JPEG and RAW formats

raspivid: Used to record video by using the H.264 codec

In the next section I cover how to use raspistill to take still pictures. In the section that follows I turn your attention to shooting full-motion video (FMV) using raspivid.

Capturing Still Pictures

Let’s begin by obtaining some command-line syntax help:

raspistill | less

Figure 16.6 shows you the screen output for raspistill; this should serve as a nice reference for you.

FIGURE 16.6 raspistill command syntax

You can also download the full documentation for the Camera Board commands from http://is.gd/18PvNf.

To tell your Pi to snap a picture, enter the following command:

raspistill -o myimage.jpg

When you run raspistill, you see an LED light up on the Camera Board for approximately four seconds; the image is exposed just before the LED goes out.

Any photographs you capture are stored in your present working directory. Thus, if you execute the raspistill command in the context of your home directory, that’s where your files reside by default.

The -o switch enables you to name the images using whatever file name you input after the switch, myimage.jpg in this example.

From LXDE, you can double-click the image files to open them in your default web browser. Alternatively, you can right-click them and select ImageMagick (display) to open them in the ImageMagick open source image viewer.

Despite the lack of a flash or manual focus override, the picture quality is actually pretty good. Take a look at Figure 16.7 to see yours truly posing for your viewing (and laughing) pleasure:

FIGURE 16.7 Despite the poor subject, you can see that the Raspberry Pi Camera Board takes a pretty good picture.

Let’s buzz through some more sample syntax to give you a better idea as to what raspistill can do for you. You can, for example, tell your Pi’s camera to take a picture at a set delay or image quality.

Take an image with a quality of 50% and a “shutter” delay of 10 seconds:

raspistill -o image3.jpg -q 50 -t 10000

The -q parameter goes from 0 (lowest quality) to 100 (highest quality). Quality, in this case, refers to the degree of JPEG compression that is applied to captured images. JPEG is a lossy compression algorithm, so even images taken at quality 100 will have some pixel loss due to the file format.

The timer value adds an exposure delay and works in thousands of seconds (milliseconds). Thus, a value of 5000 represents a 5 second delay.

Take an image with custom dimensions, verbose command output, a quality of 80%, and a one-second delay:

raspistill -v -w 1024 -h 768 -q 80 -o image4.jpg -t 1000

The verbose (-v) parameter is useful for educational and troubleshooting purposes. In fact, let me show you the output of the previous raspistill command example:

pi@raspberrypi ~ $ raspistill -v -w 1024 -h 768 -q 80 -o image4.jpg -t 1000 >
output.txt

raspistill Camera App v1.2

Width 1024, Height 768, quality 80, filename image4.jpg
Time delay 1000, Raw no
Thumbnail enabled Yes, width 64, height 48, quality 35
Full resolution preview No

Preview Yes, Full screen Yes
Preview window 0,0,1024,768
Opacity 255
Sharpness 0, Contrast 0, Brightness 50
Saturation 0, ISO 400, Video Stabilisation No, Exposure compensation 0
Exposure Mode 'auto', AWB Mode 'auto', Image Effect 'none'
Metering Mode 'average', Colour Effect Enabled No with U = 128, V = 128
Rotation 0, hflip No, vflip No
ROI x 0.000000, y 0.000000, w 1.000000 h 1.000000
Camera component done
Encoder component done
Starting component connection stage
Connecting camera stills port to encoder input port
Opening output file image4.jpg
Enabling encoder output port
Starting capture 1
Finished capture 1
Closing down
Close down completed, all components disconnected, disabled and destroyed

Although the previous verbose output looks like so much gobbledygook at first glance, given experience and practice you’ll come to appreciate the degree of detail that raspistill gives you. The verbose output leaves nothing to the imagination, so you can figure out the source of any unexpected behavior you see in taking still pictures with your Raspberry Pi.