You will not only learn to program C$++$ in this class, we will also show you some other things. One of these things is the plain PGM image file format.

You will be working with this image format in this class.

Many applications have PGM support built$-$in$.$ Unfortunately, Windows does not currently come with an app which can display PGM images. $($MacOS

Sierra$$s Preview app can display PGMs$.)$ On Windows, you can download IrfanView if you need a viewer. It is highly recommended that you have a

program to view these files. For Macs, MacOS Sierra has finally added support for PGM images to the all$-$purpose viewer Preview, but you can also

use ToyViewer $($available free on the App store$),$ which I find convenient for image viewing.

For Irfanview, uncheck $$Use Resample for fitting$$ and $$Use Resample for zooming$$ under $$View $|$ Display Options$.$ Otherwise $($by default$)$

Irfanview blurs images when you zoom them. That$$s great for general image viewing, but awkward for programmers trying to figure out what their

program just wrote out to a PGM file.

The complete specification for the PGM format can be found on the netpbm website $($look for plain PGM$)$ or in Wikipedia: Portable Pixmap. A plain

PGM file is just a simple text file that follows the following standard:

The first element in the file is the text $$P$2$

The second and third elements specify the size of the image $($width and height, in number of pixels$)$

The fourth element specifies the maximum gray value $($maxval$)$ This is the largest number that can appear in the actual image data

After that, each line consists of a line of image data, given in gray$$values where $0$ is black and whatever the maxval is is white.

$[1]$

$($These are grayscale images$$ there is a $"$P$5"$ color version called PPM$$ see the netpgm site above for more information.$)$

given all this, here's an example:

P$2$

$147$

$15$

$00000000000000$

$0100001000151515000$

$01010010100015001500$

$01001001000151515000$

$010000100015001500$

$0100001040151515040$

$00000000000000$

You can download the image: mb$.$pgm

All the fields $($header & pixel values$)$ are actually free$-$format, so you$$ll commonly see all the header information on the same line:

P$214715$

$0000000...$

You can also read and display PGM images in matlab with a simple script like this:

I $=$ imread$(\text{'}$mb$.$pgm$\text{'})$

imshow$($I$)$

As an image, mb$.$pgm looks like this $($if you zoom it about $40$x$).($It$\text{'}$s Max Berger's initials...$)$