Hi there,
This is very easy as you thought. The actual method is very much decided by
what image editing software you have.
There are two basic methods and the result of either is known as "Cropping"
1) Using your image editing software, determine the width and height of the
image. Lets suppose that it is 450 wide by 300 high. To get the ratio of 4 x 3
it is obvious from the numbers given that you need to remove 50 pixels from the
width of the picture....exactly where you remove the width...all from one side
or some from the left and the rest from the right hand side is going to be down
to the content of the picture and your own preferences. So using whatever tool
exist in your image program you reduce the width or height of the image so that
the aspect ratio required is achieved. This may include reducing the size of
the canvas by simply telling the program the new required width and from which
side to take away the excess or it may mean using a Crop tool. This usually
looks like a rectangle made of feint dotted lines and this is where it gets
close to method two. You position your cursor at the top left position of your
picture and at the point where the crop is going to occur, you then press and
hold down the mouse button and drag the mouse to the bottom right corner....you
then release the mouse and via the programs edit menu you tell the program to
crop the image. The new cropped image will replace the old image.
2) Some programs give you the ability to dictate in advance how a rectangular
selection device must perform, these include free hand, a fixed size in pixels
high and pixels wide or a ratio. The option you would use here will be the
ratio option...so by telling your program that you want a 4 x 3 ratio, when you
attempt to use the selection tool you will find that once you start from the
top left corner you will only be able to affect the size of the box and not the
ratio of width to height.. This is the method I use and its very quick....you
don't have to work anything out and if you decide that the box drawn is not in
the right place you can change it by simply re-drawing the box.
I would not be surprised to hear that there are other methods available in
programs I have not seen.
PLEASE TAKE CARE AND EDIT COPIES OF YOUR IMAGES...NOT THE ORIGINALS
So, take a look at what image editing software you have, and look for the crop
tool or the canvas editor....and have fun !!!