Bitmap Graphics in Photoshop

bee_and_blossoms_thumb
Bees and Blossoms

Everyone knows that Photoshop is an extremely powerful program which can be used to create a rich variety visual of materials for the web, print, animation and 3D. However for first-time users it can seem a bit of a monster, far more difficult to operate than other programs they have used. For starters, you might ask why you can’t just simply click on the things you see in a picture in order to select them? The reason is that, while the majority of programs used by most people on a day-to-day basis are vector-based, Photoshop is a raster-based, or bitmap program. In order to tame the beast, you need firstly to understand what that means and how it makes working in Photoshop different. By the way, the words Raster and bitmap are synonyms and thus can be used interchangeably. So what do they mean?

Have you ever tried to increase the size of a small image copied from a website? If you have, then you may have noticed that it ends up looking terrible, with jagged-looking edges all over the place. Have a look at this example:

bee_and_blossoms
Original size
bee_and_blossoms_closeup
Enlarged
bee_and_blossoms_pixelated
Detail

Welcome to the world of the bitmap image! The reason that we see all those little squares is because of the underlying structure of this image – namely the bitmap. Bitmaps are made up of a grid of tiny squares called pixels, and the number of pixels in the grid is fixed. Each and every pixel can be a different colour and so bitmaps are perfect for recording the detail required in photographic images. In our example, what our eye naturally detects as a bee collecting nectar from blossoms, is actually just a whole bunch of differently coloured little pixels. When we make the image bigger, because the number of pixels still remains the same, the pixels just become bigger and thus more and more noticeable. If we keep making it bigger, the original picture seems to be nothing more than an abstract study of colour.

This ‘grid of pixels’ structure is why you cannot simply click on the bee in order to select it. That bee consists of hundreds, or maybe even thousands of pixels, each of which could be selected individually. Here is the essence of the beast – in order to select things in bitmap images, we have to more or less trace around the perimeter of all those pixels!

The reasons for selecting parts of an image are almost endless, beginning with the basics e.g. to cut, copy or move the item to more complex requirements such as recolouring, extracting something from it’s background, filtering, applying effects or retouching. Thankfully, Photoshop comes with a large variety of tools and techniques to help with this sometimes daunting task of selecting things in an image. Now that we’ve established what a bitmap is, you are now ready to begin the Photoshop journey.

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