Lesson:Introduction To Photoshop
About These Lessons 
This lesson provides you with an introduction to the program and some of the major concepts that you'll find in future lessons. Please read through the topics below before continuing to another lesson. You can click on any of the hyperlinked words to get more in-depth information about that topic. Please keep in mind that the images and diagrams used in these lessons may be slightly different than your copy of Photoshop.
What is Photoshop? 
Adobe Photoshop is a digital graphics editing program produced by Adobe Systems. It is the leader for commercial Bitmap editing and image manipulation. It is considered by many to be the industry standard for desktop graphics editing and is available for the Windows/Mac operating systems.
To get the most out of these courses, you will need to obtain a copy of Photoshop. You can purchase the full version or download a trial version at the Photoshop Product Page on the Adobe Website.
What Are Layers? 
One of the most important concepts in graphic software is the proper use and manipulation of layers. A layer can be thought of as an individual "slice" of an image that is sandwiched together. The major advantage of using layers is that you can easily manage and edit pieces of your artwork without disturbing the rest.
An easy way to picture this concept is to imagine that you are looking out a window. Now if you were to draw a picture on the window, you would essentially have a layer that can be edited without affecting the background image.
It is important to note that layers are not compatible with some image formats and the image will have to be flattened. Also note that layers will increase the file size and proper management will have to be performed to keep your files healthy and efficient.
What is the Difference Between Vector And Bitmap Graphics? 
Another important concept to understand is the differences between the terms vector and bitmap. More precisely we should understand what a vector image is and what a bitmap image is. These terms describe what type of image you are making and also play a huge role in how that image will be utilized.
Bitmap graphics are the most common type of image. Bitmap images are made up of Pixels, which are tiny colored dots on your monitor that make up images. Screen resolution is a term that specifies that there are 72 dots per square inch of the image (72dpi) which is displayed at 72 pixels per square inch on the screen (72ppi). For editing purposes, the graphic standard is 300dpi so that there is enough information available to play with. The main disadvantage of using bitmap images is that when you resize the image, you will lose quality and the picture will start to look "blurry" or "pixelated". This is particularly true when making images larger and is due to forcing the image, which has a set number of pixels, into a larger size. Thus if a 72dpi, 1" x 1" red square has 72 pixels and were enlarged 200%, it would be forced to become 2" x 2" and 288 pixels. The extra pixels are formed by taking the difference in color between the surrounding pixels. The red square would look fine for the most part, but only because it is one color.
In contrast, vector images are made up of resizable paths. You can enlarge or reduce vector images and they will retain their quality perfectly (keep in mind that the screen displays everything at 72dpi/ppi, so sometimes they do not appear perfect). The major disadvantage of using a vector image is the amount of effort required to produce a highly detailed image. We will talk more about when to use a vector image and when to use a bitmap image in future lessons.