How to Resize Images
How to Add Canvas
How to Crop an Image
How to Flip and Rotate an Image
How to Silhouette an Image
How to Use the Heal Brush
The tasks in this part of the book look at the basic skills you need to modify and process most kinds of images. It is inevitable that you will need to resize, rotate, flip, or silhouette almost every image with which you work. These basic tasks are important because you must know how to do them before you can apply more advanced processing. In addition, if you do not properly perform tasks such as silhouetting and resizing, you may destroy image resolution or create less-than-desirable results.
These tasks sometimes are referred to as preprocessing tasks or image prep tasks because they are a precursor or requisite step before more serious work can begin. A better way to look at the process is to consider these tasks as fundamental skills that every Photoshop user must master. Exercising these skills with speed and precision will bring a high level of consistency and quality to all your work.
An area you should pay special attention to is resizing images safely to minimize loss of image quality. Images are made up of small building blocks called pixels; the number of pixels in an image's width and height determines the image's resolution. Consider an image that is 500 pixels high and 700 pixels wide. If you ask Photoshop to increase the image size to 700 high by 900 wide, you are asking it to add pixels. Where do these pixels come from? Photoshop makes them up, using a process called interpolation.
When adding a new pixel, Photoshop looks at the surrounding pixels to determine the value of the pixel it will add. When Photoshop interpolates an image, it can use one of three methods: Bicubic, Bilinear, and Nearest Neighbor. With the Bicubic method, Photoshop looks at the pixels on all four sides as well as on all diagonals and makes a guess at what the new value should be. With the Bilinear method, Photoshop looks only at pixels vertically and horizontally. With the Nearest Neighbor method, Photoshop looks only from side to side to make the decision of what the new pixel should be. As you can imagine, the Bicubic method delivers the highest level of quality for most photographic imagesalthough it takes the longest to process. And, although the Nearest Neighbor method generally provides the lowest quality for photos, it does a great job on hard-edge, graphic shapes and is also the fastest method of interpolation.