Week 1 (Part 3: Working with documents)

Image Size and Resolution

The Image size dialogue box is under the [image] menu. This is where you can edit the dimensions/resolution of your images. Resolution is usually referred to in Pixels Per Inch (PPI) or Dots per inch (DPI). A good understanding of this dialogue goes a long way. As confused as a lot of people get with this adjustment, it's really quite simple. The Pixel Dimensions state the width of the image in pixels and the height of the image in pixels. When changing the image size you can achieve one or two goals either independently or simultaneously. You can change the resolution of the image (up or down) while keeping the physical height and width dimensions the same. Or you can change the physical dimension while keeping the resolution the same. You can even do both adjustments in one operation.

Example:
A 2" x 2" square image at 150 PPI (Pixels per inch) would be a total pixel dimension of 300 pixels x 300 pixels. This would be exactly the same as having a 1" x 1" square image at 300 PPI. It would also be a total pixel dimension of 300 pixels x 300 pixels. The only difference between these 2 images is that if you printed them out, one would be a 1" square while the other would be a 2" square.

*Changing the physical size while leaving the resolution alone does not take any processing time.

When increasing the resolution of an image, Photoshop needs to create additional pixels. It does this through a process called interpolation. There are different modes of interpolation, but for a beginners level we'll just leave it set to bicubic. Leaving this setting on this mode will always give you pretty good results. It's usually the safest bet when in doubt.

Canvas Size

Altering Canvas size is different than altering Image size. Canvas size is most commonly used to expand your image area by adding pixels to the outer edge of your image. The color of that expanded area is determined by the user in the Canvas Size dialogue box at the time the edit is being made. By entering a smaller dimension in the Canvas Size dialogue than the actual image, the result would be a crop type of edit. A warning box will pop up to tell you that you will be cropping out some of the image. The new smaller defined size would be determined from the center of the image outward.

*The relative checkbox in this dialogue box will display only the extended amount of canvas instead of the whole new dimension of the image if it is not check. In this case it is referred to as an absolute size.

Crop Tool

The crop tool allows you to crop parts of your image. It is used very simply by selecting the tool and then dragging over the area you want to crop. Once you draw this area you can fine tune the area by grabbing the handles (square nodes at the corners and center sections of the vertical and horizontal crop lines and moving them.) By holding [shift] while you draw it will constrain the crop area to a perfect square. By holding [shift] and [option/alt] it will draw a perfect square from the center out. To apply this edit, click the check mark in the top tool options bar or press [return/enter].

You can also correct for perspective with this tool. Once you have drawn out a crop area, click to check the [perspective] check box in the top tool bar options. Now when you grab a corner node, it will not constrain to be a straight vertical or horizontal point. Once you have made your adjustments to the crop area apply the edit and it will square up the selection you have made. Pretty nifty!

The Crop tool can also adjust the image size at the same time as the cropping all in one edit. This allows you to perform a crop and a image size adjustment all in one procedure. Throw in a perspective edit at the same time and you've done 3 edits all with one tool in one-fell-swoop.

Guides

Guides can be used to help to layout a composition or align things in your image. To create a guide, simply drag one out from the horizontal or vertical ruler boundaries shown at the top or left of your image(depending if you want a vertical or horizontal guide). If there are no rulers showing, go to the [view] menu and select [Rulers]. This will toggle them on or off.

*If you hold [shift] while you drag the guide out, it will snap to the increments on the ruler marks.