Change Image Size

These are notes on the Adobe video.

Resize an Image

Open resize.jpg from the downloadable practice files for this video. In most cases you will want to start with an image that is larger or at least not a lot smaller than the resized image you need. This is because if you enlarge the image a lot, it can look blurry.

If you click at the lower left and choose Document Dimensions, you will see the dimensions of this image (1800 pixels wide, 1200 pixels high) and the resolution (100 pixels/inch).

Choose Image > Image Size, which will open the Image Size dialog box. You can drag the lower right hand corner to make it bigger. On the left you will see a preview of the image and on the right, the controls for changing image size. To resize for the web, here are some things to check:

• the icon to the left of the height and width is on (has a dark shading). This will ensure that the proportions (the aspect ratio) do not change from the original image. This will prevent the image from looking squeezed or stretched.
• the resample box is checked - this says Photoshop can throw away some pixels when making the image smaller, or add some when making it larger. When you are resizing an image for the web, typically you will want this box to be checked because your original will generally have a larger file size than is desirable for the web where download times are important, so you typically will want to get rid of some pixels to make the file size smaller.
• the size units are correct - if the image will be displayed on screen, the units should be changed to pixels

If you make changes in the entries, the new file size will be shown.

When you are done, choose File > Save As, to avoid changing the original.

Set the resolution

Open Resolution.jpg. Choose Image > Image Size. The Image Size dialog box shows the dimensions of the image as 1800 pixels wide by 1200 pixels high. However, if you were going to print this image, you would measure its size in inches. Since the resolution is 100 pixels per inch (which applies both vertically and horizontally), this means that the image would print as 18 inches wide and 12 inches high. Change the units in the height and width from pixels to inches, and the height and width number will adjust based on the resolution.

The resolution you choose will depend partly on what printer you use. For an ink jet printer, you might choose 300 pixels/inch.

You want to make sure than the resample box is unchecked because we don't want to change the total number of pixels in the file (since it will be printed, so we don't need to worry much about file size). Furthermore, if we increase the number of pixels per inch, we would want the image size to get smaller as opposed to adding pixels to maintain the same physical dimensions.

So you can change the resolution in the dialog box to 300 pixels per inch and the height and width figures will adjust automatically.

Crop and Straighten an Image

Open Crop_Straighten.jpg. Select the Crop Tool (first column, third from the top). You can drag in from the side or the corners.

• The areas to be cropped away will be shaded grey so you can tell what you will lose relative to what will remain
• By default, the "Delete Cropped Pixels" in the options bar will be checked. This means that when you finalize the crop and save the image, those pixels will permanently be lost.
• The video suggests unchecking the box. Even if you have committed the crop (e.g. by clicking the check mark), you can select the crop tool again and click on the image and the cropped pixels will show up. By so doing, you can later change the crop; the previously-cropped pixels are still available. Try this.
• When you drag in from the sides or corners, you will notice that the area that will remain after the crop is divided by two horizontal and two vertical lines, each equally spaced. There is a rule of thumb or guideline called the "rule of thirds" (first written down in 1797) which proposes than the important elements of an image should be positioned these lines or at the intersection of them rather than simply centering them. (see https://en.wikipedia.org/wiki/Rule_of_thirds for examples; the lines show up when you cursor over the image)
• Straighten option - this video shows that the line you draw after clicking the straighten option need not be at the edge of the image, as was the case in the Straighten example used in Chapter 2 of Adobe Photoshop Classroom in a Book (2021 Release). In this image for example, we could use the table edge as the reference point for this line.

Expand the Canvas

There may be cases where you want to expand the canvas beyond your original image in order to add text or other content to your original design. Open Expand_Canvas.jpg

Choose Image > Canvas Size. This is different than Image Size; Canvas Size doesn't change the size of your image, it just allows you to add additional space around the image. The dialog box that shows will, by default, show size in inches. If you are preparing an image for the web, you will want to change the units to pixels; changing either height or width will change the other dimension as well.

If you know the absolute size you want to end up with, you can enter it, but often you will want to check the relative box which sets the height and width to 0, and now you can type in the number of pixels you want to add for height and/or width. Suppose you enter 400px for the width and nothing for the height. When you click OK, Photoshop will add half of the pixels on the left hand side and half on the right hand side.

Suppose you want to add them just on one side, say the right side. Click the arrow on the left hand side in the Anchor section. This tells Photoshop to anchor the image to the left side of the canvas and hence pixels will be added to the right. This time specify 800 pixels and you will see that they are added on the right.

So far the canvas extensions have all been white. But you can control the color of your canvas extensions, using the canvas extension menu. If you are not on a Background layer, the canvas extension menu will not show up and your extension will be transparent and will appear as a grey and white checkerboard in Photoshop. If the layer is a Background layer, it can be converted to a regular layer by right-clicking on the layer and choosing "Layer from Background".

Revised: April 20, 2021. Comments to Bill Pegram, wpegram@nvcc.edu