[Editor's Note: The instructions and examples in this Tech Talk are based on Adobe Photoshop 7.]
- How to rotate and/or deskew an image.
- How to crop an image.
- How to resize an image.
- How to save an image in a suitable format for e-mail/Web.
If the image is crooked then it is a good idea to rotate it, or you can experiment with cropping and rotating to adjust the style of the image. Here is how:
Go to Image. If it is a black and white image, select "gray scale 8 bits/channel" under "mode." If it is a color image, select RGB or 24 bit color/8 bits per channel. You cannot rotate an image that is in a bitmap (bmp) format without converting to one of these modes. You can change it back later if you want.
Go to Image, Rotate Canvas. If you want to rotate the image 90 or 180 degrees you can do so. If you want to rotate the image just a few degrees, click on arbitrary.
Enter a value for the angle you wish to rotate the image.
Select degrees clockwise (CW) or degrees counter clockwise (CCW). Click on OK.
Press Ctrl-S to save newly rotated image.
Why should I crop an image?
If you want to focus on just one aspect of an image, cut out a blurry spot, remove former friends, or narrow the subject, cropping is a useful tool. Here is how:
Select Crop tool (SHIFT-C).
Click and drag with the mouse to select a rectangular area.
With the mouse you can click and drag at the edge of the selected rectangle to manipulate edges/corners or rotate the rectangle.
After the rectangle is selected, right click on the mouse and select "crop" or "cancel."
All content outside the selected rectangle disappears.
Press Ctrl-(S) to save the newly cropped image.
Older computers and slower Internet connection speeds have trouble opening extremely large files. When you are e-mailing images, or putting them on a Web page you want them to be a manageable size for your users or clients. If you want archival quality prints however, you want to have an image that a professional printer can use. Here is how:
Go to Image, click on Image size.
Check the box marked Constrain Proportions if you want to maintain the dimensions of the image. Deselect Constrain Proportions if you want to make an adjustment without affecting the other values (for example, if you want to change the height but not the length). Constraining the proportions prevents distorting the image.
Selecting a higher resolution does not increase the quality of the image, but choosing a lower number makes the image smaller and more manageable for Web publishing or e-mail.
If you want to e-mail the images, it is best to not go higher than 600 dpi (dots per inch). If you plan to print 4 x 6-inch photos, do not go lower than 600 dpi. If you want to print 8 x 10-inch prints, or 11 x 14-inch prints, you might have an image that is 4000 dpi (30 - 60 megabytes). Of course, if you want to email the image to someone who may be printing it, by all means, opt for a higher resolution. Be aware though that you might fill their mailbox inbox, or your own outbox, depending on the network's limitations. Note the difference between the uncompressed TIF file size and the compressed JPEG file size in the following screen shots.
55 megabytes will slow down or even jam many computers or e-mail accounts. 164 kb is much more manageable.
Go to File: Save As.
Under the format section, select JPEG for general printing, Web publishing and e-mail.
This is the most widespread and accessible file type.
Select TIFF for archival quality prints and digital master copies if you need to save the image for long-term use. The disadvantage is that they are a bit unwieldy within certain programs or with slower Internet connections.
GIF, PNG and BMP are other options that might be specifically requested by certain users or firms, and they are sometimes used for simple graphics in Web design. But if you want to print an image, these file types are unpractical.
About the Author: At the time of this Tech Talk, Nathan Hall worked as a graduate library assistant (GLA) in the UNT Libraries' Digital Projects Unit.