Have you ever needed a stock photo or illustration and wondered which kind of stock image to purchase?
The first thing to remember is that two factors are important in your choice: image size and image resolution. Think of this as two realities for the image. The first is a two-dimensional size measurement of height and width. The second—the resolution, or dpi (dots per inch) or ppi (pixels per inch)—is like a three-dimensional measurement.
To experience choosing a stock image, go to iStock and search for birds in a tree. Click on a photo or several photos, and review the choices available to you. You see that the categories are:
size
pixels or inches
file size
credits (this is the pricing)
When you click on inches, you will see the size in inches as well as the resolution (72 or 300 dpi). 72 dpi is acceptable only for a web image; choose 300 dpi for any other publishing. Be sure to choose a bigger size than you need, within reason. You can always downsize an image in Photoshop without losing anything, but when you make it larger in Photoshop, you will loose some resolution.
You may want an illustration instead of a photo. Search for an illustration on iStock, GraphicLeftovers, Canstock, Dreamstime or many other sites. Purchase an EPS vector image if it's available. Vector means the image is scalable to large sizes, because image is generated by mathematical vectors; it is not pixel-based. I write EPS vector because some JPGs are based on a vector image and lack editing features.
To resize a vector image in Photoshop, download an image and open it in Photoshop. You will see a dialog box that says “Rasterize EPS Format.” Choose RGB at 300 ppi, 20 inches Then examine the crisp detailed image.
If you want to quickly modify colors and shapes in an EPS vector, you need an editing program such as Adobe Illustrator or Inkscape.
Eric runs Photo Grafix, a humble photo-retouching studio in Evanston, Illinois (USA), making photo illustrations and improving photos for hundreds of people and companies worldwide.
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