PhotoShop Image Size and Resolution
Resolution, or DPI refers to the number of dots, or pixels, on a linear inch of an image. The web displays graphics at 72 DPI, yet sometimes your client will hand you a 300 dpi image. PhotoShop can help you make the transition from a clunky, slow downloading file to speedy 72 DPI delight.
PhotoShop can also help you resize an image. Lets face it, things arent always the way we want them. You can shrink or stretch an image to fit your liking, or you can chop out a small part of an image and make it larger.
The possibilities are endless!
As previously mentioned, all web images should be set at 72 dots per inch. This can be achieved through scanning (scanning chapter next), or by manually changing DPI settings in PhotoShop.
Adding or subtracting pixels is easy. Deciding what color to make the new pixels is another story. How is PhotoShop supposed to know if a new pixel is part of a line, or if its part of someones face? Its just a computer program. PhotoShop doesnt even know what a face is
When changing resolution, PhotoShop runs complicated algorithms on an image to decide exactly how to change it. PhotoShop does an amazing job of adding and subtracting pixels, but it isnt magic. Usually you can only move up or down in resolution by about 1/3 before the image really suffers.
Changing Resolution (but not size) for Web Images
Sometimes youll have an image that was scanned at a higher or lower resolution than you need. Its size is fine, youll only need to change the resolution.
When you instruct PhotoShop to change the size of an image, it merely spreads out or scrunches the image pixels. Pixels spread outimage gets bigger. Viola.
On the other hand, if youre trying to make an image larger, and still keep your current dpi, well then PhotoShops got its work cut out for it. To make an image larger, PhotoShop must spread pixels apart. To keep resolution the same while stretching, PhotoShop must add new pixels to the image and decide what color they should be. When shrinking an image, PhotoShop must decide which pixels to remove.
PhotoShop is really good at adding and removing pixels, but you can generally only increase or decrease size by about 1/3 before images start looking yucky.
Work on a Copy When Changing Sizes
Changing image size actually changes the color information in the image, so you might want to save a copy before resizing an image forty times to decide how you like it. Every time PhotoShop changes the image, it removes or adds pixels, slightly lowering image quality.
Changing Size, but not Resolution for Web Images
Heed this warning:
PhotoShop was designed for both print and web work. Thus, the program gives you the option to change print dimensions or pixel dimensions. As a web designer taking a web design course, you dont care about print size; your only concern is pixel Dimensions. Dont bother changing the print dimensions.
Printing Web Images
Im sure youve tried to print something from the web, and it looked bad, didnt it?
If you positively need to print something you found on the web, you can use this trick.
Basically, youre going to shrink the image. To accomplish the downsizing, PhotoShop will move pixels closer together, resulting in a higher, more printable dpi.
Changing Canvas Size
What if you dont want to change the image size, you just need more room in the PhotoShop window? Maybe youre trying to place two images next to each other, or add text next to an image.
Just like a painting is on a canvas, PhotoShop images are also on a canvas. If you need to add extra space in an image, youll just change the canvas size. The picture wont get any bigger or smaller, but there will be more room around it.
To change the canvas size:
It can be tricky to add canvas in the right direction.
Heres the trick to keep in mind:
Cropping an Image
Youve got a great image, but you only need the center. Cool, were going to chop off the rest using the crop tool.
The crop tool is found on the toolbox.
To Use the Crop Tool
Using The Crop Tool To Straighten A Scan
No matter how hard you try to keep an image straight in the scanner, evil gremlins will knock it off whack right before you close the scanner lid. The scan will come out slightly twistedalmost always happens.
Luckily, you can foil the evil gremlins by using the crop tool.
To straighten an image:
Using the Crop to Enlarge Part of an Image (to Correct Proportions)
Lets say youve got a 100 pixel photograph for your website, its a nice photo, but you dont need the outside edges You want the image to still be 100 pixels, though. Never fear, the crop tool has anticipated your needs and has a special feature just for you. You can choose an area to crop. Youll tell PhotoShop how large that area should be after you crop it. PhotoShop will crop the image, and shrink or enlarge the cropped area to fit dimensions you specify.
To crop to specific dimensions: