TUTORIALS

Pixels and Resolution

Forget what you know about resolution. It's a misleading concept, and is one of those computeree concepts that is deceptively straightforward. You may have heard resolutions quoted in dpi or ppi (dots/pixels per inch). This is relevant if you are printing an image on paper. If you deal only with computer images ignore resolution! Concentrate on these two facts:

1) Computer screens have fixed number of pixels (variable in discreet steps - usually horizontal resolutions are 800, 1240, 1600 pixels).

2) Only the pixel dimensions of images are relevant for displaying images on a computer.

So if your screen resolution is 1024 and your picture is 512 pixels wide then it will cover exactly half of the screen width. Get it?

Furthermore...

You may have heard that computer images should be scanned at 72 dpi. Well...lets say your resolution is 1024 wide. And your monitor happens to be 12 inches wide (a 17" monitor). Then your resolution of your screen is

1024 ÷ 12 = 85.33333 pixels per inch.

Screen resolutions tend to vary between 72 and 96 dpi. People use these numbers for computer imagery and scanning because a scan at these resolutions will give an image that is roughly the same size on the monitor as it is in real life.

Printing...

Think about the number of pixels in an image and the size you want to print it. If your image is 2048 pixels wide and you want to print it 5 inches wide then your print resolution is

2048 ÷ 5 = 409 pixels per inch (dpi).

So how big can you print a 2048 pixel-wide image? In practice you can drop down to 200 dpi or even 150 on a desktop printer So

2048 ÷ 200 = 10.24 inches wide.


Now if you try and print that 512 pixel-wide image - at 300 dpi it will be

512 ÷ 300 = 1.7 inches wide!

In practice if you print it at 72 dpi it will look slightly fuzzy but at least it will be roughly the same size as it was on the screen.

Heres a methodology:

The following sections give suggestions for how to deal with images for use in different media.

FOR PROFESSIONAL PRINTERS

· Don't do anything to them!

Printers will want the highest resolution possible. If you make the images bigger you are just spreading 1 pixel over two - you wont gain any resolution.

· If you manipulate them (crop or change colour) save them as a tiff or psd (photoshop file) in a separate folder.

This is because the jpeg format is LOSSY. Save it as a jpeg again and it compounds the lossiness - like re-photographing a photograph.

FOR EMAILS

This is for viewing on a monitor so ONLY PIXEL DIMENSIONS are important (see First off)

· Resize your image in photoshop or acdsee to make it about 400 - 500 pixels long (at its longest - ie about 300 pixels wide if its upright)

To resize in photoshop go to image>image size and alter the pixel dimensions (top box) FORGET ABOUT THE OTHER BOXES.

FOR PRINTING ON A DESKTOP PRINTER

Ideally you want to print at 300 dpi or more.

· More likely than not - DON'T DO ANYTHING!

Let the application you're using resize the image. In photoshop use the print options dialogue box (file menu). If your image is smaller than you would like you can scale it up here - you'll get lower dpi, but you wouldn't really add any pixels by scaling its image size up anyway.

Unless...

The pixel dimensions of the image are very small - if your print out is "blocky" in appearance then you will need to "resample" the image - this will add more pixels - not necessarily increasing the resolution, but smoothing out the blockiness

FOR CD

Depends how you are presenting them.

You want the absolute maximum size of the picture to be the clients/ viewers likely screen resolution.

· If they are viewing at 800x600 make the image 800 pixels wide at most (this would be a safe bet, as most people now have resolutions set higher).