TIP: Using pictures - JPEG or GIF? Family History Local History

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TIP: Using pictures - JPEG or GIF?

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Topic: TIP: Using pictures - JPEG or GIF? (Read 145 times)

Zeb
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TIP: Using pictures - JPEG or GIF?
« on: Sunday 15 October 06 23:53 BST (UK) »

Images can make or break a website and it can at times be a little tricky knowing which format to use. I'll only cover JPEG, PNG, GIF and animated GIF. Choosing the right format to store your pictures in can be as important as which colors to use on your site. When I'm asked to tidy up existing sites for people one of the first thing I look at is what images are being used and what format they're using. A few times I've converted images from one format to another and cut the size of pages down to a fraction of their original size.

Bandwidth
Using the right image format also helps to preserve the bandwidth. If you've got a large graphic file [file size] on your home page or at the top of each page then bandwidth usage can soon be eaten up.

If you "borrow" images from other sites you don't have to use them exactly as they are. What looks good on one site could look a lot better reduced in size on yours.

JPEG Joint Photographic Expert Group (.jpg, .jpeg)
A standard way of storing and displaying images with high levels of detail, ideal for photographs. This is a "lossy" format meaning that some of the detail is thrown away and lost forever to help keep the file size down to a minimum. The average setting for web images is 7 or 8. The lower the number the more detail is thrown away and the smaller the file. The higher the number the more detail is kept and the larger the file. You can tell badly saved files as they'll appear to be "blotchy" around levels of detail like where text contrasts against the background. This can be noted on standard satellite and cable TV.

Ideal for: photographs

GIF Graphics Interchange Format (.gif)
Best used when the image contains a very low level of detail like cartoons and is also limited to only 255 colors (256 with transparency mode turned on) so no good for photographs. Be warned that although program X can save a photograph out as GIF some browsers may mess up the image. For example, I've accidentally saved photos out as GIF and they look ok on my PC but on my Mac look terribly distorted.

GIF images have two advantages over JPEG in that they can be animated and/or transparent.

Ideal for: cartoons; page titles in non-standard fonts; logos; icons

PNG Portable Network Graphics (.png)
This mixes most of the best features of JPEG and GIF into one format. They can be transparent and can contain millions of colors as well as being able to store text within the file making it possible for search engines to read them. Because of this be very careful when using existing PNG files which have been "borrowed" from other sites. Its worth noting that PNG is not a lossy format so its ideal for compressing photographs or images where no loss of detail is important.

The only real down-side to using PNG files is that not all browsers fully support the more advanced features like alpha channels and gamma correction although this won't be a problem for most users.

Ideal for: photographs; multi-colored page titles; fancy logos

End Note
Often its a case of trying to find a nice balance between picture quality and small file size. If you're ever unsure which one to use, save an image out in all 3 formats. Then just compare the file sizes against picture quality. If you're using Windows this can easily be done by right-clicking the saved files and selecting "Open With..." then "Internet Explorer"

One good piece of software that can be used for free to convert images from one format to another, resize and more is IrfanView and can be downloaded at http://www.irfanview.com


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