Tip #1666 - JPEG Compression Basics
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WorldStart
As you probably
know, JPEGs are the most common type of file format for digital photography.
They do a fantastic job at compressing an image and maintaining good quality.
For more on image formats, check out:
http://www.worldstart.com/tips/tips.php/546
Now, when
you go to save a file as a JPEG, your imaging software may give you some options—that's
what we're going to look at today.
The first
and most common option is the ever-exciting quality setting. It's usually pretty
easy to understand—the higher the number, the better your image will look,
but the bigger it will be.
How high
you set this will depend on your usage. If you want the best quality, use a
higher setting and live with a larger file size. If you're short on space, try
one of the medium settings. If you need to send the image to someone on dial-up,
be kind and use one of the lower settings. Only you can decide how much
quality is "good enough".
Let's look
at how much quality is really lost when you go with lower settings. Let's take
this image:
Now, here's
a close-up of a window at high, medium, and low quality:
1. Highest
quality (12):
2. Medium
Quality (6):
3. Low
Quality (2):
Although
the low quality doesn't look so great (still not too bad though), there really
isn't much difference between the highest setting and the medium setting. So,
keep this in mind next time you're trying to decide how much compression you
need.
Also, note
that some software will show you how big the finished file will be—really
helpful If you're sending it off in an e-mail or using it on a webpage.
OK, that's
the standard stuff, but many programs also offer you some format options. Here
are the three most common:
Baseline
(Standard) — This is your garden variety JPEG. It's just saved as normal,
nothing special, yawn.
Baseline
Optimized — This is like the above, but you get a little more compression
while retaining the same quality. Used to be some web browsers wouldn't support
this, but that pretty much went out with Netscape1.0.
Progressive
— This is the coolest of the three, at least for web designers. Have you
ever been on a website where you saw a picture download in "waves"?
You know, at first it's kind of chunky and blurry, then another pass goes by
and it looks a little better, then finally it gets nice and sharp? That's what
this does.
If you have
an option for "progressive", then you probably also have an option
for the number of scans—this is simply the number of "waves"
the picture needs to go through in order to download.
That's it!
Probably more than you ever wanted to know about JPEGs!
Happy shooting!
~ Steve
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