Are bloated images slowing down your web site and causing you lost business? Images comprise over 50% of the average web page so putting them on a diet is essential to improving web performance. One of the best ways to optimize GIFs and PNGs is to minimize the "bit-depth" or the number of colors within your images.
For palette-based formats like GIF and PNG, file size is directly related to the size of the color palette, or the number of colors in the image. As the number of colors in an image crosses a power of two, the file size jumps. A 33-color image must use a six-bit palette, while a 32-color image can use a 5-bit palette. Smaller palettes mean smaller codes (representing pixel patterns), which makes for smaller files. So minimizing the number of colors in index-color images like GIFs and PNGs will minimize file size.
The compression schemes used in GIFs (LZW) and PNGs (Deflate) are dictionary-based encoding algorithms. Dictionary based compression algorithms substitute shorter codes for longer patterns of strings within the data stream. Pixel patterns (substrings) in the data stream found in the dictionary are replaced with a single code. If a substring is not found in the dictionary, a new code is created and added to the dictionary. Compression is achieved when smaller codes are substituted for longer patterns of data.
The code size is based on the number of bits per pixel, and depends on the maximum length code within your dictionary. Thus the smaller your bit-depth, the smaller the codes representing your pixel pattern strings, and the smaller the file.
Choosing the right format for your images is the first step in optimizing web graphics. At lower bit-depths, banding can appear in smooth-toned images. Try quantizing your image to different palettes to minimize banding.
PNG Compression
PNG uses the deflate compression algorithm which is a newer, more efficient cousin of LZW. Deflate is designed to be free of patent problems. Deflate is a combination of the LZ77 algorithm found in zip programs like WinZIP and gzip, and Huffman coding. Deflate typically compresses files 20 to 30 percent smaller than LZW, which is the difference you'll find between gzip and compress. PNGs use a similar substitution technique, but are generally 5 to 25 percent smaller than GIFs, although there are exceptions. In addition to horizontal "scan-line" pattern substitution PNGs sometimes substitute for vertical patterns. PNG can also truncate color palettes. In general, the smaller the color palette, the smaller the overal file size.
Conclusion
To minimize the file size of palette-based image formats like GIF and PNG, minimize their bit-depth, or number of colors. Each time you pass a power of two, file size jumps higher. By minimizing the number of colors, and maximizing the flat-color areas you will create smaller, more efficient images destined for the Web.
Further Reading:
LZW Data Compression
http://www.dogma.net/markn/articles/lzw/lzw.htm
Mark Nelson breaks down the LZW compression algorithm for Dr. Dobb's Journal of October 1989.
Multimedia: Use Lossy Compression for Smaller GIFs and PNGs http://www.dogma.net/markn/articles/lzw/lzw.htm
Lossy compression lets you squeeze more bytes out of your GIFs and PNGs. Lossy compression increases identical pixel patterns to improve compression in indexed-color images.
Multimedia: Use Weighted Optimization
http://www.dogma.net/markn/articles/lzw/lzw.htm
Weighted optimization or regional compression applies different degrees of compression to different areas of your image. By varying the quality within images you can improve file size.
Optimizing Web Graphics
http://www.dogma.net/markn/articles/lzw/lzw.htm
Chapter summary from Speed Up Your Site, shows how to correct, optimize, and compress images for minimum file size and maximum quality.
PNG Home Site
http://www.dogma.net/markn/articles/lzw/lzw.htm
Greg Roelofs site devoted to all things PNG.
About The Author
Article by Andy King, author of the popular new book titled "Speed Up Your Site ? Web Site Optimization". Visit Andy King's web site to learn the best Web Site Optimization practices for higher traffic and speed guaranteed. http://www.dogma.net/markn/articles/lzw/lzw.htm
executive chauffeured services Bradford .. Madison to Airport carIn the region where my company is located, South Bend,... Read More
We've all seen those messages on some websites warning not... Read More
One of the biggest mistakes that most online retailers make... Read More
Although designing a great web site is an important part... Read More
Internet has opened a whole new world for web developers... Read More
What to do if you are an artist after you... Read More
In the big, wide online world there are millions of... Read More
1. Address your targeted audience on your business site. Example:... Read More
It is an undeniable fact that not everybody is keen... Read More
Designing and creating your own website does not have to... Read More
I'm a freelance programmer and somehow I managed to get... Read More
There are hundreds of millions of Web surfers today. Each... Read More
Is your website Really useful?I had a 'rep' in yesterday... Read More
Recently, a friend asked "What's the deal with those DIY... Read More
1) Word of Mouth The single most powerful form of... Read More
Build it and they will come is not always true;... Read More
Yahoo has long offered email, an online calendar, notes, bookmarks,... Read More
When we review the sites of potential clients, there are... Read More
Dynamically Update Your Web Pages Via E-MailIf you can Send... Read More
In the late 1990's three San Francisco based web developers... Read More
Visitors to your site come looking for information or solutions... Read More
Just like all things in life, the ways to run... Read More
So you have decided that you want to do freelance... Read More
When building a relationship, listening is more important than talking.A... Read More
When a user signs up at your website, you may... Read More
O'Hare Chicago prom limo ..Is Your Web Site an Expense or an Investment?Why don't... Read More
The growth in Internet usage around the world is astounding... Read More
If you were asked to put a value on your... Read More
When people think about the Internet, they think about technology.... Read More
"Build it and they will come."--Filed of Dreams (1989) If... Read More
A while ago one of my clients approached me and... Read More
You've decided to create a website to market your products... Read More
1. The first page appears quickly.It's a good way to... Read More
The Disability Discrimination Act states that service providers must not... Read More
Let's begin by setting some limits. If you're like me,... Read More
No matter the size of your business, having a web... Read More
Revenues are often lost because many business owners don't see... Read More
One of the things that many people overlook when building... Read More
With the New Year upon us yet again, it's time... Read More
In the late 1990's three San Francisco based web developers... Read More
In about the Time it takes to Watch a Reality... Read More
There are lots of HTML editors on the market, however,... Read More
Many websites I come across don't have a single link... Read More
Losing website sales and traffic is sometimes simply a case... Read More
With search engines putting a damper on direct reciprocal links,... Read More
A lot has changed in the way sites are optimized... Read More
Here's something you may never have thought of before:If I... Read More
Many executives and investors are skeptical that software products can... Read More
The Internet is being used by local service business to... Read More
Website, website, website, everyone says you need one. But do... Read More
Web Development |