Smush.It™ - Frequently Asked Questions (FAQ)

This page answers some of the most common questions we get about Smush.It.

Questions

• My GIF image file got converted to a PNG image file. Is this a bug?
• What will happen if I upload private images?
• Is there a Smush.it API I can access so that my images are automatically smushed when they are published?
• Are there any limitations on the image file size and type that I can smush?
• How does Smush.it handle the image copyright?
• Can I upload a folder to Smush.it containing image files to be smushed? Can you keep the directory structure in the downloadable zip file?
• What tools does Smush.it use to smush images?

Answers

My GIF image file got converted to a PNG image file. Is this a bug?

Smush.it converts GIF files to PNG files when the resulting PNG files are smaller. Converting GIF files to PNG files often produces substantial performance improvements. The PNG8 format is a palette (that is, indexed) image format, similar to the GIF format. PNG8 transparency is supported by all Grade-A browsers, including IE6. PNG8 file size is often much smaller than GIF file size.

Do not confuse the PNG8 format with truecolor PNG (also referred to as PNG24 or PNG32). The truecolor PNG format is not supported in IE6, and, if used, results in displays of gray squares instead of normal images.

Converting from GIF to PNG8 will require you to change file extensions in your CSS and HTML files.

What will happen if I upload private images?

When you use Smush.it from YSlow's Tools menu or Action column in the Components view, your web page's images are processed by the tool. We at Yahoo! are not particularly interested in what your images are, we just try to optimize them using our smushing techniques. However, the best policy is to keep your private images private and not upload them. We keep some statistics, such as total and average savings for the web pages Smush.it processes, in order to collect data that will help us improve our tools.

Note: Do not link to the smushed images on Smush.it since they will only be available there temporarily. Instead, download the zip file containing the smushed images for your web page and replace your image files with those files.

Is there a Smush.it API I can access so that my images are automatically smushed when they are published?

The API currently is not available for public use. We are working towards making this publicly accessible .

Are there any limitations on the image file size and type that I can smush?

Smush.it can process JPG, GIF, and PNG images that are up to one megabyte in size.

How does Smush.it handle the image copyright?

Yahoo! is committed to respecting the rights of owners of creative works. You may only use the Smush.it service to optimize images that you have the rights to modify or change. Many images that you may use on your site, especially those from feeds or image services, may have specific requirements regarding keeping certain portions of the metadata such as the copyright notice. You should ensure that you have satisfied these requirements before you optimize an image.

Smush.it currently keeps all JPG metadata and exif (exchangeable image file format) information. We are investigating how to leave the copyright field in place while removing the other metadata (for example: camera information, audio files, thumbnails, and so on).

Can I upload a folder to Smush.it containing image files to be smushed? Can you keep the directory structure in the downloadable zip file?

These features, along with the sortable table of results feature, are the most commonly requested upgrades to Smush.it. We are investigating how to implement these features. If you have suggestions or comments about this, please contact the Yahoo! Exceptional Performance group.

What tools does Smush.it use to smush images?

We have found many good tools for reducing image size. Often times these tools are specific to particular image formats and work much better in certain circumstances than others. To "smush" really means to try many different image reduction algorithms and figure out which one gives the best result.

These are the algorithms currently in use:

1. ImageMagick: to identify the image type and to convert GIF files to PNG files.
2. pngcrush: to strip unneeded chunks from PNGs. We are also experimenting with other PNG reduction tools such as pngout, optipng, pngrewrite. Hopefully these tools will provide improved optimization of PNG files.
3. jpegtran: to strip all metadata from JPEGs (currently disabled) and try progressive JPEGs.
4. gifsicle: to optimize GIF animations by stripping repeating pixels in different frames.

More information about the smushing process is available at the Optimize Images section of Best Practices for High Performance Web pages.

If there is an image reduction tool you think we should add to Smush.it, please post your suggestion to the Yahoo! Exceptional Performance group.