MagiCompression is a technology for automatically compressing JPEGs by more than the standard amount.
MagiCompression takes advantage of the fact that not all parts of an image are as important as others and can be compressed more than other parts without much noticeable difference. The benefits vary from image to image but typically the extra compression achieved is 1.5 – 2x. The MagiCompression algorithm scans your images looking for regions of high detail and preserves them while compressing areas of less detail much more.
If you are in a hurry or have a lot of images to compress you may want to rely on the MagiCompress algorithm with no human intervention.
If you have time or the size of your image is very important, eg it might be on your home page or be a banner advert, you can help the algorithm by fine tuning regions where you think your human eye can do a better job.
Image Optimizer provides you with all the tools you need for both cases.
MagiCompress 2 is an improved algorithm that works well with imperfect images e.g. images with noise or blurred images. With MagiCompress 2 you may find you can push the MagiCompression slider to as far as 80 or 90% without noticeable harm to the image. MagiCompress 2 is more sensitive to color changes and is better for thumbnails.
Extra Compression is used to compress a JPEG image with more than standard JPEG compression and in such a way that the extra compression may be removed in parts of the image. It is similar to MagiCompression but it does not vary with the image content i.e. it is a constant level across the image. Normally MagiCompression works better than Extra Compression but sometimes you may want to compress some regions regardless of what is in the image in that region. In these cases you can use Extra compression. (see Compress Image Control palette)
Dithering is used to simulate colors not available in the palette of a GIF or PNG image. This is done by creating a fine pattern of pixels of available colors from the palette.
You should use dithering if the image you are compressing contains photographic regions or regions with many colors or smooth gradients to improve the look of these regions.
Dithering will almost always make your images larger so you should us it sparingly
You can use regional dithering to add dithering only in the regions that need it.
See Image Optimizer technology for more information about dithering.
Smoothing is used to smooth out noise and roughness in an image.
If you are reading in a GIF you may find it useful to smooth regions of an image that have been dithered by another program (but note it is always better to start with the original true color image if you have it). Smoothing will remove the dithering noise.
Smoothing removes detail in an image so you can use it on JPEG images to remove detail and make the JPEG smaller. It works a bit like extra compression. Normally MagiCompression or Extra Compression will give you better results.