Transparent Images in the Gadget
The images used in a gadget window have a shadow effect and sometimes semitransparent oval shapes. These images use either a PNG or a GIF image format. The recommended images used for the gadget are in a PNG format. The next few sections describes these formats in more detail.
Microsoft started supporting PNG icons with alpha transparency in Windows Vista. Creating an alpha transparent image is a process of combining two images: a central image laid on top of a background image to create an appearance of partial transparency. It is used to display an image that has transparent or semitransparent pixels.
Alpha transparency is used extensively in the images used for gadgets to create the shadow or oval shape effect.
Portable Network Graphics File
PNG is an abbreviation for Portable Network Graphics. It's an advanced graphics format with 48-bit color. It's one of the standard formats that is beginning to replace the use of GIF images, which are limited to 8-bit colors (256 colors). It also includes an alpha channel for showing transparency.
This is the standard format used in all the images for a gadget. A PNG file allows every pixel (dot) to have any level of transparency, from completely opaque to completely transparent and anything in between.
The PNG image format combines the best features of GIF and JPG/JPEG. It supports binary transparency along with alpha transparency, meaning that each pixel of the image can also have one of 256 different levels of transparency. PNG format produces a file with approximately the same file size as that of an equivalent GIF image, assuming that they have the same number of colors. Appendix A shows how to create a PNG image in Adobe Photoshop.
GIF File Limitations
Graphics Interchange Format is a popular bitmapped graphics file format developed by CompuServe. To date, it is the most widely used graphics format on the Web. Given that GIF files can also be transparent, you might wonder why you would not want to use them in favor of PNG. There are three reasons for not using a GIF format:
- GIF files support only 100% transparency; you cannot create a translucent shadow effect.
- GIF images are limited to 8-bit colors, so they're not very rich.
- PNG format is endorsed by the World Wide Web Consortium (W3C), an organization responsible for managing standards for the World Wide Web.