Frequently asked questions

Here you can find a selection of answered questions. If you have a question not on this page, just send a mail. We try to answer as quickly as possible.

• Where is the information stored?
• Can the embedded information get lost?
• Why are the coded images stored only as "PNG" files?
• Why is the quality of embedded images so bad?
• Can coded images also be included in Web pages?
• Is Smage freeware?

Where is the information stored?

The information is stored as digital watermarks in those regions of the image it is associated with. To this end, the colors of the image are slightly modified, which is invisible to the naked eye.

Can the embedded information get lost?

Yes. Once the geometry of the image is modified (e.g., resizing the image) or the colors of the image are however changed, the encoded information cannot be exactly recovered. The same applies when the coded image is converted into another file format by which the image is lossy compressed (e.g., conversion to "JPEG").

Why are the coded images stored only as "PNG" files?

The coded image may not be stored by a technique that applies lossy compression such as "JPEG". The "PNG" file format allows to compress and store an image without loss. In addition, the "PNG" file format is widely-used.

Why is the quality of embedded images so bad?

Before embedding an image into the original image, it is converted into an indexed format. That means the RGB values at each pixel position are replaced by pointers into a color table which can include only 256 RGB color values. This is necessary because the required storage space of RGB images is larger than a region within the original image can provide. Currently, the internal conversion from RGB to indexed is not optimally implemented in Smage. Hence, we recommend to convert the image to an indexed format prior to its embedding into the original image using an external image processing program (e.g., Gimp).

Can coded images also be included in Web pages?

Yes. Here is described how it works. To actually visualize the information encoded in an image, a Web browser plugin must be installed, which normally happens during the setup of Smage.

Is Smage freeware?

Yes. The program "Smage" as well as the included class library "libSmage" are freely available (according to the GNU General Public License), as long as they are not used commercially.