OTA Bitmap is used as a part of the following Smart Messaging formats: Operator logo, CLI icon, Picture Message and Downloadable Profile. In today's Nokia phones the maximum size of the operator logo and the CLI icon is 72x14 pixels, while the maximum size of the picture message and the screen saver is 72x28 pixels.
The OTA Bitmap syntax can be found in Smart Messaging specification. An OTA Bitmap consists of a bitmap header and a bitmap data. The size of the bitmap is specified in the header. Several other information (ie. number of colors) are also defined there, but those informations handle issues that are not supported in today's Nokia phones. So these values are similar in all OTA Bitmap headers.
Typical OTA Bitmap (72x14 pixels) header is: 00480E01
48 'Width of the bitmap is 72 pixels'
0E 'Height of the bitmap is 14 pixels'
01 'Number of colors or grey shades (only one color)'
The image data is located after the header information and is encoded as follows. Each semi-octet in the OTA bitmap presents 4 pixels in the original bitmap. Because one row takes 18 semi-octets, the whole 72x14 size (operator logo and CLI icon) bitmap takes 18x14 = 252 semi-octets = 126 octets. In the case of the picture message and screen saver the whole 72x28 size bitmap takes 18x28 = 504 semi-octets = 252 octets.
For example, if the first four pixels of the image are 1010 (1 - black, 0 - white), the first semi-octet of the OTA bitmap data is hex A.
This is an example of a simple OTA bitmap (72x14 pixels). In the picture, there are two black lines and several black dots.
FFFFFFFFFFFFFFFFFF <- First line black
000000000000000000 <- Second line white
10F000000000000000 <- Fourth pixel of this line is
000000000000000000 black and 9-12 pixels are
000000000000000000 also black
000000000000000001 <- Last pixel of this row/bitmap is black
For more information, please refer to the Smart Messaging Specification 3.0.0. or later