OTA Bitmap (Over The Air Bitmap) was a specification designed by Nokia for black and white images for mobile phones.

The OTA Bitmap was defined by Nokia as part of their Smart Messaging specification, to send pictures as a series of one or more concatenated SMS text messages. The format has a maximum size of 255x255 pixels. It is very rare for an OTA bitmap to measure anything other than 72x28 pixels (for Picture Messages) or 72x14/72x13 pixels (for Operator Logos). The specification contains a byte of data to be used for indicating a multicolour image. This was to future-proof the standard, but the advent of MMS meant it never got to implementation.

The OTA Bitmap format is a monochrome, uncompressed format using one bit per pixel. As the format was designed for cellular phones, there is no standard computer format. It may be stored as a binary file or as hex (usually without spaces) in a text file. Recognized extension is .otb.

Before the image itself there is a header. The header is four bytes wide. A typical example is: 00 48 1C 01. These are:

 00 The 'Infofield' (always remains as 00).
 48 The width of the bitmap, 72 pixels in this case (48 is hex for 72).
 1C The height of the bitmap, 28 pixels in this case (1C is hex for 28).
 01 The number of colours (always 1).

Other possibilities may be: 00 48 0E 01 (for 72x14 bitmaps), 00 48 0D 01 (for 72x13 bitmaps).

After the header the image itself starts. This example will use the following 72x28 pixel image.

The first 8 pixels, reading right from the top left hand corner are one white (0) followed by seven blacks (1111111), giving the first byte, in Binary, as 01111111.

Converting from the binary 01111111 to hex, results in the first byte that represents the pixels (7F). The next 8 characters are 8 blacks (11111111 or FF) and so on.

When all pixels from the top row are encoded, simply move to the next. There are no markers to indicate a new row, that information is contained in the header.

In the case of an OTA bitmap that is not a multiple of eight pixels in width, a single byte is used to convey information from two lines (e.g. two pixels from the first row and six from the second.) This is not the case in some other formats, so it is important to exercise care when converting between OTA and formats like WBMP.

Here is the result of the image converted to OTA.

00481C01//Header
7FFFEFFFEFFFFBFFFE//FirstRow
403FE8382FFFFBFFFE//SecondRow
483FA8382F9FFBFFFE//ThirdRow
4CFFA9FF2F8FFADADA//FourthRow
4EFF29012F80FA5252
5E7F69312FBF7B0706
4FFF69792FBEFB7776
47FF69792FBE7B0706
47FEEF7DEFBE7BFFFE
47FCEF7DE7BCF1FFFC
40F0EF7DE77CF1EDBC
21E7C9792798F1E53C
21E7C93927C8F1F07C
166F893923E6E0F778
152F888223F3E0F078
083F044443D7E0FFF8
043E022881EFC07FF0
023C013900FF803FE0
013800BA007F001FC0
00F0007C003E000F80
FFC00038001C0007FF
55FFFFFFFFFFFFFFAA
2AF387873F1E670F54
15F3939F3E4E2727A8
2AF3878F3E4E072754
55F3939F3E0E4727AA
FFF39B870E4E670FFF//PenultimateRow
00FFFFFFFFFFFFFF00//Last Row

• ImageMagick^[1]
• XnView (Not XnviewMP use legacy Xnview version) (as of version 1.97, Tools → Options → General → Display all image file types flag must be enabled, otherwise XnView will neither display nor save files of this format)

Note to review: there is no write support for OTA format in XnView

• Despite the image format calls OTA as the mentioned it above, image files can only be viewable if the file extension is ".otb" if you have any ota bitmap files, to view them first you could change its extensions to ".otb"
• File Viewer for Android This android app also read .otb files. App can be download from Google Play Store^[2]

• Operator logo

• Nokia Smart Messaging Specification v3.0.0

• Forum Nokia – Nokia Developer Website