The 8 bit-planes of a gray-scale image (the one on left)

This article is about the digital information term. For the company, see Bitplane.

A bit plane of a digital discrete signal (such as image or sound) is a set of bits having the same position in the respective binary numbers^[1].

For example, for 16-bit data representation there are 16 bit-planes: the first bit-plane contains the set of the most significant bit and the 16th contains the least significant bit.

It is possible to see that the first bit-plane gives the roughest but the most critical approximation of values of a medium, and the higher the number of the bit plane, the less is its contribution to the final stage. Thus, adding bit-plane gives a better approximation.

Incrementing a bit plane by 1 gives the final result half of a value of a previous bit-plane. If a bit is set to 1, the half value of a previous bit-plane is added, otherwise it does not, defining the final value.

Bitplane is sometimes used as synonymous to Bitmap; however, technically the former refers to the location of the data in memory and the latter to the data itself.^[2]

One aspect of using bit-planes is determining whether a bit-plane is random noise or contains significant information.

One method for calculating this is compare each pixel (X,Y) to three adjacent pixels (X-1,Y), (X,Y-1) and (X-1,Y-1). If the pixel is the same as at least two of the three adjacent pixels, it is not noise. A noisy bit-plane will have 49% to 51% pixels that are noise.^[3]

[edit] Applications

As an example, in PCM sound encoding the first bit in sample denotes the sign of the function, or in the other words defines the half of the whole amplitude values range, and the last bit defines the precise value. Replacement of more significant bits result in more distortion than replacement of less significant bits. In lossy media compression that uses bit-planes it gives more freedom to encode less significant bit-planes and it is more critical to preserve the more significant ones^[4].

As illustrated in the image above, the early bitplanes, particularly the first, may have constant runs of bits, and thus can be efficiently encoded by run-length encoding. This is done (in the transform domain) in the Progressive Graphics File image format, for instance.

[edit] Programs

Many image processing packages can split an image into bit-planes. Open source tools such as Pamarith from Netpbm and Convert from ImageMagick can be used to generate bit-planes.

[edit] See also

• Color depth
• Planar
• Binary image

[edit] References

1. ^ "Bit Plane". PC Magazine. http://www.pcmag.com/encyclopedia_term/0,2542,t=bit+plane&i=38689,00.asp. Retrieved 2007-05-02. 
2. ^ "Bit Plane". FOLDOC. http://foldoc.org/foldoc.cgi?bit+plane. Retrieved 2007-05-02. 
3. ^ Strutz, Tilo (2001). "Fast Noise Suppression for Lossless Image Coding". Proceedings of Picture Coding Symposium (PCS'2001), Seoul, Korea. http://citeseer.ist.psu.edu/strutz01fast.html. Retrieved 2008-01-15. 
4. ^ Cho, Chuan-Yu; Chen, Hong-Sheng; Wang, Jia-Shung (2005-07). "Smooth Quality Streaming With Bit-Plane Labelling" (abstract). Visual Communications and Image Processing (The International Society for Optical Engineering) 5690: 2184–2195. doi:10.1117/12.633501. http://adsabs.harvard.edu/abs/2005SPIE.5960.2184C. Retrieved 2007-05-02.