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In digital signal processing, downsampling, compression, and decimation are terms associated with the process of resampling in a multi-rate digital signal processing system. Both downsampling and decimation can be synonymous with compression , or they can describe an entire process of bandwidth reduction ( filtering ) and sample-rate reduction.
More specific types of resampling include: upsampling or upscaling; downsampling, downscaling, or decimation; and interpolation. The term multi-rate digital signal processing is sometimes used to refer to systems that incorporate sample-rate conversion.
English: Each of 3 pairs of graphs depicts the spectral distributions of an oversampled function and the same function sampled at 1/3 the original rate. The bandwidth, B, in this example is just small enough that the slower sampling does not cause overlap (aliasing).
Decimation is the process of reducing sample rate. Decimation originally meant "take one sample in every 10", but later this term was generalized to simply mean any reduction in sample rate. This electronics-related article is a stub .
A mipmap is a prescaled set of downscaled copies. When downscaling, the nearest larger mipmap is used as the origin to ensure no scaling below the useful threshold of bilinear scaling. This algorithm is fast and easy to optimize. It is standard in many frameworks, such as OpenGL. The cost is using more image memory, exactly one-third more in ...
Lanczos windows for a = 1, 2, 3. Lanczos kernels for the cases a = 1, 2, and 3, with their frequency spectra. A sinc filter would have a cutoff at frequency 0.5. The effect of each input sample on the interpolated values is defined by the filter's reconstruction kernel L(x), called the Lanczos kernel.
Upsampling requires a lowpass filter after increasing the data rate, and downsampling requires a lowpass filter before decimation. Therefore, both operations can be accomplished by a single filter with the lower of the two cutoff frequencies.
DDCs are most commonly implemented in logic in field-programmable gate arrays or application-specific integrated circuits.While software implementations are also possible, operations in the DDS, multipliers and input stages of the lowpass filters all run at the sampling rate of the input data.