Image compression using an interger reversible wavelet transform with a property of precision preservation
A wavelet-based image compression system and method are presented. Compression is accomplished by performing a wavelet transformation of an input digital image. The resulting wavelet coefficients are compared to a threshold value. Coefficients falling below the threshold are discarded. The remaining coefficients are quantized. The quantized coefficients are then compressed using an entropy encoding technique, such as arithmetic, run length, or Huffman encoding, or a combination of Huffman and run length encoding. The wavelet transform can be an integer wavelet transform derived using a lifting scheme or correction method, while the quantization scheme can be sub-band oriented. Input color image pixels can be reduced using a color table. In addition, color pixels can be transformed between color spaces prior to wavelet transformation.
1. A method of compressing a data file having data elements each represented by a number of bits, comprising:
performing a wavelet transformation of the data file using modular arithmetic to provide a series of wavelet coefficients, each of said coefficients being represented by a number of bits having a maximum count no greater than a number of bits representing each of said data elements;
discarding wavelet coefficients that fall below a predetermined threshold value;
quantizing remaining wavelet coefficients to provide a quantized series of wavelet coefficients; and
compressing the quantized series of wavelet coefficients to provide a compressed data file.
2. The method of claim 1 wherein the compressing step comprises the step of applying an entropy coding to the quantized series of wavelet coefficients.
3. The method of claim 2 wherein the entropy coding is selected from the group of arithmetic, Huffman, run length and Huffman run length combined.
4. The method of claim 2 further comprising the step of performing a color transformation of the data file prior to the wavelet transformation step.
5. The method of claim 4 wherein the quantizing step comprises sub-band orientation quantization.
6. The method of claim 5 wherein the wavelet transformation step comprises integer wavelet transformation.
7. The method of claim 6 wherein the integer wavelet transformation comprises biorthogonal filter method.
8. The method of claim 6 wherein the integer wavelet transformation comprises the correction method.
9. A program for compressing a data file having data elements each represented by a number of bits, comprising:
a routine for performing a wavelet transformation of the data file using modular arithmetic to provide a series of wavelet coefficients, each of said coefficients being represented by a number of bits having a maximum count no greater than a number of bits representing each of said data elements;
a routine for quantizing those wavelet coefficients which fall above a predetermined threshold value to provide a quantized series of wavelet coefficients; and
a routine for compressing the quantized series of wavelet coefficients to provide a compressed data file.