US 12,262,057 B2
Method and apparatus of image compression with bit rate control
Hsu-Jung Tung, HsinChu (TW); Chi-Wang Chai, San Jose, CA (US); Weimin Zeng, San Jose, CA (US); and Yi-Chen Tseng, HsinChu (TW)
Assigned to Realtek Semiconductor Corp., HsinChu (TW)
Filed by Realtek Semiconductor Corp., HsinChu (TW)
Filed on Mar. 22, 2022, as Appl. No. 17/701,647.
Prior Publication US 2023/0308687 A1, Sep. 28, 2023
Int. Cl. H04N 19/625 (2014.01); H04N 19/176 (2014.01)
CPC H04N 19/625 (2014.11) [H04N 19/176 (2014.11)] 14 Claims
OG exemplary drawing
 
1. A method for compressing images based on joint photographic experts group (JPEG) standard, comprising:
compressing data of one or more first image blocks with a first compression level to produce compression data of the one or more first image blocks;
adjusting the first compression level to obtain a second compression level according to at least one of a data size-related index regarding the compression data of the one or more first image blocks or a transmission-related index regarding transmission of the compression data of the one or more first image blocks; and
compressing data of a second image block with the second compression level, comprising:
converting the data of the second image block into a plurality of discrete cosine transform (DCT) coefficients;
quantizing the plurality of DCT coefficients of the second image block by applying a quantization table to obtain a plurality of quantized DCT coefficients of the second image block; and
producing compression data of the second image block by encoding based on the quantized DCT coefficients of the second image block, comprising:
reducing values of only a subset of the plurality of quantized DCT coefficients of the second image block to obtain at least one value-reduced quantized DCT coefficient through direct value adjustment rather than through quantization table adjustment if the second compression level is higher than the first compression level; and
producing the compression data of the second image block by encoding the at least one value-reduced quantized DCT coefficient and non-value-reduced quantized DCT coefficients.