Image compression
The invention provides methods that improve image compression and/or quality within the JPEG process by using a low-pass filter to remove high frequency components from image data, which removes blocking artifacts. Preferred embodiments apply the low-pass filter to the Chroma components after decompression prior to conversion into RGB color space.
1. A method for processing image data, the method comprising:
receiving an original image;
transforming the original image into the YCbCr color space to produce a YCbCr image;
performing a discrete cosine transform (DCT) of the YCbCr image to obtain DCT coefficients;
applying a low pass filter to Chroma components of the DCT coefficients while allowing a Luma component to pass unfiltered;
quantizing the filtered DCT coefficients to yield quantized, filtered DCT coefficients; and
compressing the quantized, filtered DCT coefficients to produce a JPEG compressed image.
2. The method of claim 1 , further comprising:
decoding the JPEG compressed image to produce a YCbCr image; and
transforming the filtered YCbCr image into the RGB color space to produce an output image.
3. The method of claim 1 , wherein the low-pass filter is applied prior to the quantizing.
4. The method of claim 3 , further comprising blocking the YCbCr image into blocks of pixels.
5. The method of claim 3 , wherein the DCT is a type-II DCT.
6. The method of claim 3 , wherein quantizing the DCT coefficients includes scaling the DCT coefficients and rounding the scaled DCT coefficients to the nearest integers.
7. The method of claim 3 , wherein compressing the quantized, filtered DCT coefficients uses entropy encoding to create the JPEG compressed image.
8. The method of claim 7 , wherein entropy coding includes Huffman coding or run length encoding.
9. The method of claim 7 , wherein the steps are performed on a camera comprising a processor coupled to a non-transitory memory device.
10. The method of claim 7 , further comprising writing the JPEG compressed image to tangible memory.
11. The method of claim 1 , wherein the low pass filter removes one or more blocking artifacts from the output image.
12. A method for compressing image data, wherein the method consists of:
performing a discrete cosine transform (DCT) on YCbCr image data to return DCT coefficients;
applying a low pass filter to Chroma components of the DCT coefficients while allowing a Luma component to pass unfiltered;
quantizing the filtered DCT coefficients to return quantized, filtered DCT coefficients;
compressing the quantized, filtered DCT coefficients to produce compressed image data; and
writing the compressed image data to tangible memory.
13. The method of claim 12 , wherein the steps are performed on a camera comprising a processor coupled to a non-transitory memory device.
14. The method of claim 13 , wherein compressing the quantized, filtered DCT coefficients comprises Huffman coding.