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Thread: JPEG Compression

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    JPEG Compression

    Hi,

    I'm new to the forum and have a question about JPEG compression. I coded the C-code from the JPEG software group version 8d released on 15/1/12, in Mathworks Simulink. When I run the code on a video sequence and look at the meta data for each compressed frame, saved as a jpeg file, some show Baseline DCT encoding and some Extended DCT encoding. I set the Encoding to the DCT_DEFAULT so I assumed that it would use the same encoding on all frames. There is very little difference in the image content when this switch occurs. Does anyone know why it switches bewteen the two and if so how do I stop it and force it to just use the baseline encoding?

    Thanks

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    Quote Originally Posted by elty View Post
    I'm new to the forum and have a question about JPEG compression. I coded the C-code from the JPEG software group version 8d released on 15/1/12, in Mathworks Simulink. When I run the code on a video sequence and look at the meta data for each compressed frame, saved as a jpeg file, some show Baseline DCT encoding and some Extended DCT encoding. I set the Encoding to the DCT_DEFAULT so I assumed that it would use the same encoding on all frames. There is very little difference in the image content when this switch occurs. Does anyone know why it switches bewteen the two and if so how do I stop it and force it to just use the baseline encoding?
    Baseline and extended Huffman modes only differ in so far as which quantization bucket sizes they allow and how many Huffman tables they allow. Entropy coding itself is exactly identical, so I wouldn't worry. The difference between these two "modes" is very minor and does not constitute a change in coding performance or coding model. BTW, "IJG" is not the "JPEG software group", and not related to JPEG. Official JPEG software can be found on www.jpeg.org, including reference implementations.

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    Smile Thanks

    Quote Originally Posted by thorfdbg View Post
    Baseline and extended Huffman modes only differ in so far as which quantization bucket sizes they allow and how many Huffman tables they allow. Entropy coding itself is exactly identical, so I wouldn't worry. The difference between these two "modes" is very minor and does not constitute a change in coding performance or coding model. BTW, "IJG" is not the "JPEG software group", and not related to JPEG. Official JPEG software can be found on www.jpeg.org, including reference implementations.
    Thanks

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