Are DC coefficients included in every block of a compressed JPEG without exception?

Asked Oct 26 '17 at 15:17

Active Oct 30 '17 at 10:36

Viewed 184 times

I am reading a compressed JPEG bitstream bitwise to locate the EOB markers.

After each EOB, I would expect to find a Huffman code representing the DC coefficient bit-size.

In the vast majority of cases this I have found this to be true, but occasionally there will be a long (~10 bit) string of 1's followed by a similar string of 0's after an EOB. No DC Huffman code defined in the DHT of the image produces a match. Is it possible that this block has no DC coefficient? Why would this be the case? If not, is there another explanation?

Assuming I am right in thinking that all markers are byte-aligned, there are no restart markers in the image. All bytes with a value of 255 are followed by a zero once the scan has started.

edited Oct 30 '17 at 10:36

asked Oct 26 '17 at 15:17

Mike H

1

Is it a restart marker? – harold Oct 27 '17 at 11:16
I depends upon the type of frame. – user3344003 Oct 27 '17 at 18:09
@user3344003 Would you mind elaborating on this? I can't find any literature regarding this issue. – Mike H Oct 30 '17 at 11:52
In a progressive frame,DC and AC coefficients are encoded separately. – user3344003 Oct 31 '17 at 00:37
@user3344003 How can it be determined whether the jpeg is compressed sequentially or progressively? The fact that my technique has worked for the majority of the time would perhaps suggest to me that it is sequential – Mike H Oct 31 '17 at 09:00
From the SOF marker. – user3344003 Oct 31 '17 at 14:39

Are DC coefficients included in every block of a compressed JPEG without exception?

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