Re: I am Puzzled! How come my JPEG algorithm doesnt work?


Pete Fraser wrote:
"fulltime" <PiaoChieh@xxxxxxxxx> wrote in message
news:1166990841.574712.73920@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

==> so do u mean the deltas (DPM) might be causing the prob? taking the
-ve pixel value might be hazardous to the DCT o/p?

No. It should work fine if your DCT works OK. I was just thinking
you might get overflow depending on how you implemented it
(the diffs have twice the range of the pixels).

i am trying to see
if this algo will actually cut down on the bandwidth of the
transmission...

Quite unlikely. If you consider an 8x8 block with all the values the same,
either your diff scheme or DCT will result in something in the top left
corner of the block, and zeros everywhere else.
If you do your diff, then DCT, all output locations will be finite (I would
guess).

I been debugging my code, but i just cant see whats wrong with the
codes... If i perform normal JPEG, it works perfectly fine, but when i
include DPM, the image sucks big time...

just to check w u, after imread() the image, i convert from RGB to
YCbCr, after which, i perform the necessary DCT n Quant. Then i decode
n get back the pixels in 8*8 block. So i converted back to RGB and then
i do a uint8 to convert to 8 bit unsigned b4 displaying the image in
imshow(), is this way correct?

I don't know enough about your software.
Break it down. Use a monochrome image, and drop the quantization.
Look at the data after the idct and compare it with the data before
the dct.. If there are differences, find out why. And so on...

thks peter, u been of great help. Merry XMAS to u :p

You're welcome. Merry XMAS.

Hi Peter,

I don't know enough about your software.
Break it down. Use a monochrome image, and drop the quantization.
Look at the data after the idct and compare it with the data before
the dct.. If there are differences, find out why. And so on...
---> ya, i did try wat u mentioned, if not for the quantization,
everything works perfectly fine... so i guess we can conclude tat
quantization caused the error. Can i just say tat taking the delta of
the pixels will just not work since we definitely have to perform
quantization in the JPEG algo?

.