how do I do DCT on a 100x100 image?

huhua wrote:
> 
> "jim" <"sjedgingN0sp"@m@mwt.net> wrote in message
> news:1212070084_3372@isp.n...
> >
> >
> > huhua wrote:
> >>
> >> "bharat pathak" <bharat@arithos.com> wrote in message
> >> news:x-ydnb2qdvrRjKPVnZ2dnUVZ_srinZ2d@giganews.com...
> >> > matlab has a function called dct2
> >> > use it.
> >> >
> >> > bharat pathak
> >> >
> >> > arithos designs
> >> > www.Arithos.com
> >> >
> >>
> >> Do I need to cut the 100 x 100 image into 8x8 first?
> >
> > If you want to go from 100X100 to 10X10 you need to make each DCT
> > transform 10X10 (instead of 8X8). Then when you have 100 transforms
> > results with 100 frequency elements in each. Then you need iterate thru
> > the 100 elements in each by discarding and quantizing some or all. Usually
> > the scheme for doing that affects the higher frequencies the most the
> > lower frequencies less and usually leaves the DC element alone). That is
> > the lossy part. After that you get data reduction by standard data
> > compression techniques which are usually lossless.
> > In other words,  if you do the quantization and/or discarding part as
> > just zeroing bits you will after doing that have the same size data as the
> > original (with a lot of bits zeroed). If you then run that data thru a
> > typical compression scheme (e.g. zip it) you will get much greater data
> > reduction than just compressing the original. Or you can create your own
> > compression scheme based on your knowledge of where the data is dense and
> > where it is sparse.
> > To reverse the process you would uncompress (e.g. unzip) and then do the
> > inverse transform.
> >
> > -jim
> >
> 
> Is it possible to run 2D DCT on my 100x100 image directly and select the
> top-left panel (approx. 10x100) which are the dominating ones and neglect
> the rest?

	 I don't know what problem you are trying to solve so it's difficult make
suggestions on how to perfect your solution. 
	If you are just trying to develop a compression algorithm, You shouldn't
need to worry about where the image has the most information. Areas that
are blank won't take up much storage space once it is compressed.

-jim


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