Re: how do I do DCT on a 100x100 image?
- From: jim <"sjedgingN0sp"@m@xxxxxxx>
- Date: Fri, 30 May 2008 19:43:27 -0500
huhua wrote:
"jim" <"sjedgingN0sp"@m@xxxxxxx> wrote in message
news:1212070084_3372@xxxxxxxx
huhua wrote:
"bharat pathak" <bharat@xxxxxxxxxxx> wrote in message
news:x-ydnb2qdvrRjKPVnZ2dnUVZ_srinZ2d@xxxxxxxxxxxxxxx
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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