FAQ Database Discussion Community


Using key positions in steganography using DCT

image,image-processing,dct
I have a question about steganography. Once the DCT matrix's are computed and the LSB's are replaced can we assume that the location at which the data is entered in the DCT of the cover image is know at the receiver? If not then how is the image reconstructed?

─░mage Dividing in C for DCT

c,image,divide,dct
Can anyone please tell us how to divide the image into 8X8 blocks? I can read the image, but not divide it into an 8x8 submatrix for DCT. int main() { FILE *image_raw; unsigned char **matriz_image; int i, j; int rows=1080, colums=1920; matriz_image = (unsigned char **) malloc (rows*sizeof(unsigned char...

Discrete cosine Transform (DCT) in java

java,arrays,dct
This is the sourcecode DCT .. !!! unknown array of 4x4 DCT will be done by splitting the 4x4 array into several blocks past yyang 2x2 transformation on each block ... !!! I want to ask, how to display an array that has been done, but with size 4x4 transformation,...

Overlapping sliding window over an image using blockproc or im2col?

image,matlab,image-processing,image-segmentation,dct
I have to apply dct2 to small windows of my image, preferably by using an overlapping window. I have found out that there are two functions in Matlab that can make this possible blockproc and im2col. I am having trouble understanding either and would appreciate some clarification. blockproc can be...

Warning: IMSHOW(I,N) is an obsolete syntax. Your grayscale image will be displayed using 256 shades of gray

matlab,image-processing,dct
I get this warning:Warning: IMSHOW(I,N) is an obsolete syntax. Your grayscale image will be displayed using 256 shades of gray..please help me. Ihave implemented 2d dct.why its not working for m=64; m=input('enter the basis matrix dimension:'); n=m; alpha2=ones(1,n)*sqrt(2/n); alpha2(1)=sqrt(1/n); alpha1=ones(1,m)*sqrt(2/m); alpha1(1)=sqrt(1/m); for u=0:m-1 for v=0:n-1 for x=0:m-1 for y=0:n-1 a(u+1,v+1,x+1,y+1)=alpha1(u+1)*alpha2(v+1)*cos((2*x+1)*u*pi/(2*n))*cos((2*y+1)*v*pi/(2*n));...

where is the DCT matrix in Libjpeg?

image-processing,jpeg,libjpeg,dct
In libjpeg I am unable to locate the 8x8 DCT matrix ? If I am not wrong this matrix is always a constant for a 8x8 block . it must contain 1/sqrt(8) on the first row but where is this matrix ?

How to get DCT-coefficients from Jpeg using Visual C# and LibJpeg.Net

c#,jpeg,dct
I need to get DCT-coefficients array after quantization for further changing bits (steganography). My question is: Lets say, i have jpeg image in picturebox or whatever. How can i acess to dct coef. of this image using C# and library like LibJpeg.Net? Need a code pls. Can't find anything complete...