FFT of a Block processed image.

Hello, I am trying to do FFT on each block of a block processed image. All I have now is the block processed image that works fine but I would like to apply FFT to each block. Can anyone help?

CODE:

Image = imread("Kobe.jpg");
[Image_Height,Image_Width,Number_Of_Colour_Channels] = size(Image);

Block_Size = 50;
Number_Of_Blocks_Vertically = floor(Image_Height/Block_Size);
Number_Of_Blocks_Horizontally = floor(Image_Width/Block_Size);
Image_Blocks = struct('Blocks',[]);

Index = 1;
for Row = 1: +Block_Size: Number_Of_Blocks_Vertically*Block_Size
    for Column = 1: +Block_Size: Number_Of_Blocks_Horizontally*Block_Size
        
    Row_End = Row + Block_Size - 1;
    Column_End = Column + Block_Size - 1;
        
    if Row_End > Image_Height
       Row_End = Image_Height;
    end
    
    if Column_End > Image_Width
       Column_End = Image_Width;
    end
    Temporary_Tile = Image(Row:Row_End,Column:Column_End,:);
    
    %Storing blocks/tiles in structure for later use%
    Image_Blocks(Index).Blocks = Temporary_Tile;
    subplot(Number_Of_Blocks_Vertically,Number_Of_Blocks_Horizontally,Index); imshow(Temporary_Tile);
    Index = Index + 1;
    
    
    end  
end

Answer 1

[Matt J]

Using mat2tiles ( Download )

Image = imread("Kobe.jpg");

ImageTiles=mat2tiles(Image,[50,50]);

ImageTilesFFT = cellfun(@fft2,ImageTiles,'uni',0);

[Rai-Mond Davidson]

where do I place that piece of code in the code I provided, and would i need to modify anything in the code you sent?

[Matt J]

I gave you my idea of what the complete code should be.

[Rai-Mond Davidson]

Here's the error I get though:

Unrecognized function or variable 'mat2tiles'.

Error in Imageprocessing3 (line 6)

ImageTiles=mat2tiles(Image,[50,50]);

[Matt J]

That is almost certainly because you did not download mat2tiles from the link I gave you.

[Rai-Mond Davidson]

place this code:

Image = imread("Kobe.jpg");

ImageTiles=mat2tiles(Image,[50,50]);

ImageTilesFFT = cellfun(@fft2,ImageTiles,'uni',0);

After the function code or before?

[Matt J]

That's the whole thing! You can get rid of everything you originally had, except of course for

Image = imread("Kobe.jpg");

Answer 2

[Image Analyst]

You can just do

ft = fft(Temporary_Tile);

Then do with ft whatever you want to.

[omar Alharbi]

Hello Image Analyst,

If I would like to compute and plot the 2D frequency spectrum for multiple images, can I do that for each individual image and the avrege them? here is the code:

min=zeros;

min_1D=zeros;

for K = 1 :1500:75000

this_file = strcat('folder\frame',num2str(K),'.tif');

im_input = imread(this_file);

im_input = rgb2gray(im_input);

zfmin=fft2(im_input);

shiftmin=fftshift(zfmin);

min_2D=abs(shiftmin);

z_min=log10(min_2D);

min=min+z_min;

end

PSD_2D= (min)/ 50;

figure,

imagesc(PSD_2D)

colormap gray

1- is this a right way compute the spectrum?

2- If I would like to remove the DC component, I tried

zfmin= fft2(im_input-mean2((im_input))... do you recommend other way?

Thanks