How to remove the high frequency DCT coefficients without losing the image dimensions ?

Im in stuck in this part of my code, after applying the DCT on the image, I set the coefficients that have energy lower than 5 to zero , then i applied zigzag, now i want to choose only the first strong cooefficients that have high energy, the question is how to do this? since the way i tried gave me horrible result, It gave me only a quarter of the image as an output after idct2, Can you help me please to solve this ? I need to choose only the highest energy coefficients without losing the original image dimensions, is there a way?

<< input:

output:

I = imread('process/13.jpg');
figure;
imshow(I);
 J = blkproc(I,[64 64],'dct2');
 figure
 imshow(J);

imshow(log(abs(J)),[]), colormap(jet), colorbar
J(abs(J) < 5) = 0;
%B=J;
%B(1:1) = 0;

   fun=zigzag(J);
   B3=fun(1:10000);
   A=imresize(B3,[100,100]);
   [M N]=size(A);
   in1=izigzag(B3,M,N);
  J2 = blkproc(in1,[64 64],'idct2');
  figure
  imshow(J2,[0 255]);
  figure
  imshow(log(abs(J2)),[]), colormap(jet), colorbar

%zigzag%

function output = zigzag(in)

% initializing the variables
%----------------------------------
h = 1;
v = 1;

vmin = 1;
hmin = 1;

vmax = size(in, 1);
hmax = size(in, 2);

i = 1;

output = zeros(1, vmax * hmax);
%----------------------------------

while ((v <= vmax) & (h <= hmax))

      if (mod(h + v, 2) == 0)                 % going up

          if (v == vmin)       
              output(i) = in(v, h);        % if we got to the first line

              if (h == hmax)
          v = v + 1;
        else
                h = h + 1;
              end;

              i = i + 1;

          elseif ((h == hmax) & (v < vmax))   % if we got to the last column
              output(i) = in(v, h);
              v = v + 1;
              i = i + 1;

          elseif ((v > vmin) & (h < hmax))    % all other cases
              output(i) = in(v, h);
              v = v - 1;
              h = h + 1;
              i = i + 1;
       end;

      else                                    % going down

         if ((v == vmax) & (h <= hmax))       % if we got to the last line
              output(i) = in(v, h);
              h = h + 1;
              i = i + 1;

         elseif (h == hmin)                   % if we got to the first column
              output(i) = in(v, h);

              if (v == vmax)
          h = h + 1;
        else
                v = v + 1;
              end;

              i = i + 1;

         elseif ((v < vmax) & (h > hmin))     % all other cases
              output(i) = in(v, h);
              v = v + 1;
              h = h - 1;
              i = i + 1;
          end;

      end;

      if ((v == vmax) & (h == hmax))          % bottom right element
          output(i) = in(v, h);
          break
      end;

end;

%inv zigzag%

function output = izigzag(in, vmax, hmax)

% initializing the variables
%----------------------------------
h = 1;
v = 1;

vmin = 1;
hmin = 1;

output = zeros(vmax, hmax);

i = 1;
%----------------------------------

while ((v <= vmax) & (h <= hmax))

      if (mod(h + v, 2) == 0)                % going up

          if (v == vmin)
              output(v, h) = in(i);

              if (h == hmax)
          v = v + 1;
        else
                h = h + 1;
              end;

              i = i + 1;

          elseif ((h == hmax) & (v < vmax))
              output(v, h) = in(i);
              i;
              v = v + 1;
              i = i + 1;

          elseif ((v > vmin) & (h < hmax))
              output(v, h) = in(i);
              v = v - 1;
              h = h + 1;
              i = i + 1;
          end;

      else                                   % going down

         if ((v == vmax) & (h <= hmax))
              output(v, h) = in(i);
              h = h + 1;
              i = i + 1;

         elseif (h == hmin)
              output(v, h) = in(i);

              if (v == vmax)
          h = h + 1;
        else
                v = v + 1;
              end;

              i = i + 1;

         elseif ((v < vmax) & (h > hmin))
              output(v, h) = in(i);
              v = v + 1;
              h = h - 1;
              i = i + 1;
          end;

      end;

      if ((v == vmax) & (h == hmax))
          output(v, h) = in(i);
          break
      end;

end;