Pre-Allocate Space for a Cell Array

I'm working with confocal microscopy images. Specifically Z-stacks. I want to manipulate the images. However, I'm having a problem preallocating the space in memory.

%Open Image
bfopen()

%Extract Image Data
image_data=ans{1,1};

%Create an Array focused on the pixel_data
pixel_data=image_data(:,1);

%Ask User How Many Laser Channels were used to Acquire the Image
total_laser_channels=input('How many laser channels were used to acquire this image?\n');

%Determine the number of image slices in each channel
images_per_channel=length(pixel_data)/total_laser_channels;

*

%Preallocate space and variables for each channel
  if total_laser_channels==1
      channel1{images_per_channel,:}=[];
  elseif total_laser_channels==2
      channel1{images_per_channel,:}=[];
      channel2{images_per_channel,:}=[];
  elseif total_laser_channels==3
      channel1{images_per_channel,:}=[];
      channel2{images_per_channel,:}=[];
      channel3{images_per_channel,:}=[];
  elseif total_laser_channels==4
      channel1{images_per_channel,:}=[];
      channel2{images_per_channel,:}=[];
      channel3{images_per_channel,:}=[];
      channel4{images_per_channel,:}=[];
  elseif total_laser_channels==5
      channel1{images_per_channel,:}=[];
      channel2{images_per_channel,:}=[];
      channel3{images_per_channel,:}=[];
      channel4{images_per_channel,:}=[];
      channel5{images_per_channel,:}=[];
  else
      break
  end*

%Loop: Each laser channel has corresponding images
i=1;
while i<length(pixel_data)+1
    if total_laser_channels==1
        channel1=[channel1;pixel_data(i,1)];
        i=i+1;
    elseif total_laser_channels==2
        channel1=[channel1;pixel_data(i,1)];
        channel2=[channel2;pixel_data(i+1,1)];
        i=i+2;
    elseif total_laser_channels==3
        channel1=[channel1;pixel_data(i,1)];
        channel2=[channel2;pixel_data(i+1,1)];
        channel3=[channel3;pixel_data(i+2,1)];
        i=i+3;
    elseif total_laser_channels==4
        channel1=[channel1;pixel_data(i,1)];
        channel2=[channel2;pixel_data(i+1,1)];
        channel3=[channel3;pixel_data(i+2,1)];
        channel4=[channel4;pixel_data(i+3,1)];
        i=i+4;
    elseif total_laser_channels==5
        channel1=[channel1;pixel_data(i,1)];
        channel2=[channel2;pixel_data(i+1,1)];
        channel3=[channel3;pixel_data(i+2,1)];
        channel4=[channel4;pixel_data(i+3,1)];
        channel5=[channel5;pixel_data(i+4,1)];
        i=i+5;
    else
        display('Too many or wrong number of laser channels.')
        break
    end
end

For the images i'm looking at now the total_laser_channels is 3. images_per_channel is 45. However for channel1, channel2, channel3 after i run the code i get a 46x1 array instead of the 45x1 array that i want.

[]

2048x2048 uint16

2048x2048 uint16

2048x2048 uint16

2048x2048 uint16

2048x2048 uint16

2048x2048 uint16

2048x2048 uint16....

The first position of the cell array has []

Any help would be greatly appreciated.

[Ben11]

Maybe you could use a switch/case and a for loop? On a side note if you want to remove the empty array from your cell array you can use ths:

channel1 = channel1(~cellfun('isempty', channel1));

Answer 1

[Prateekshya]

Hello Jessica,

This error is occuring because of empty array initialization. Instead of initializing the cell arrays with empty arrays, try preallocating them with the correct size and directly assign some data. Here is an example how to do it:

channel1 = cell(images_per_channel, 1);

This will avoid unnecessary allocation and resizing of the arrays.

I hope this helps!