Convert 24 bit 2D array to 8 bit 3D (RGB) array

2 次查看（过去 30 天）
Oshin
Oshin 2012-3-27
Hello all,
I am reading in data from a camera sensor, and it is stored as a 32-bit 2D array. Here, the first 8 bits correspond to Red, the next 8 bits to Green, and so on. I want to split this 2D array (of size (a,b)) to a 3D array (a,b,3), where each element in the array is 8-bit long. I am currently doing this as follows:
[r c]= size(img);
IMG = zeros(r,c,3);
for i = 1:r
for j = 1:c
temp = dec2bin(img(i,j),24);
IMG(i,j,1) = bin2dec(fliplr(temp(1:8)));
IMG(i,j,2) = bin2dec(fliplr(temp(9:16)));
IMG(i,j,3) = bin2dec(fliplr(temp(17:24)));
end
end
figure, imshow(IMG(:,:,1))
figure, imshow(IMG(:,:,2))
figure, imshow(IMG(:,:,3))
This takes a very long time to compute (~ 20 minutes) for the large images that I am currently using.
Is there a more efficient way of doing this?
Thanks in advance!

请先登录，再回答此问题。

回答（2 个）

Walter Roberson
Walter Roberson 2012-3-27
IMGB = reshape( typecast(img, 'uint8'), [4, size(img)]);
Then row 1 will correspond to one of the bands, row 2 to another, etc..
You might need to do a bit of work to figure out which row is which.
  2 个评论
Jan
Jan 2012-3-27
If speed matters (does it ever?), James' typecast function is recommended: http://www.mathworks.com/matlabcentral/fileexchange/17476-typecast-and-typecastx-c-mex-functions
Geoff
Geoff 2012-3-27
Good point. I use MatLab for prototyping speed, not execution speed.

请先登录，再进行评论。

Geoff
Geoff 2012-3-27
Try using bitwise operators like you would in C. These handily operate on a matrix, so you can split out your components like so:
[r c]= size(img);
IMG = zeros(r,c,3);
IMG(:,:,1) = uint8(bitand(img, 255))
IMG(:,:,2) = uint8(bitand(bitshift(img,-8), 255));
IMG(:,:,3) = uint8(bitand(bitshift(img,-16), 255));
  3 个评论
显示 1更早的评论
Jan
Jan 2012-3-27
I assume that a division is faster than the bit-shifting.
Geoff
Geoff 2012-3-27
Well, I come from a C background so I just assumed that those functions share some kind of parallel. =) If division in MatLab is faster, that doesn't say much about the bitshift function!

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Numeric Types 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by