How to save the image WITHOUT the white background using imwrite (advanced problem)

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Salad Box
Salad Box 2019-9-3
编辑： Salad Box 2019-9-3
Hi
RGB = imread('bird1.png');
figure
imshow(RGB)
Then I get:
Then:
s = size(RGB);
rectangle('position',[1 1 s(2) s(1)], 'edgecolor', [1 0 0])
rectangle('position',[0 0 s(2) s(1)], 'edgecolor', [1 0 0])
I get:
Now I would like to save this image WITHOUT the white background, only the content within the red box (including the red box).
Imwrite needs to use 'RGB', however after the red box been added onto the image, RGB is no longer the original RGB. It WON'T be correct just to use
imwrite(RGB, 'bird1.png');
Could anyone provide correct solution to this question please?
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Salad Box
Salad Box 2019-9-3
Hi Adam,
The reason that I need to remove the border/background of the image is I have to put the image on to my own background (dark-grey or black). See example below.
bird4.png
One more requirement is that I have to add box around the image (in this case it is red box). It would look extremely odd/ inappropriate to present a white border between the red box and the black background as the left one in the above image.
Above bird image is just an example image.
In reality all my images are small.
iptsetpref('ImshowBorder','tight');
would work on large images but won't work on small images as stated in the official documents.
bird5.png
Please help.
Adam
Adam 2019-9-3
Ah well, that is different! None of the images you previously showed had any white background outside the red rectangle so I assumed you meant the white within it.

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采纳的回答

Image Analyst
Image Analyst 2019-9-3
Try this:
% To burn the color into the image itself.
[rows, columns, numberOfCOlorChannels] = size(RGB)
RGB(:, 1, 1:3) = repmat([255, 0, 0], rows, 1);
RGB(:, end, 1:3) = repmat([255, 0, 0], rows, 1);
RGB(1, :, 1:3) = repmat([255, 0, 0], columns, 1);
RGB(end, :, 1:3) = repmat([255, 0, 0], columns, 1);
imshow(RGB);
imwrite(RGB, filename);
It's much more robust than saving the bitmap in the overlay, which is subject to change whenever you resize the figure window.

更多回答（1 个）

Johannes Fischer
Johannes Fischer 2019-9-3
% read image as NxMx3 rgb matrix
RGB = imread('bird1.png');
imshow(RGB)
s = size(RGB);
rectangle('position',[1 1 s(2) s(1)], 'edgecolor', [1 0 0])
rectangle('position',[0 0 s(2) s(1)], 'edgecolor', [1 0 0])
% get a handle of the axis
F = getframe(gca);
% and save the color information of the axis, which is stored as RGB in
% the field 'cdata'
imwrite(F.cdata, 'bird2.png')
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Salad Box
Salad Box 2019-9-3
Actually as I used Johannes Fischer's method on batch size (approximate 300 images), my Matlab crashed.
I restarted my PC and Matlab, I got this message:
"Warning: MATLAB previously crashed due to a low-level graphics error. To
prevent another crash in this session, MATLAB is using software OpenGL instead
of using your graphics hardware. To save this setting for future sessions, use
the opengl('save', 'software') command. For more information, see Resolving
Low-Level Graphics Issues. "
>>
I hope this has got nothing to do with your method Johannes Fischer.
Johannes Fischer
Johannes Fischer 2019-9-3
Interesting... it seems to be larger by one pixel in row or column dimension, depending on the input size. I thought it would keep the size as long as no resizing is performed.
But you're right, you're solution is more robust, and in terms of batch processing probably much faster.

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