I was wondering how it is possible to save an image created by imshow in matlab. The code below uses the imshow function with the min and max arguments specified - How can I apply this directly to the image itself instead of just specifying Matlab to show it?
maxBlur=3;
a = imshow(fDmap,[0 maxBlur]);
imwrite(a, 'img.png');
Writing to the file produces a different output to what is shown via imshow.
Can anyone suggest how to get the output from imshow saved as an image?
To specify upper and lower intensity limits for imwrite (similar to what you've done for imshow), you will want to use the second inputs to mat2gray to adjust the contrast of your image prior to saving it with imwrite.
imwrite(mat2gray(fDmap, [0 maxBlur]), 'img.png');
If you literally want an image of what you're seeing with imshow, you can use saveas to take a screenshot. This will potentially be lower resolution than the previous approach and will also include whitespace around the image.
imshow(fDmap, [0 maxBlur]);
saveas(gcf, 'img.png');
NOTE: The a variable that you passed to imwrite in your post is a MATLAB graphics handle to an image object that is used to manipulate the rendered image. imwrite expects image data in matrix form not as a graphics handle.
Related
I have a medical imaging matrix of size [200x200x200].
In order to display it, I am currently using imshow3D function, which is an excellent tool, built by Maysam Shahedi.
This tool displays the 3D image slice by slice, with mouse based slice browsing
In my current project, I generate an RGB image for each z-layer from the original input image. The output is a 3D color image of size [200x200x200x3] (each layer is now represented by 3 channels).
The imshow3D function works great on grayscale images. Is it possible to use it to display RGB images?
I took a look at this nice imshow3D function from Matlab FileExchange, and it is quite straight-forward to change it to allow working with a stack of RGB images.
The magic part of the function is
imshow(Img(:,:,S))
which displays the slice S of the image Img. We can simply change it to show all 3 channels of image S by changing this to Img(:,:,S,:). The result will be of size 200-by-200-by-1-by-3, while MATLAB expects RGB images to be of size 200-by-200-by-3. Simply squeeze this image to get the correct dimension. This results in:
imshow(squeeze(Img(:,:,S,:))
So to show RGB images, do a search-and-replace inside the function imshow3D, to replace all occurrences of Img(:,:,S) with squeeze(Img(:,:,S,:)) and it works!
I am using HDF satellite data to retrieve bands from that I am concluding different vegetation indices. Every band in hdf data is in grey colour format, its a grey colour scale image. After HDF data processed I can convert into colour by using colour map (I am using jet for colourmap). My doubt is how to convert greyscale image into colourmaped while using imwrite. How to use colourmap within imwrite. I have tried many times, but the output is only in full blue colour, this spoil the output image. Please help me to do this.
Why use imwrite? You can use imshow.
Example:
imshow(im)
imshow(im,'Colormap',jet(255))
With reference: http://www.alecjacobson.com/weblog/?p=1655
Try using the ind2rgb function before using imwrite if you want to save to a format like .jpg, but if you are using an indexing image format (e.g. .png) you can just use imwrite directly as shown in the docs:
imwrite(X, map, filename)
where X is your greyscale image, map is your colourmap (i.e. jet) and filename is the is the name of the image you want to save ending in .png
I am currently using getframe() and frame2im in MATLAB to convert a figure of a plot to an image.
I just realized that this is working almost like a screenshot of the figure, with all the axes and labels taken into account as well.
How can I convert JUST the contents of the figure (aka the "plot") into an image?
I don't really want to save all of them to file first.
You can use the getframe / cdata idiom. What this will do is that if you call getframe on the current frame in focus without any parameters, it will return a structure to you that contains a structure element called cdata. This stores the RGB pixel array of just the figure contents themselves. The axes and labels are not captured - only what is painted onto the figure is captured.
Here's an example to get you started:
im = imread('cameraman.tif');
imshow(im);
h = getframe;
out = h.cdata;
figure;
imshow(out); %// Should give you the contents within the imshow frame.
FWIW, I also answered this same question here, though it was for a different situation: keep new image when drawing lines by dragging the mouse in matlab
As far as i know, cdata DOES NOT WORK. I had a major problem recently with the same thing - the only work around i could find is to crop each image after using getframe and cdata - this will work fine for images that are all the same size (ugly as it is - you just need to find the grey edges in the image), but if the images are all different, this wont work (well, it wont work well. there might be some way to automatically adjust the crop size)
I'm analyzing some sound clips using the spectrogram() function in MATLAB. I would like to save the spectrogram as an image (jpg, png, etc). But regardless of what image format I save the figure in, the resulting image always looks different ("spotty") from what I see in the figure.
Here's an example of the spectrograms: Matlab Figure vs. Saved Image
All I want is to save exactly what I see in the figure as an image. I've already tried saving the figure in all the image formats possible but all of them are producing the same "spotting" effect. I've also tried both manual saving (click on file -> save as) and programmatically using the print() and the saveas() functions. Same result every time.
Any help would be appreciated!
What is the data range of your spectrogram?
One of reasons might be that your spectrogram range is out of the [0,1] region for double images or [0,255] for uint* images (your white spots on saved image are suspiciously close to the local minima on MatLab figure).
Another guess might be that you are using imwrite function, in particular its imwrite(X,map,filename,fmt) syntax. MatLab documentation explains:
imwrite(X,map,filename,fmt) writes the indexed image in X and its associated colormap map to filename in the format specified by fmt. If X is of class uint8 or uint16, imwrite writes the actual values in the array to the file. If X is of class double, imwrite offsets the values in the array before writing, using uint8(X–1). map must be a valid MATLAB colormap. Note that most image file formats do not support colormaps with more than 256 entries.
so the uint8(X–1) might be the source of the white spots.
Though have no idea why they appear after print()'ing.
I found a work-around for this problem by using the pcolor() function, which is essentially a rotated surf() function plotted in a grid format (doc). After tinkering with the spectrogram() function more, I'm convinced that these "spotting" artifacts have nothing to do with the data format, property, or scale. The problem seems to lie in the way MATLAB plots and visualizes 3D plots. I tried plotting with the mesh() function as well and it produced a different kind of "spotting" effect. pcolor() works because it's a 2D visualization of a 3D plot.
This is how spectrogram() plots the image using surf() (adapted from the doc):
[S,T,F,P] = spectrogram(X,256,250,256,2000);
surf(T,F,abs(S),'EdgeColor','none');
axis tight; view(0,90);
... and this is how to use pcolor() to plot a save-friendly image:
[S,T,F,P] = spectrogram(X,256,250,256,2000);
h = pcolor(T,F,abs(S));
set(h,'EdgeColor','none');
The white spots are an OpenGL issue, which is the renderer used in spectrogram()'s internal call to surf().
Since you are interested in plotting a 2D visualization, change the renderer for the current figure to zbuffer:
set(gcf, 'renderer', 'zbuffer');
where gcf means "get current figure". The white spots are now gone.
Note that you can also select the zbuffer renderer when you create the figure, before calling spectrogram():
myNewFig = figure('renderer','zbuffer');
I was wondering how it is possible to save an image created by imshow() in matlab. The code below uses the imshow() function with the min and max arguments specified - How can I apply this directly to the image itself instead of just specifying Matlab to show it?
imshow(img4fft, [1 300000]);
imwrite(img4fft, 'img.png');
Writing to the file produces a different output to what is shown via imshow().
Can anyone suggest how to get the output from imshow() saved as an image?
Many thanks MatLab is an alien language to me!
I obtain the same result by doing:
img4fft2=min(double(img4fft),300000)/300000;
imwrite(img4fft2,'img.png');
You could apply saturation to the image manually:
I2 = imadjust(I, [0,30000],[0,2^{resolution}-1]);
imwrite('out.png', I2);