Why is an image of class type double seen completely white when the function imshow is used in matlab?This seems to be the case with every image
By default, imshow expects images of type double to be in the range [0,1].
As a solution, you can do the following:
imshow(img, [])
This is equivalent to:
imshow(img, 'DisplayRange',[min(img(:)) max(img(:))])
Alternatively you can manually normalize the image to the expected [0,1] range.
You can use im2double:
imshow(im2double(I))
Related
I have a problem with imcontrast tool.
I read 2D dicom image, then convert it to 16bits(im2uint16) and perform filtration and windowing using imcontrast.
It shows me a warning message:
How Can I prevent then ?
How can I change data range in imtool ?
I would appreciate for any help please.
The [0,51156] is the range of the image data which change from image to image. [0, 65535] are the default color axis limits for uint16, which are outside the image data range, causing the re-adjust warning prompt. If you wish to silence the prompt you can manually set the color axis limits before calling imcontrast by:
caxis([double(min(min(Image))), double(max(max(Image)))]);
The conversion to double is to prevent a datatype mismatch. max() and min() return an uint16 value with uint16 data, which causes an another error down the line.
I am preparing some figures for a paper printed in black and white. I thought that easiest way to do so was to change the default colormap to gray. However I'm stuck with the following error:
set(0,'DefaultFigureColormap',gray);
Error using set
Value must be either:
an Mx3 array of type single or double in the range [0 1]
an Mx3 array of type uint8
You can use the built-in function rgb2gray to convert from RGB. There are other such alternatives mentioned in the Image Processing Toolbox.
I'm using the Images package and I want to load in an image and get the mean and standard deviation of the pixels in r image.
I tried:
using Images, Color, FixedPointNumbers, ImageView, Testimages
img = testimage("mandril")
mean(data(img))
The mean worked fine, in fact in IJulia it displays the mean color of the image. However, when I tried to get the standard deviation of the image, I get:
std(data(img))
`varm` has no method matching varm(::Image{RGB{UfixedBase{Uint8,8}},2,Array{RGB{UfixedBase{Uint8,8}},2}}, ::RGB{Float32})
while loading In[66], in expression starting on line 1
in var at statistics.jl:162
How would one go about getting the standard deviation of the image?
You can use red, green and blue to extract the components of image,
and compute the standard deviation with std on the resulting matrices.
using Images
using TestImages
using Color
img = testimage("mandril")
data(img)
RGB(
std(red(img)),
std(green(img)),
std(blue(img))
)
# RGB{Float32}(0.22030124f0,0.18964756f0,0.24422659f0)
You could also build a 3-dimensional array with all the data,
with separate,
and apply std on the three 2-dimensional slices corresponding
to the three components, with mapslices.
vec( mapslices( std, separate(img), [1,2] ) )
If you want to figure out why mean(data(img)) works
and std(data(img)) does not (at least, currently),
you can check which method is called
with #which, and read the corresponding code, with #less.
#which mean(data(img))
# mean(A::AbstractArray{T,N}) at statistics.jl:17
#which std(data(img))
# std(A::AbstractArray{T,N}) at statistics.jl:204
#less mean(data(img))
#less std(data(img))
There are (at least) two problems: first, sqrt is not defined for colours,
second, some of the code in std assumes that the mean is a Number.
I found that apparently, a mapped version of imshow function does not work in subplot. Is this by design?
The following script
rgb=imread('../FruitSample_small.png');
[ind,map]=rgb2ind(rgb,4);
figure
imshow(ind,map)
figure
subplot(5,1,1);
imshow(ind,map)
subplot(5,1,2);
imshow(ind==0)
subplot(5,1,3);
imshow(ind==1)
subplot(5,1,4);
imshow(ind==2)
subplot(5,1,5);
imshow(ind==3)
produces the following result
i.e. mapped version looks black. If I plot mapped version only (5 times) it looks ok. I.e. subsequent plotting apparently change the palette.
How to plot all these 5 images on same figure then?
Colormap is a property of the figure, not the axis. The second call to imshow resets the Colormap for the entire figure. Here is some more information and a Matlab file exchange solution to the problem. If you download the function described in that link, freezeColors, you can use it in your code like this.
rgb=imread('peppers.png'); % example image included in matlab
[ind,map]=rgb2ind(rgb,4);
figure
imshow(ind,map)
figure
subplot(5,1,1);
imshow(ind,map)
freezeColors % keep colors the same after other subplots are displayed
subplot(5,1,2);
imshow(ind==0)
freezeColors
subplot(5,1,3);
imshow(ind==1)
subplot(5,1,4);
imshow(ind==2)
subplot(5,1,5);
imshow(ind==3)
And the resulting second figure will look like this:
I have a double 2D image that I want to use in my UI that I made with guide. I have a axis handle which I want to draw it to. I tried this with no success, my image is all blue.
function ComputeMap_Callback(hObject, eventdata, handles)
% hObject handle to ComputeMap (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
global healthyImage;
global sickImage;
global tumorMapImage;
global costFunction;
if(get(handles.radiobuttonMSE,'Value') == get(hObject,'Max'))
costFunction = 0;
else
costFunction = 1;
end
disp(costFunction);
tumorMapImage = mexFunction(im2double(sickImage),im2double(healthyImage),get(handles.blockSize,'Value'),get(handles.windowSize,'value'), costFunction);
image(tumorMapImage,'parent',handles.sImageGUI);
This mexFunction returns a double 2D image. If I just call this function without matlab and imShow (resultImage); I get the right result. So I believe it has something to do with the colormapping of the double and the fact that the image is not 3D but 2D. But I am 0 familiar with gui in matlab to be sure what to do. I've done some more researches and I think my problem might be related to the AlphaData property, but I don't know what to do with that.
your image values must be in range [0, 1] in order to be plotted properly by the image function.
imshow works because it first looks at the min and max value in your image and then scales values to match this range. or so. (maybe it works differently internally, but whatever..)