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  • How to add legend to imshow() in matplotlib

    - by rankthefirst
    I am using matplotlib In plot() or bar(), we can easily put legend, if we add labels to them. but what if it is a contourf() or imshow() I know there is a colorbar() which can present the color range, but it is not satisfied. I want such a legend which have names(labels). For what I can think of is that, add labels to each element in the matrix, then ,try legend(), to see if it works, but how to add label to the element, like a value?? in my case, the raw data is like: 1,2,3,3,4 2,3,4,4,5 1,1,1,2,2 for example, 1 represents 'grass', 2 represents 'sand', 3 represents 'hill'... and so on. imshow() works perfectly with my case, but without the legend. my question is: Is there a function that can automatically add legend, for example, in my case, I just have to do like this: someFunction('grass','sand',...) If there isn't, how do I add labels to each value in the matrix. For example, label all the 1 in the matrix 'grass', labell all the 2 in the matrix 'sand'...and so on. Thank you!

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  • OpenCV 2.0 C++ API using imshow: returns unhandled exception and "bad-flag"

    - by Konrad
    I'm trying to use the new OpenCV 2.0 API in MS Visual C++ 2008 and wrote this simple program: cv::Mat img1 = cv::imread("image.jpg",1); cv::namedWindow("My Window", CV_WINDOW_AUTOSIZE); cv::imshow("My Window", img1); Visual Studio returnes an unhandled exception and the Console returns: OpenCV Error: bad flag (parameter or structure field) (Unrecognized or unsupported array type) in unknown function, file ..\..\..\..\ocv\opencv\src\cxcore\cxarray.cpp, line 2376 The image is not displayed. Furthermore the window "My Window" has a strange caption: "ÌÌÌÌMy Window", which is not dependent on the name. The "old" C API using commands like cvLoadImage, cvNamedWindow or cvShowImage works without any problem for the same image file. I tried a lot of different stuff without success. I appreciate any help here. Konrad

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  • How can I plot NaN values as a special color with imshow in matplotlib?

    - by Adam Fraser
    example: import numpy as np import matplotlib.pyplot as plt f = plt.figure() ax = f.add_subplot(111) a = np.arange(25).reshape((5,5)).astype(float) a[3,:] = np.nan ax.imshow(a, interpolation='nearest') f.canvas.draw() The resultant image is unexpectedly all blue (the lowest color in the jet colormap). However, if I do the plotting like this: ax.imshow(a, interpolation='nearest', vmin=0, vmax=24) --then I get something better, but the NaN values are drawn the same color as vmin... Is there a graceful way that I can set NaNs to be drawn with a special color (eg: gray or transparent)?

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  • How can I link axes of imshow plots for zooming and panning?

    - by Adam Fraser
    Suppose I have a figure canvas with 3 plots... 2 are images of the same dimensions plotted with imshow, and the other is some other kind of subplot. I'd like to be able to link the x and y axes of the imshow plots so that when I zoom in one (using the zoom tool provided by the NavigationToolbar), the other zooms to the same coordinates, and when I pan in one, the other pans as well. Subplot methods such as scatter and histogram can be passed kwargs specifying an axes for sharex and sharey, but imshow has no such configuration. I started hacking my way around this by subclassing NavigationToolbar2WxAgg (shown below)... but there are several problems here. 1) This will link the axes of all plots in a canvas since all I've done is get rid of the checks for a.in_axes() 2) This worked well for panning, but zooming caused all subplots to zoom from the same global point, rather than from the same point in each of their respective axes. Can anyone suggest a workaround? Much thanks! -Adam from matplotlib.backends.backend_wxagg import NavigationToolbar2WxAgg class MyNavToolbar(NavigationToolbar2WxAgg): def __init__(self, canvas, cpfig): NavigationToolbar2WxAgg.__init__(self, canvas) # overrided # As mentioned in the code below, the only difference here from overridden # method is that this one doesn't check a.in_axes(event) when deciding which # axes to start the pan in... def press_pan(self, event): 'the press mouse button in pan/zoom mode callback' if event.button == 1: self._button_pressed=1 elif event.button == 3: self._button_pressed=3 else: self._button_pressed=None return x, y = event.x, event.y # push the current view to define home if stack is empty if self._views.empty(): self.push_current() self._xypress=[] for i, a in enumerate(self.canvas.figure.get_axes()): # only difference from overridden method is that this one doesn't # check a.in_axes(event) if x is not None and y is not None and a.get_navigate(): a.start_pan(x, y, event.button) self._xypress.append((a, i)) self.canvas.mpl_disconnect(self._idDrag) self._idDrag=self.canvas.mpl_connect('motion_notify_event', self.drag_pan) # overrided def press_zoom(self, event): 'the press mouse button in zoom to rect mode callback' if event.button == 1: self._button_pressed=1 elif event.button == 3: self._button_pressed=3 else: self._button_pressed=None return x, y = event.x, event.y # push the current view to define home if stack is empty if self._views.empty(): self.push_current() self._xypress=[] for i, a in enumerate(self.canvas.figure.get_axes()): # only difference from overridden method is that this one doesn't # check a.in_axes(event) if x is not None and y is not None and a.get_navigate() and a.can_zoom(): self._xypress.append(( x, y, a, i, a.viewLim.frozen(), a.transData.frozen())) self.press(event)

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  • How can I draw a log-normalized imshow plot with a colorbar representing the raw data in matplotlib

    - by Adam Fraser
    I'm using matplotlib to plot log-normalized images but I would like the original raw image data to be represented in the colorbar rather than the [0-1] interval. I get the feeling there's a more matplotlib'y way of doing this by using some sort of normalization object and not transforming the data beforehand... in any case, there could be negative values in the raw image. import matplotlib.pyplot as plt import numpy as np def log_transform(im): '''returns log(image) scaled to the interval [0,1]''' try: (min, max) = (im[im > 0].min(), im.max()) if (max > min) and (max > 0): return (np.log(im.clip(min, max)) - np.log(min)) / (np.log(max) - np.log(min)) except: pass return im a = np.ones((100,100)) for i in range(100): a[i] = i f = plt.figure() ax = f.add_subplot(111) res = ax.imshow(log_transform(a)) # the colorbar drawn shows [0-1], but I want to see [0-99] cb = f.colorbar(res) I've tried using cb.set_array, but that didn't appear to do anything, and cb.set_clim, but that rescales the colors completely. Thanks in advance for any help :)

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  • Function template overloading: link error

    - by matt
    I'm trying to overload a "display" method as follows: template <typename T> void imShow(T* img, int ImgW, int ImgH); template <typename T1, typename T2> void imShow(T1* img1, T2* img2, int ImgW, int ImgH); I am then calling the template with unsigned char* im1 and char* im2: imShow(im1, im2, ImgW, ImgH); This compiles fine, but i get a link error "unresolved external symbol" for: imShow<unsigned char,char>(unsigned char *,char *,int,int) I don't understand what I did wrong!

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  • How do I set a matplotlib colorbar extents?

    - by Adam Fraser
    I'd like to display a colorbar representing an image's raw values along side a matplotlib imshow subplot which displays that image, normalized. I've been able to draw the image and a colorbar successfully like this, but the colorbar min and max values represent the normalized (0,1) image instead of the raw (0,99) image. f = plt.figure() # create toy image im = np.ones((100,100)) for x in range(100): im[x] = x # create imshow subplot ax = f.add_subplot(111) result = ax.imshow(im / im.max()) # Create the colorbar axc, kw = matplotlib.colorbar.make_axes(ax) cb = matplotlib.colorbar.Colorbar(axc, result) # Set the colorbar result.colorbar = cb If someone has a better mastery of the colorbar API, I'd love to hear from you. Thanks! Adam

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  • Variable alpha blending in pylab

    - by Hooked
    How does one control the transparency over a 2D image in pylab? I'd like to give two sets of values (X,Y,Z,T) where X,Y are arrays of positions, Z is the color value, and T is the transparency to a function like imshow but it seems that the function only takes alpha as a scalar. As a concrete example, consider the code below that attempts to display two Gaussians. The closer the value is to zero, the more transparent I'd like the plot to be. from pylab import * side = linspace(-1,1,100) X,Y = meshgrid(side,side) extent = (-1,1,-1,1) Z1 = exp(-((X+.5)**2+Y**2)) Z2 = exp(-((X-.5)**2+(Y+.2)**2)) imshow(Z1, cmap=cm.hsv, alpha=.6, extent=extent) imshow(Z2, cmap=cm.hsv, alpha=.6, extent=extent) show() Note: I am not looking for a plot of Z1+Z2 (that would be trivial) but for a general way to specify the alpha blending across an image.

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  • Creating a Colormap Legend in Matplotlib

    - by Vince
    Hi fellow Stackers! I am using imshow() in matplotlib like so: import numpy as np import matplotlib.pyplot as plt mat = '''SOME MATRIX''' plt.imshow(mat, origin="lower", cmap='gray', interpolation='nearest') plt.show() How do I add a legend showing the numeric value for the different shades of gray. Sadly, my googling has not uncovered an answer :( Thank you in advance for the help. Vince

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  • showing .tif images in matlab

    - by sepideh
    I am trying to show a .tif image in matlab and I use these two line of codes a = imread('C:\Users\sepideh\Desktop\21_15.tif'); imshow(a) that encounters this warning Warning: Image is too big to fit on screen; displaying at 3% In imuitools\private\initSize at 73 In imshow at 262 what is the cause of this warning and what can I do to fix that? the main trouble is it sometimes doesn't show the image and of course even if it shows the image CPU usage gets high that I can't zoom properly

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  • BMP2AVI program in matlab

    - by ariel
    HI I wrote a program that use to work (swear to god) and has stopped from working. this code takes a series of BMPs and convert them into avi file. this is the code: path4avi='C:/FadeOutMask/'; %dont forget the '/' in the end of the path pathOfFrames='C:/FadeOutMask/'; NumberOfFiles=1; NumberOfFrames=10; %1:1:(NumberOfFiles) for i=0:1:(NumberOfFiles-1) FileName=strcat(path4avi,'FadeMaskAsael',int2str(i),'.avi') %the generated file aviobj = avifile(FileName,'compression','None'); aviobj.fps=10; for j=0:1:(NumberOfFrames-1) Frame=strcat(pathOfFrames,'MaskFade',int2str(i*10+j),'.bmp') %not a good name for thedirectory [Fa,map]=imread(Frame); imshow(Fa,map); F=getframe(); aviobj=addframe(aviobj,F) end aviobj=close(aviobj); end And this is the error I get: ??? Error using ==> checkDisplayRange at 22 HIGH must be greater than LOW. Error in ==> imageDisplayValidateParams at 57 common_args.DisplayRange = checkDisplayRange(common_args.DisplayRange,mfilename); Error in ==> imageDisplayParseInputs at 79 common_args = imageDisplayValidateParams(common_args); Error in ==> imshow at 199 [common_args,specific_args] = ... Error in ==> ConverterDosenWorkd at 19 imshow(Fa,map); for some reason I cant put it as code segments. sorry thank you Ariel

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  • How to map coordinates in AxesImage to coordinates in saved image file?

    - by Vebjorn Ljosa
    I use matplotlib to display a matrix of numbers as an image, attach labels along the axes, and save the plot to a PNG file. For the purpose of creating an HTML image map, I need to know the pixel coordinates in the PNG file for a region in the image being displayed by imshow. I have found an example of how to do this with a regular plot, but when I try to do the same with imshow, the mapping is not correct. Here is my code, which saves an image and attempts to print the pixel coordinates of the center of each square on the diagonal: import numpy as np import matplotlib.pyplot as plt fig = plt.figure() ax = fig.add_axes([0.1, 0.1, 0.8, 0.8]) axim = ax.imshow(np.random.random((27,27)), interpolation='nearest') for x, y in axim.get_transform().transform(zip(range(28), range(28))): print int(x), int(fig.get_figheight() * fig.get_dpi() - y) plt.savefig('foo.png', dpi=fig.get_dpi()) Here is the resulting foo.png, shown as a screenshot in order to include the rulers: The output of the script starts and ends as follows: 73 55 92 69 111 83 130 97 149 112 … 509 382 528 396 547 410 566 424 585 439 As you see, the y-coordinates are correct, but the x-coordinates are stretched: they range from 73 to 585 instead of the expected 135 to 506, and they are spaced 19 pixels o.c. instead of the expected 14. What am I doing wrong?

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  • Problem with xor operation

    - by gavishna
    Kindly tell me why the original image is not coming with this code. The resulting image receive is yellowish in color,instead of being similar to the image Img_new Img=imread(‘lena_color.tif’); Img_new=rgb2gray(img); Send=zeroes(size(Img_new); Receive= zeroes(size(Img_new); Mask= rand(size(Img_new); for i=1 :256 for j=1:256 Send(i,j)=xor( Img_new(i,j),mask(i,j)); End End image(send); imshow(send); for i=1 :256 for j=1:256 receive(i,j)=xor( send(i,j),mask(i,j)); End End image(receive); imshow(receive); plz help

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  • function taking in an input image and different kernel size

    - by drifterOcean19
    I have this filtering function that takes an input image, performs convolution using a given kernel, and returns the resulting image. However, I can't seem to work it out how to make it takes different kernel sizes.For example instead of pre-defined 3x3 kernel as below in the code, it could instead take 5x5 or 7x7. and then the user could input the type of kernel/filter they want(Depending on the intended effect). I can't seem to put my head around it. i'm quite new to matlab. function [newImg] = kernelFunc(imgB) img=imread(imgB); figure,imshow(img); img2=zeros(size(img)+2); newImg=zeros(size(img)); for rgb=1:3 for x=1:size(img,1) for y=1:size(img,2) img2(x+1,y+1,rgb)=img(x,y,rgb); end end end for rgb=1:3 for i= 1:size(img2,1)-2 for j=1:size(img2,2)-2 window=zeros(9,1); inc=1; for x=1:3 for y=1:3 window(inc)=img2(i+x-1,j+y-1,rgb); inc=inc+1; end end kernel=[1;2;1;2;4;2;1;2;1]/16; med=window.*kernel; disp(med); med=sum(med); med=floor(med); newImg(i,j,rgb)=med; end end end newImg=uint8(newImg); figure,imshow(newImg); end

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  • Grayscale in matlab

    - by ruthenium
    I'm trying to convert a 2D array to grayscale but using mat2gray doesn't do anything and imshow() appears to create a binary image that when I graph I cannot rotate it, e.g. the original array is 2d but maps in 3d. So, what is the best way to take a grayscale of 2d array in Matlab so if you have A=rand(5,10) or something and want to take a grayscale of that, what is the best way?

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  • What is the fastest way to scale and display an image in Python?

    - by Knut Eldhuset
    I am required to display a two dimensional numpy.array of int16 at 20fps or so. Using Matplotlib's imshow chokes on anything above 10fps. There obviously are some issues with scaling and interpolation. I should add that the dimensions of the array are not known, but will probably be around thirty by four hundred. These are data from a sensor that are supposed to have a real-time display, so the data has to be re-sampled on the fly.

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  • Need a explanation for the matlab code snippet

    - by Mask
    %# load a grayscale image img = imread('coins.png'); %# display the image figure imshow(img,[]); %# false-color colormap('hot') The above code is from here: http://stackoverflow.com/questions/2592755/infrared-image-processing-in-matlab/2592793#2592793 But I don't understand how figure(What's the difference with/without it?) and colormap(How does it affect the already shown img?) work?

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  • How to unblend two images from a blend image

    - by gavishna
    I have blended/merged 2 images img1 and img2 with this code which is woking fine.What i want to know is how to obtain the original two images img1 and img2.The code for blending is as under img1=imread('C:\MATLAB7\Picture5.jpg'); img2=imread('C:\MATLAB7\Picture6.jpg'); for i=1:size(img1,1) for j=1:size(img1,2) for k=1:size(img1,3) output(i,j,k)=(img1(i,j,k)+img2(i,j,k))/2; end end end imshow(output,[0 255]);

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  • Is it possible to see the underlying implementation of built in functions of matlab?

    - by user198729
    I'm using this example code to grayscale an image,but the result is not right: I = imread('coins.png'); level = graythresh(I); BW = im2bw(I,level); imshow(BW) Where to see how graythresh is actually implemented? BTW,is there a reason for using matlab feels so alike with python? Or is it known that graythresh doesn't work well for images with little spatial resolution(like 62*21 ones)?

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  • matplotlib equivalent for MATLABs truesize()

    - by Lucas
    I am new to matplotlib and python and would like to display an image so that 1 pixel of the image is actually represented by 1 pixel in the figure. In MATLAB, this is achieved with the command truesize(). How can I do this in Python? I tried playing around with the imshow() arguments as well as set_dpi() and set_figwidth()/set_figheight(), but with no luck. Thanks.

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  • AttributeError while adding colorbar in matplotlib

    - by bgbg
    The following code fails to run on Python 2.5.4: from matplotlib import pylab as pl import numpy as np data = np.random.rand(6,6) fig = pl.figure(1) fig.clf() ax = fig.add_subplot(1,1,1) ax.imshow(data, interpolation='nearest', vmin=0.5, vmax=0.99) pl.colorbar() pl.show() The error message is C:\temp>python z.py Traceback (most recent call last): File "z.py", line 10, in <module> pl.colorbar() File "C:\Python25\lib\site-packages\matplotlib\pyplot.py", line 1369, in colorbar ret = gcf().colorbar(mappable, cax = cax, ax=ax, **kw) File "C:\Python25\lib\site-packages\matplotlib\figure.py", line 1046, in colorbar cb = cbar.Colorbar(cax, mappable, **kw) File "C:\Python25\lib\site-packages\matplotlib\colorbar.py", line 622, in __init__ mappable.autoscale_None() # Ensure mappable.norm.vmin, vmax AttributeError: 'NoneType' object has no attribute 'autoscale_None' How can I add colorbar to this code? Following is the interpreter information: Python 2.5.4 (r254:67916, Dec 23 2008, 15:10:54) [MSC v.1310 32 bit (Intel)] on win32 Type "help", "copyright", "credits" or "license" for more information. >>>

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