Problem with Imhist method

Question

Jason 2014-10-23

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评论： Jason 2014-10-23

I have an image Zoom:

Zoom =

  313    269    237    255    329
  271    304    256    332    302
  320    265    215    274    316
  219    218    224    221    224
  224    203    226    193    210
  231    219    227    205    227

when I perform

figure
imhist(Zoom)

the histogram is defaulting in the x-axis to x10^4

So the histogram is just a spike.

why does it not autorange the x-axis, and how too?

thanks Jason

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Jason 2014-10-23

Just to add, I often use 12 bit images. Occasionally I will use the sum of 3, 12 bit images, so I need the capability to handle both. I would like to limit the number of bins to say 100, but have the x-axis represent the actual intensity, with the max of the x-axis being soemthing related to the max value of intensity in data set

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Answer 1

Image Analyst 2014-10-23

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编辑：Image Analyst 2014-10-23

在 MATLAB Online 中打开

It's using the max of the data type, which is uint16. You can set the x axis to the max of the image varaible after you call imhist() like this:

xlim([0, max(Zoom(:)));

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Answer 2

Michael Haderlein 2014-10-23

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在 MATLAB Online 中打开

The x scale depends on the data type of the image. I guess in your case, Zoom is of uint16? Then, the limits of the data are [0 65535] and that's the limits of the axes.

Now, the question is, how do to better in your case. Converting to the next smaller data type (uint8) won't help a lot as you have numbers too big for uint8 (must be max 255). Depending on your specific problem, I'd

- either normalize to max=1:

imhist(Zoom/max(Zoom(:)))

- or use the "normal" hist function:

hist(Zoom(:),1:max(Zoom(:)))

Best regards,

Michael

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Jason 2014-10-23

在 MATLAB Online 中打开

OK, Im playing with the following, but its not quite there:

%Automate x-axis labels---------------------------------------
[maxval1,idx]=double(max(ROI(:)))
XTck=get(handles.axes6,'XTick');
t_lim = 1e3*ceil(maxval/1000)       % get axis limit: 5000
t_ax  = 0:t_lim;
n_int = 20;                          % define # of intervals
t_int = t_lim/n_int;
tt    = t_ax(rem(t_ax,t_int)==0);   % find tick locations
ttlab = num2cell(tt)               % and generate tick labels
%---------------------------------------------------------------
[counts,x] = imhist(ROI,n_int);
set(handles.axes6,'XTick', tt,'XTickLabel',ttlab);
xlim([0 maxval])

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Answer 3

Adam 2014-10-23

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I'm not familiar with imhist, but from a quick look it appears to always use the data type limits for its histogram range so I guess you would need to scale your data up to make better use of the available data range for a histogram using imhist.