Databases
StackOverflow2013
Postsdbo
POFastest way to crop an image without exceeding image dimensions in Matlab
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POFastest way to crop an image without exceeding image dimensions in Matlab
    primarykey
    data
    text
    <p>Using matlab.</p> <p>Suppose I have:</p> <ul> <li>An image <code>i</code> with "MaxWidth" number of pixels in the horizontal direction and "MaxHeight" number of pixels in the vertical direction. </li> <li>A retangular ROI defined by the coordinates of the top-left and bottom-right pixels as in </li> </ul> <p><code>ROI = [yleft , xleft ; yright , xright]</code></p> <p>I was wondering what would be the fastest way to compute <code>i_crop</code>, where <code>i_crop</code>is the image that contains only the pixels that were in <code>i</code> and inside the given ROI. </p> <p>ROI's like <code>[-10 , -10 ; 1000 , 1000]</code> in an 400x400 image should be regarded as <code>[1 , 1 ; 400 , 400]</code></p> <hr> <p>I came up with both of this so far:</p> <h2>crop1</h2> <pre><code>ROI(ROI&lt;1)=1; ROI(ROI(:,1)&gt;MaxHeight) = MaxHeight; ROI(find(ROI(:,2)&gt;MaxWidth)+2) = MaxWidth; i_crop = i(ROI(1,1):ROI(2,1),ROI(1,2):ROI(2,2),:); </code></pre> <p>And</p> <h2>crop2</h2> <pre><code>ymin = ROI(1,1); xmin = ROI(1,2); ymax = ROI(2,1); xmax = ROI(2,2); if ymin &lt; 1 ymin = 1; end if xmin &lt; 1 xmin = 1; end if ymax &lt; 1 ymax = 1; end if xmax &lt; 1 xmax = 1; end if ymin &gt; MaxHeight ymin = MaxHeight; end if ymax &gt; MaxHeight ymax = MaxHeight; end if xmin &gt; MaxWidth xmin = MaxWidth; end if xmax &gt; MaxWidth xmax = MaxWidth; end i_crop = i(ymin:ymax,xmin:xmax,:); </code></pre> <p>The latter runs faster:</p> <pre><code>&gt;&gt; im = imread('peppers.png'); &gt;&gt; tic, for i =1:100000 i_c = crop1(im,[0 0 ; 60 60],512,384); end; toc; Elapsed time is 2.053574 seconds. &gt;&gt; tic, for i =1:100000 i_c = crop2(im,[0 0 ; 60 60],512,384); end; toc; Elapsed time is 1.667059 seconds. </code></pre> <p>Hope I made myself clear, thank's in advance!</p>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. USZero
    1. USJLagana
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. POFastest way to crop an image without exceeding image dimensions in Matlab
      1. This table or related slice is empty.
      1. VTApproveEditSuggestion
    2. VO
      singulars
      1. POFastest way to crop an image without exceeding image dimensions in Matlab
      1. This table or related slice is empty.
      1. VTUpMod
    1. CO[-10 , -10 ; 1000 , 1000] is not clear. Can you give a proper example?
      singulars
      1. POFastest way to crop an image without exceeding image dimensions in Matlab
      1. USZero
    2. COSuppose the image "i" is a 400x400 image. Then the ROI specified by `[-10, 1 ; 400 , 400]` would have the topleft pixel not in the image (since it would be at position -10,1)! For my purposes, when this happens, the topleft pixel should be considered at the 1,1 position. The same reasoning holds for the bottomright pixel (if its position is beyond the boundaries of the image).
      singulars
      1. POFastest way to crop an image without exceeding image dimensions in Matlab
      1. USJLagana
    3. CODo you have the image processing toolbox? `imcrop` can take a crop rectangle as an argument and you can use `rectint` to find the intersection between the ROI and a rectangle for the whole image, i.e. [1 1 MaxWidth MaxHeight]. Don't know how fast it is though.
      singulars
      1. POFastest way to crop an image without exceeding image dimensions in Matlab
      1. USBjoernH
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload