The Image Object and Its Properties - MATLAB & Simulink - MathWorks Deutschland (2024)

Note

The image and imagesc commands createimage objects. Image objects are children of axes objects, as are line, patch,surface, and text objects. Like all graphics objects, the image object has anumber of properties you can set to fine-tune its appearance on the screen. Themost important properties of the image object with respect to appearance areCData, CDataMapping,XData, and YData. These properties arediscussed in this and the following sections. For detailed information aboutthese and all the properties of the image object, see image.

h = image(X); colormap(map)Y = get(h,'CData');

h = image(X); colormap(map)get(h,'CDataMapping')ans =direct

h = imagesc(I,[0 1]); colormap(map)get(h,'CDataMapping')ans =scaledget(gca,'CLim')ans =[0 1]

• The left column of the image has an x-coordinateof 1.

• The right column of the image has an x-coordinateof n.

• The top row of the image has a y-coordinateof 1.

• The bottom row of the image has a y-coordinateof m.

• Use the smallest data type possible. Using a uint8 data type for your image will be faster than using a double data type.

  Part of the process of setting the image's CData property includes copying the matrix for the image's use. The overall size of the matrix is dependent on the size of its individual elements. Using smaller individual elements (i.e., a smaller data type) decreases matrix size, and reduces the amount of time needed to copy the matrix.

• Use the smallest acceptable matrix.

  If the speed at which the image is displayed is your highest priority, you may need to compromise on the size and quality of the image. Again, decreasing the size reduces the time needed to copy the matrix.

• Set the limit mode properties (XLimMode and YLimMode) of your axes to manual.

  If they are set to auto, then every time an object (such as an image, line, patch, etc.) changes some aspect of its data, the axes must recalculate its related properties. For example, if you specify

  image(firstimage);set(gca, 'xlimmode','manual',...'ylimmode','manual',...'zlimmode','manual',...'climmode','manual',...'alimmode','manual');

  the axes do not recalculate any of the limit values before redrawing the image.

• Consider using a movie object if the main point of your task is to simply display a series of images onscreen.

  The MATLAB^® movie object utilizes underlying system graphics resources directly, instead of executing MATLAB object code. This is faster than repeatedly setting an image's CData property, as described earlier.