Additional Techniques for Fast Image Updating :: Displaying Bit-Mapped Images (Graphics)

Graphics

Additional Techniques for Fast Image Updating

To increase the rate at which MATLAB can update the CData property of an image object you can optimize CData and set some related figure and axes properties:

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

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 datatype) 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 will reduce the time needed to copy the matrix.

Make the axes exactly the same size (in pixels) as the CData matrix.

Maintaining a one-to-one correspondence between the data and the onscreen pixels will eliminate the need for interpolation. For example:
- ```
set(gca,'Units','pixels')
pos = get(gca,'Position')
width = pos(3);
height = pos(4);
```
When the size of your CData exactly equals [width height], each element of the array corresponds directly to a pixel. Otherwise, MATLAB must interpolate the values in the "CData" array, so it will fit the axes at their current size.

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 will not recalculate any of the limit values before redrawing the image.

Set the figure's DoubleBuffer property to off.

```
set(gcf,'doublebuffer','off');
```

Set the DoubleBuffer property on for to obtain flicker-free animation. However, to maximize rendering speed, set DoubleBuffer to off.

Alternately, you might 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 gexecuting MATLAB object code. This is faster than repeatedly setting an image's CData property, as outlined above.

EraseMode Printing Images