An example for cuda median filter.
Tche LIU, seistche@gmail.com, USTC
Firstly, there are two way to calculate the median of filtering window in the program, respectively corresponding to the two functions medianBubble and medianNoSort in the file kernelMedianFilter.cu. The former [Bubble] uses the incomplete bubble sorting method to find the meidan, while the latter [NoSort] does not sort the input array (To be honest, I do not know what the name of the latter algorithm is, and will be grateful to you if you tell me the answer).
Besides, according to Boundary issues of the page, there are three schemes to handle missing window entries at the boundaries:
- [Discard] Avoid processing the boundaries,
- [Shrink] Shrink the window near the boundaries,
- [Extend] Repeat the first value, as with the last value.
And I have another idea for this issues, that is:
- [Zero] Fill the parts beyond the boundaries of filtering window with zero.
Finally, due to JackOLantern's answer and conclusion for the question, "the version not using shared memory seems to be (slightly) convenient in all the cases", the program replaces shared memory with register to store the filtering window.
There are some different macros for these different methods, that is, for these different functions in the file kernelMedianFilter.cu:
| Macro | Function |
|---|---|
| Bubble | medianBubble |
| NoSort | medianNoSort |
| Discard | kernelFilterDiscard |
| Extend | kernelFilterExtend |
| Shrink | kernelFilterShrink |
| Zero | kernelFilterZero |
And for extendibility, the another macro HSM is provided as half of filtering window length (FWL), i. e.,
We can arbitrarily combine Bubble/NoSort for the median calculation with Discard/Extend/Shrink/Zero for the boundary issue.
For example, if we want to filter by the former way of the median calculation, by the first scheme of the boundary issue, and with a 9x9 window, the program can be compiled with:
nvcc Main.cu -DBubble -DDiscard -DHSM=4 -o filterAnd note the setting
There are a
fp = fopen('example/data_orig.bin', 'rb');
orig = fread(fp, [600, 600], 'single');
fclose(fp);
pcolor(orig);
set(gca, 'FontSize', 20);
shading interp;
caxis([-5000,5000]);
colormap jet;
axis image;
colorbar;shown as follows:
As an example, the result of Bubble-Discard-HSM=4 for the data is:
and other results are listed below the folder figures/.
The elapsed times for different combinations are shown as follows:
And for clarity, the result based on the logarithmic time axis is as:
