Andy Li's Blog

There is bilinear resampling by Pixel Bender already, why not bicubic too?

With the very helpful Java implementation, I can get bicubic resampling running in Pixel Bender in hours.

Here is my result, along with the resampling results in PhotoShop as a comparison:

Source image (size 4x4, scaled by your browser) Source image enlarged by PS (nearest neighbor) Bicubic resampling by Pixel Bender

There is some difference with PhotoShop’s versions (below), hope it’s not my mistake…

Bicubic resampling by PhotoShop. Bicubic smoother by PhotoShop Bicubic sharper by PhotoShop

My codes can be downloaded below:
Bicubic resampling sample program source (with PB source)

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Update:
Notified by author of the Java version, the Java code was wrong and has been updated. Here below is my updated code:
Bicubic resampling sample program source (with PB source)

While traveling with my gf in Europe, I’m planning to develop a better technique to use color marker in FLARtoolkit (which I’ve tried before).

For the first step of doing so is to find a algorithm of matching colors. Using blend mode “difference” on the image is not flexible and may not fit all situations. I decided to calculate the difference by comparing hue, saturation and brightness of the colors and then threshold the image.

This is very similar to (if not exactly) doing chroma key. Maybe there is some awesome beautiful chroma key algorithm but I can’t find a fast and flexible enough to do so. If you know one, please tell me.

One problem I faced is choosing between color space models. RGB surely wouldn’t be the choice since it do not give hue value directly. There are HSV and HSL I found to be quite suitable. The two models share the same algorithm to calculate hue but have different ones for saturation and brightness. After reading the algorithms, my decision is… try both.

Another problem is how to preform thresholding. First method is after calculating the pixel difference, add the difference in hue, saturation and brightness altogether with weightings and do a one-time threshold to the gray-scale image. Second method is calculate the difference and give threshold limits to the three channels (H,S,V or H,S,L), only the pixels pass all the three thresholds will be white. First method should be more easily to incorporate with other filters developed for AR (like the very hot adaptive thresholding), but the second method can be more precise.  Finally I tried both too…

Here is the result. While I have set some default values to the filters, be sure to play around with the values when you change the target color. There wouldn’t be a set of values that fits all methods and situations.

I’ll try integrate it with FLARtoolkit and release the source when it is ready, be sure to check back soon.

Update:
Source and new demo is here!