3 ms·

can you expand on why RGB wouldn't work? The most obvious way I can think of to include chroma information in apriltags would be to use 3 colors matched to the

• lettergram 10y ago
  The RGB color space works, it just has light encoded in each channel (making it unnormalized). Separating out the light, i.e. normalizing on the color is what gives LAB the advantage. Further, because the way RGB is structured taking the difference between channels is more difficult (requires more calculations) than it does for the a & b channels. For instance, the a channel represents red to green, or positive a represents red and negative a represents green. This aids in finding edges between red and green with a simple addition/subtraction between pixels(a[i,i] - a[j,j]). If we were to try the same thing in the RGB space it would look something like (R[i,i] + G[i,i]) - (R[j,j] + G[j,j]), and you would still have the impact of light to deal with...
• jamessb 10y ago
  There has been previous work that was similar to what I think you mean (and predates AprilTags) [1]. The idea is to use markers that are grids, with each cell colored either red, green or blue; tag detection is then done by finding the rectangular region of the image over which the average of the RGB contrast function [2] is maximised. Thus tags are detected based on color without having to do edge detection across the whole image. [1]: http://www.alexwg.org/publications/ProcSPIE_6623-662304.pdf http://www.alexwg.org/publications/ProcSPIE_6623-662304.pdf [2]: at a single pixel, this is sqrt((r-g)^2 + (g-b)^2 + (r-b)^2))