I am performing image registration by extracting SURF features from 2 multi temporal satellite images, in Matlab, as explained here.
The steps provided seem to work great for me, and I can visually see that the target image is aligned correctly to the fixed image.
How do I access the accuracy of the method? In other words, is there any way to make a statement such as this "these 2 images are "XX" % aligned to each other" ?
There is not a way to get a true "XX%" answer, as discussed in the comments, unless the images are identical or you already know the answer. Other ideas:
1) You could use correlation to get a value and set a threshold for your results. (e.g., assume images with corr. coeff. > 0.8 are aligned well). Threshold depends on your data.
2) You could restrict the correlation to the immediate regions of the registration marks or features selected by the algorithm. Then assume that the registration features are identical between the two images, so that a corr. coeff. == 1.0 (mean value across all features) is perfect (100%) registration. This is likely to always be a high number, if the matching algorithm is working.
3) Pick one matched feature to exclude from the registration algorithm, and use the correlation of that region in the two images after matching as your % value. This is maybe the most rigorous method, but it requires a known feature to work with.
All the results based on correlation assume some normalization of the image data, adjusting for contrast, scale, etc.