HIPR - Erratum

Known errors:

1. gsmooth (Nov 6, 1996): "effect is to remove low spatial frequency components from an image" -> "effect is to remove high spatial frequency components from an image".
2. pixlog (Nov 6, 1996): "Mapping function for exponential transform" -> "Mapping function for logarithmic transform" caption on Figure 1 (needs gif image hacking to fix).
3. affine (April 2, 1999): We did not specify that positive angles meant clockwise rotation and that we were using image coordinates with +Y being down.
4. rotate (April 2, 1999): We did not specify that positive angles meant clockwise rotation and that we were using image coordinates with +Y being down.

   Under these conditions, we get:
   x = (x_1 - x_o) cos (theta) - (y_1 - y_0) sin (theta) + x_o
   y = (x_1 - x_o) sin (theta) + (y_1 - y_0) cos (theta) + y_o
   

5. adaptive thresholding operator (Aug 27, 1999): The equation for the mean threshold should be .
6. exponential operator (July 10, 2000): The equation in the caption in Figure 1 should be .
7. line detector operator (September 22, 2000): The equation for testing the maximality of the convolution output should be .
8. Glossary entry for Pixel Connectivity (October 12, 2000): The equation for defining the 4-neighborhood should be .
9. Weights for gaussian smoothing (September 20, 2001): The weights should have been calculated by integrating over the pixel. It was unclear how they were calculated. New weights have been calculated, using a new sigma=1.0. New masks
   
   and
   
   are shown.
10. Weights for Laplacian of Gaussian mask (November 1, 2001): The weights should have been calculated by integrating over the pixel. It was unclear how they were calculated. New weights have been calculated, using a new sigma=1.4. Some value have been rounded the wrong way to preserve the zero sum property. The new mask is:
    
11. JAVA Operator Interative Exploration Under Internet Explorer (March 19, 2002): All operator interative exploration now works; however the FFT and Histogram Equalization displays have layout problems that need fixing in the future.
12. JAVA Operator Tableau median smoothing operator (July 2, 2005): Median filter in the tableau was fixed. Previously not correctly getting kernel values.
13. JAVA Connected components operator (Oct 4, 2005): Fixed to work correctly with more than 256 components.
14. Laplacian of Gaussian small mask removed (Feb 15, 2006): The 3rd small LoG mask -1,2,-1/2,-4,2/-1,2,-1 was removed as it is not a small mask approximation to the LoG.
15. Laplacian of Gaussian and Gaussian Smoothing JAVA code (March 7, 2006): Replaced for loops with this structure:
    for(double ySubPixel = y - 0.5; ySubPixel < y + 0.6; ySubPixel +=0.1)
    by this structure:
    for(double ySubPixel = y - 0.5; ySubPixel < y + 0.55; ySubPixel +=0.1)
    because some users get asymmetric masks.
16. Exponential/`Raise to Power' Operator (November 1, 2006): "As we can see from the formula, Q=0 yields P=c." should be "As we can see from the formula, P=0 yields Q=c.".
17. Logarithm Operator (November 1, 2006): "Hence, both are suitable to enhance details contained in the high values." should be "Hence, both are suitable to enhance details contained in the low values.".
18. Connected Components Labeling (Nov 15, 2006): "else if one or more of the neighbors have V={1}, assign one of the labels to p and make a note of the equivalences." -> "else if more than one of the neighbors have V={1}, assign one of the labels to p and make a note of the equivalences."
19. Fourier Transform (March 7, 2007): In the "Guidelines for Use" section the example with the vertical stripes the f_{max} should be 1/(2 pixels) because the period is really 2 pixels. Similarly, the next equation should be 1/(4 pixels).
20. Fourier Transform (Aug 23, 2007): In the "How It Works" section, the use of (i,j) for image coordinates is replaced by (a,b) because of the potential for confusion with i or j as the square root of -1.
21. Gaussian Smoothing (April 4, 2008): "mean filter with width 7" -> "mean filter with width 5".
22. Conservative Smoothing (July 21, 2008): conservative smoothing interactive demo fixed (missing executable in jar make).
23. Roberts Cross (September 14, 2009): Edge orientation estimate from arctan()-3/4 pi to arctan()+1/4 pi.
24. Fourier Transform (December 29, 2009): Clarity improved in several places by making explicit where the magnitude of the Fourier transiform is displayed.
25. Fourier Transform (February 4, 2011): Correcting 1/(N*N) normalization to appear on only inverse transform, and adding a note about about equivalence.
26. Gaussian Smoothing (June 11, 2013): Explaining in more detail how the example smoothing mask values were calculated.
27. Fourier Transform JAVA demo (March 16, 2015): Added a note about about ensuring that the images are square, otherwise the FFT may not work.
28. Hit-and-miss operator (April 21, 2016): Added mask 3c for completeness.