[Octave-patch-tracker] [patch #9281] Image package: imsharpen

[Hartmut]

Follow-up Comment #4, patch #9281 (project octave):

The new version of the m-file seems to have adressed all issues that popped to
my eye, originally (see comment #1). The file looks alright to me know (but I
haven't done any systematic comparison with Matlab results.) Let's wait for
Carne's feedback now.

Regarding the "new problem" (at the end of comment #3): I think you should use
im2double(I) instead of double(I) here. But when I do this, it doesn't change
any test results at all. I think that rgb2lab does this type conversion
internally already, so there is no need to do it once again in imsharpen.m

Are the remaining differences to Matlab results always of magnitude +1? Maybe
Matlab does some special treatment here, and adds a (non-standard) +1 values
somewhere? If this is really the case, would we like to do this as well, or
better stick to the text book version (without any +1 deal)? Or do you know
any reliable source to justify a +1 special treatment during an "unsharp
masking" algorithm?

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