Lookup table with different spacing between entries

This is a discussion on Lookup table with different spacing between entries within the C++ Programming forums, part of the General Programming Boards category; Here's my problem: I'm trying to write a program to modify gamma corrected images, but the gamma correction (which involves ...

  1. #1
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    Lookup table with different spacing between entries

    Here's my problem: I'm trying to write a program to modify gamma corrected images, but the gamma correction (which involves an RGB value, an unsigned char, to the power 2.5, or a gamma corrected value, a double, to the power 0.4) is currently taking most of the time, so I want to patch in a lookup table to speed things up. For exponentiating an unsigned char this is easy because there's only 256 possible values. Converting back can use the same table, but the best I can come up with is looping through the entire table, comparing the input with the values in the table to check what integer value is the correct answer. (luckily it's a monotonously increasing function)
    What would be a quick way to go about this? Is there perhaps a container in the STL that can do something like this?
    Typing stuff in Code::Blocks 8.02, compiling stuff with MinGW 3.4.5.

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    It's monotonic, so the data is sorted; why not do binary search?

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    Oops, probably should've figured that out myself...
    Got it to work now, thanks!
    Typing stuff in Code::Blocks 8.02, compiling stuff with MinGW 3.4.5.

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