getting pixel data from image using libpng

This is a discussion on getting pixel data from image using libpng within the C Programming forums, part of the General Programming Boards category; I am trying for create a program that performs 2-dimensional fast fourier transforms on each pixel of data in an ...

  1. #1
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    getting pixel data from image using libpng

    I am trying for create a program that performs 2-dimensional fast fourier transforms on each pixel of data in an image. I am going to transform each channel seperately, then map the coefficients to colours and recombine them into an image.

    But I cannot seem to figure out how to read/interpret the pixel data using libpng. Can someone help me find out how I would read a png image and read each pixel's data into an array?

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    We don't work quite that way.

    YOU show US what you've done to try to solve the problem, and where you're stuck - with code, preferably.

    When we see code that you're working with, we can be specific. Without it, we can't be specific.

    Is your file a PNG file? Did you read up on it's format? Did you look at it's contents with a Hex Editor? How did you open the file? What kind of variables did you use?

    See what I mean?

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    I don't really have code to show you that would be of any help. But I can be more specific with the nature of my problem.

    My program reads in a PNG file and I can fetch it's width and height from the info structure. I also know how to read each row into an array of type png_bytep. I have no idea how I am supposed to access the individual color components of each pixel from the byte array though. I apologize for my vague description initially, I am just new to this particular library, and it's common usage is apparently quite different than what I am attemping to use it for.

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    Captain Crash brewbuck's Avatar
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    If the pixels are 24-bit RGB, then the data is composed of interleaved and repeating R, G, and B samples. R comes first, then G, then B.

    Code:
    unsigned char *red = (unsigned char *)ptrToRow[ Y ] + 3 * X;
    unsigned char *green = (unsigned char *)ptrToRow[ Y ] + 3 * X + 1;
    unsigned char *blue = (unsigned char *)ptrToRow[ Y ] + 3 * X + 2;
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

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    Thank you very much.

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    Registered User rogster001's Avatar
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    this is a good article, though it is SDL >

    Lazy Foo' Productions

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