CODEWITHSUNDEEP
copengl
usernameisunavaible
usernameisunavaible

Reputation: 31

Color normalization results in gray tones

I am currently writing an raycaster and I wanted to add textures to my walls, but an color error holds me back.

I use floating point numbers in my C code to represent colors, but the graphic I am using is in the rgb byte format. I get the error when using the normalized floating point values. Loaded with the following code everything works correctly (but using the undesired rgb byte functions):

    //... glfw window initialization...
    for (int y = 0; y < 32; y++)
    {
        for (int x = 0; x < 32; x++)
        {
            int p = (y * 32 + x) * 3;
            float r = rgb[p];
            float g = rgb[p + 1];
            float b = rgb[p + 2];

            glColor3ub(r, g, b);
            glPointSize(16);
            glBegin(GL_POINTS);
            glVertex2i(x * 16, y * 16);
            glEnd();
        }
    }

Resulting in:

enter image description here

The error occurs if I try to normalize the bytes (one by one) with the following code:

    //... glfw window initialization...
    for (int y = 0; y < 32; y++)
    {
        for (int x = 0; x < 32; x++)
        {
            int p = (y * 32 + x) * 3;
            float r = ((float)rgb[p]) / 255.0f;
            float g = ((float)rgb[p + 1]) / 255.0f;
            float b = ((float)rgb[p + 2]) / 255.0f;

            glColor3f(r,g, b);
            glPointSize(16);
            glBegin(GL_POINTS);
            glVertex2i(x * 16, y * 16);
            glEnd();
        }
    }

The picture loaded this way has different colors: The wrong result

Upvotes: 0

Views: 204

Answers (1)

Weather Vane
Weather Vane

Reputation: 34585

Suppose the array rbg[] is signed, and consider a red component value 255.

In the first example the 255 is actually -1 and is converted to -1.000000 and this is then passed to the function after converting to type GLubyte which is unsigned 8-bit. The conversion rules will make this value 255 which is what you thought you had.

In the second example the 255 is again converted to -1.000000 and scaled to be -0.003922 instead of the expected 1.000000and so the result is very different from what you expected.

The solution is to define the array as unsigned char or uint8_t.

Upvotes: 4

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