OpenSceneGraph/OpenGL Image internalFormat

Question

I need to pass a 2D texture array to a fragment shader that performs texelFetch and bitwise operations over uchar elements.

For this reason, I need to create a texture with a very specific internal format, that guarantees that my texels are in unsigned byte integer, and that no scaling operations not casting to float is performed.

I already have my image buffers in generic uint8_t* arrays.

So I am doing this:

osg::Texture2DArray texture = new osg::Texture2DArray;
for (int i = 0; i < ntextures; i++) {
  osg::Image* image = new osg::Image( 
    textureWidth, 
    256, 
    1,
    GL_R8UI, // Texture Internal Format
    GL_RED_INTEGER, // Pixel Format
    GL_UNSIGNED_BYTE, // Pixel Type
    imageBufferPtr[i]);

  texture->setImage(i, image);
}

The previous code yeilds Invalid operation errors in the OpenGL pipeline.

On the other hand, if I do

osg::Image* image = new osg::Image( 
    textureWidth, 
    256, 
    1,
    GL_LUMINANCE, // Texture Internal Format
    GL_LUMINANCE, // Pixel Format
    GL_UNSIGNED_BYTE, // Pixel Type
    imageBufferPtr[i]);

yields no errors, but my texture gets corrupted somehow (some cast operations are probably performed).

How can I solve this?

I am ensuring that no texture resizing to power of 2 is performed.

Extra

This is my fragment shader

        #version 130 
        #extension GL_EXT_texture_array : enable

        in vec4 texcoord;

        uniform uint            width;
        uniform uint            height;
        uniform usampler2DArray textureA;

        void main() {
            uint x = uint(texcoord.x * float(width));
            uint y = uint(texcoord.y * float(height));
            uint shift = x % 8u;
            uint mask =  1u << shift;
            uint octet = texelFetch(textureA, ivec3(x / 8u, y % 256u,y / 256u), 0).r;
            uint value = (octet & mask) >> shift;
            if (value > 0u)
              gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);
            else
              gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
        }