Loading a DDS to a QImage using QGLPixelBuffer.

dds2image.cpp

QImage readDDSFile(const QString &filename)
{
    QGLWidget glWidget;
    glWidget.makeCurrent();

    GLuint texture = glWidget.bindTexture(filename);
    if (!texture)
        return QImage();

    // Determine the size of the DDS image
    GLint width, height;
    glBindTexture(GL_TEXTURE_2D, texture);
    glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_WIDTH, &width);
    glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_HEIGHT, &height);

    if (width == 0 || height == 0)
        return QImage();

    QGLPixelBuffer pbuffer(QSize(width, height), glWidget.format(), &glWidget);
    if (!pbuffer.makeCurrent())
        return QImage();

    pbuffer.drawTexture(QRectF(-1, -1, 2, 2), texture);
    return pbuffer.toImage();
}

Note: better just use the DDS image plugin shipping with Qt!