How are textures rendered?

edit

I am interested in how textures are rendered and used in Gazebo. For example, I use the following SDF to render a textured heightmap:

<model name="heightmap">
  <static>true</static>
  <link name="height">
    <collision name="collision">
      <geometry>
        <heightmap>
          <uri>file://media/materials/textures/wasatch_calls_fort_canyon/mtn_height.jpg</uri>
          <size>380 380 201</size>
          <pos>0 0 0</pos>
        </heightmap>
      </geometry>
    </collision>
    <visual name="visual_abcedf">
      <geometry>
        <heightmap>
          <use_terrain_paging>false</use_terrain_paging>
          <texture>
            <diffuse>file://media/materials/textures/wasatch_calls_fort_canyon/texture_trimmed.png</diffuse>
            <normal>file://media/materials/textures/flat_normal.png</normal>
            <size>380</size>
          </texture>
          <uri>file://media/materials/textures/wasatch_calls_fort_canyon/mtn_height.jpg</uri>
          <size>380 380 211</size>
          <pos>0 0 0</pos>
        </heightmap>
      </geometry>
    </visual>
  </link>
</model>

I then run a drone containing a camera looking down at the ground from a set altitude. The captured image is different than the original .jpg image (texture_trimmed.jpg)in the following ways:

1. It is significantly darker.
2. There is also a small amount of blurring. I realize I am taking a picture of a picture, but the size of the texture is about 4kx4k and the size of the camera image is 2048x350, and I have matched the field of view of the camera so that it covers a little more than half of the texture, so the pixel resolution should approximately match. Is interpolation used?
3. There seems to be a small amount of distortion. This begs the question: does Gazebo assume the texture is an orthographic projection, or a projective view? I would like the textured heightmap to be created as a orthographic image laid down on the heightmap. The camera then takes a projective view of the textured heightmap, as a real camera above terrain would. Is this what Gazebo models?

I would really like to understand the answers to these questions, but the first is the most important at this time.

Thanks.