Fork of https://gist.github.com/SurpriseTRex/10633830 showing some further revisions possible. Original description: Nuke script. Down-rezzes and re-draws the selected read node in the Node Graph, using Constant nodes as pixels. Accounts for aspect ratio. More than 20x20 not recommended for performance reasons.

constantDraw.py

__author__ = 'SurpriseTRex'


def draw_constant(res=10):
    """Re-draws a Read node using Constant nodes as pixels."""
    # Checks that the user has selected a Read node.

    try:
        node = nuke.selectedNode()
    except ValueError:
        nuke.message("No node selected!")
        return False
    else:
        if node.Class() != "Read":
            # Pushes pop up message to the user
            nuke.message("No Read node selected to re-draw!")
            return False
    
    # Sets the Image Height/Width.
    imgHeight = node.height()
    imgWidth = node.width()
    # Sets the Node Grid Height/Width, making sure to maintain Aspect Ratio.
    gridHeight = res
    gridWidth = res * imgWidth / imgHeight

    # The loops construct the grid layout of the pixels.
    for y in xrange(gridHeight):
        for x in xrange(gridWidth):
            # Construct the Constant nodes and set their position.
            c = nuke.nodes.Constant(xpos=x * 70, ypos=-y * 70)
            # Get our sample position
            sampleX = 0.5 + (x * (imgWidth / gridWidth))
            sampleY = 0.5 + (y * (imgHeight / gridHeight))
            # Generate a list of rgba values at sample position
            colorValues = [
                nuke.sample(
                    node,
                    color,
                    sampleX,
                    sampleY
                ) for color in ['r', 'g', 'b', 'a']]
            # Sets Constant colour to sampled pixels.
            c['color'].setValue(colorValues)