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## Lab: Contrast Phenomena / Image Framing

[Exercises] [Workspace]

Purpose: The purpose of this lab is to gain a practical understanding the visual phenomena known as simultaneous contrast effect. The lab uses the Constant, Inset, and Pad operators to build an image that exhibits this phenomena.

Activities:

1. Create the image described below. This image exhibits the simultaneous contrast effect.

   IMAGE: The image is a square image with 4 quadrants. Each quadrant is composed of a 32x32 pixel region of constant value 160 centered in a 64x64 pixel region of constant value (Upper left quadrant = 30, Upper right quadrant = 60, Lower left quadrant = 120, Lower right quadrant = 240). There are several ways to build an image to demonstrate the simultaneous contrast effect. Described below is a procedure using the Pad and Inset operators.

   1. Create a constant image with dimensions 32x32 with grey-level value 160, using the operator Constant.

      1. Glyphs:Input/Output:Generate Data:Constant
      2. Open the Constant pane and set "Width" and "Height" to 32, and "Real Constant Level" to 160.

   2. Create four images, each one having dimensions 64x64 with values 30, 60, 120, and 240 respectively, with the image created in part A placed at its center. Use the Pad operator as follows.

      1. Glyphs:Data Manip:Size & Region Operators:Pad (just get 1)
      2. Set up the Pad operator to create a 64x64 pixel image, with the pad value of 30. Set the offsets so that the 32x32 pixel input image is centered.
      3. Use the duplicate feature in cantata to duplicate the Pad operator 3 times.
      4. Change the "Real Pad Value" in the other three Pad operators to 60, 120, and 240.
      5. Connect the output of the Constant operator to the inputs of the Pad operators.

   3. Use three Inset operators and the four images created in part B to create a new square image that contains all four images. Display the final image.

      1. Glyphs:Data Manip:Size & Region Operators:Inset
      2. Glyphs:Visualization:Non-Interactive Display:Display Image
      3. Set the Inset "Width Coordinate" to 64.
      4. Duplicate the Inset operator.
      5. Connect the output of the first and second Pad operators to the inputs of the first Inset operator.
      6. Connect the output of the third and fourth Pad operators to the inputs of the second Inset operator.
      7. Duplicate an Inset operator and change the "Width Coordinate" to 0 and the "Height Coordinate" to 64.
      8. Connect the output from the first and second Inset operators to the third "Inset" operator.
      9. Connect the output of the third Inset operator to the Display Image operator and run the workspace.

Exercises

1. Create your Pad operator using the operators Constant and Inset
2. Propose two ways of using the Inset operator to combine four images into a larger square.
3. Experiment with the simultaneous contrast phenomena by changing the intensity values of the centered box and the background.

Khoros Workspace
Execute the visual program c2s6contrast-hvs.wk