Warp

Corrects (or adds) distortion in the image.

1-D warp

1. Select a series of control points to define the distortion to be corrected. For example, if you have an SDS gel in which the bands are U-shaped, trace out a U-shaped curve somewhere on the image that follows the U shape.
2. Press any key. This fixes the curve in place (it becomes invisible).
3. (Vertical warping only) With the mouse, select a y-value somewhere below the lowest point in the curve which you traced out.
4. Click the left mouse button at the desired y-value.
5. Each vertical line on the screen will be shifted up or down so that each point on the curve you traced out is lined up with the selected y-value.

Horizontal warping is similar, except that the pixels are shifted left and right to create a ripple distortion effect similar to a reflection in water. The height of the curve you trace with the mouse determines the distance by which the pixels at the corresponding x coordinate are shifted. (Upleft, down=right).

2-D warp

Clicking on ``2-D warp'' creates a new copy of the image with a square grid. Click on the grid vertices and drag to distort the image in 2 dimensions. When finished, pressing Esc or clicking the main Cancel button will erase the grid lines and return to normal mode.

Pixels/grid point: selects the spacing between grid points.

Commands available while warping is active:

• c Makes a copy of the warped image. Warping then continues, making it easy to create multi-frame images with different amounts of warping (see example below).
• g Toggles the grid lines on/off. Warping is still possible.
• r Causes the grid to revert back to its original square shape.
• Esc Press Esc or click the main cancel button when finished.

Example of several frames created by pressing `c' during 2D warping, showing increasing degrees of distortion to the original image.

Tips on 2D warping

1. Grid lines should not cross each other. This can cause discontinuities in the warped image. If a large displacement is needed, move the adjoining grid points as well to prevent this.
2. Speed can be increased by turning grid lines off. Even though the grid lines are not visible, the individual displacements still should be small enough to prevent the control points from crossing. Also, extreme displacements can cause an unnaturally smooth appearance due to replication of adjacent source pixels.
3. Individual grids should be kept as rectangular as possible to preserve spatial relationships within features.
4. Images should not be deleted during warping. If the original image or warped image are deleted during warping, an error message is displayed.
5. Future versions of tnimage will be able to move sets of grid points simultaneously instead of one at a time.