If data have been loaded into the program as 16-bit integers instead of bytes, they are first converted to bytes using the scaling determined by the the Low and High sliders in the Information window. For best results, be sure that the Low and High sliders are set so that images have a good contrast with a fairly wide range between the Black and White sliders. Using the autocontrast function generally leaves the sliders in positions that will allow good scaling for display. Changing the Low and High sliders will change the contrast of this image display.

The first three check boxes (X, Y, and Z in Image plane to show) turn on the display of the indicated image planes. The hot key Z or Shift+Z will turn the Z image on or off, while Shift+X and Shift+Y will toggle the X and Y image planes.

The X, Y, and Z checkboxes inside Clip model near plane in enable a display of a portion of the model just on or near the displayed plane. It sets up clipping planes on each side of the selected image slice to restrict what portion of the model appears. The clip plane on the back side is right up against the image plane and the plane on the front can be offset from the image plane. The Gap: spin box entry sets the gap between the clipping planes, which corresponds to how many extra slices of model appear. In addition, if you step the spin box below 0, it is equivalent to setting an infinite gap; i.e., the entire model on one side of the plane will appear. The spin box will show "uni" for unidirectional. Note these points:

• If you try to clip on more than one axis, most likely no model will show up, or very little.
• This feature does not work properly with transparency or drawing of multiple image planes.
• Display of contours is good in Z planes but likely to be problematic in X and Y planes, unless there are contours drawn in those planes in the Slicer. A mesh may display better, but might need to be lit on both sides.
• The number of clipping planes is limited, probably to 6 or 8, and the two planes needed for this feature are added last. Thus if the number planes ordinarily being applied for a given object (the sum of object and global planes, if any) reaches this limit, this feature will not work for that object.

  The X, Y, and Z sliders will track the current point coordinate in 3dmod image display windows and can be used to adjust both the current point position and the displayed slice in the model view window.

  The X size, Y size, and Z size sliders can be used to set the size of the image that is displayed in each dimension. The displayed area will be centered on the coordinate unless that would result in the displayed size being smaller than the slider value.

  The # of slices slider can be used to display multiple slices. You will be able to see through to the last slice but not past the slices, unless you turn on transparency.

  Use the Transparency slider to see through the image.

  The Black Level and White Level sliders can be used to adjust the contrast of the image. You can reverse the contrast by making Black be higher than White.

  Press Use 3dmod Black/White to set these level sliders from the current values of the Black and White sliders in the 3dmod Information window.

  The False color checkbox allows images to be displayed in the standard false color scheme. It does not appear if color images are loaded.

  Turn on the Apply global clip planes checkbox to have the image clipped with the global clipping planes, if any are turned on.

  The Use antialiased reduction checkbox controls whether an antialiasing filter is used for displaying images at scales under 0.75. For a very large image (e.g., > 10K x 10K), producing the filtered image can take a significant amount of time, but it is only a small fraction of the total time for drawing large images. Use the X and Y size sliders to reduce the time for drawing images much larger than fits in the window.

  The Fill button appears at the bottom if 3dmod is opened with an image pyramid and can be used to load data into the cache for the currently displayed region. This may be necessary to get a complete display of X or Y planes. When the zoom is below 1, lower resolution data are accessed if available.

  Limitations of transparency: Image transparency, model object transparency, and the display of multiple slices all use a similar method for generating transparency. Displays will often not work well when you have more than one item that relies on this transparency method, because the items are not being drawn in order from back to front everywhere that they overlap. In particular, if you are displaying multiple slices, you will need to introduce significant image transparency to see any transparent objects. You may then need to adjust the black and white level sliders in this dialog to compensate for the resulting change in brightness or contrast of the image data.

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