Object Graphics Programs

The are programs written in the object graphics system.

CONTRASTZOOM Allows "in place" zoomimg and interactive contrast/brightness adjustment using object graphics.
FSC_PLOTWINDOW A "good-for-nothing-yet" object compound widget program, written with object graphics.
HCOLORBAR Create object graphics horizontal color bar.
IMAGE_BLEND Image with transparent image overlay.
IXYOUTS A program, analogous to XYOUTS, for adding text to iTools.
OBJECT_SHADE_SURF Elevation-shaded surface in object graphics.
REVERSE_AXES Demonstrates how to reverse object graphics axes.
SELECT_OBJECTS Select and move objects interactively.
SIMPLE_SURFACE A much simplified cgSURFACE object program.
TEXTURE_SURFACE A program that demonstrates the proper way to overlay an image on a surface object.
VCOLORBAR Creates object graphics vertical color bar.
ZOOMBOX Zooms into image with rubberband selection technique. (Uses object graphics.)

CONTRASTZOOM

This is an object graphics program that I set as a programming exercise for myself. I had several ideas I wanted to work out in object graphics. First, I wanted to know how to work with several graphical representations of data in the same graphics window. I wanted each view to work independently of the others, and I wanted to know how to gather user interaction from each view. Second, I wanted to know how to do an "in place" zoom into an image, and do it in such a way that I could preserve the aspect ratio of the portion of the image I was zooming into. Third, I wanted to show how to "window" and "level" an image. This is also known as setting the "contrast" and "brightness" of the image. I wanted to do this in conjunction with a color bar that reflected the window and level in a way that was intuitive and gave me a sense that I knew what I was doing. :-)

I spent nearly 10 days working on this. Not exclusively, but steadily. I was surprised at how difficult it was to get what I wanted. The IDL documentation does not offer much in the way of how to do things easily. For example, I tried several different ways of drawing the rubberband box in the zoom image until I found a method that reliably gave me the proper image coordinates. It took me a long time to figure out how to maintain the proper aspect ratio of the image in a resizeable graphics window. At the end, I got fairly good at knowing what to do. But I spent hours staring at my computer screen, too.

You can see a picture of the program in the figure below. The left image is a zoomable image. Click and drag a rubberband box around the portion of the image you wish to "zoom" into. The image is not necessarily zoomed. Rather, this portion of the image is shown in the graphics view in a way that preserves its aspect ratio. The effect is to have it appear that you are zooming into the data. To "zoom out" to the entire image, just click and release anywhere in the left window.

The center window is the contrast/brightness image. Click and drag the cursor horizontally in this window to adjust the "brightness" or "level" of the image data. Click and drag the cursor vertically in this window to adjust the "contrast" or "window" into the image data. Click and release the cursor in this window to return to the starting values of 25% contrast and 75% brightness.

	FSC_PLOTWINDOW
	This is an object compound widget, written using object graphics, that is -- quite frankly -- probably not good for much of anything, except curiosity. I use it to good effect in my FSC_PSConfig program. It consists of a resizeable "plot" window inside a draw widget. If I come up with any more uses for it, I'll let you know. :-)

	HCOLORBAR
	This is a program that creates a horizontal colorbar using IDL object graphics. This program defines the methods and structure for a horizontal colorbar object. The program should be named "hcolorbar__define.pro". This program shows you the correct way to create your own object graphics primitive from a collection of objects from the IDL object graphics class library.

IMAGE_BLEND

People have asked for the best way to combine two images so that you could see through one image into the other. This is one way to do it, using the alpha blending channel available with object graphics images. In the default mode, you can overlay a color image on a gray-scale image. But this program is written so that you can change both the foreground and background image colors and set the "amount" of transparency with a slider.

	iXYOUTS
	This is a program for adding text to an iTool program interactively. It is analogous to XYOUTS in direct graphics. It can accept any keywords that are appropriate for an IDLgrTEXT object.

	OBJECT_SHADE_SURF
	Someone on the IDL newsgroup wanted to know how to make an elevation- shaded surface in object graphics. Oddly enough, you do this by turning all shading off! Here is an example of how to do it.

	REVERSE_AXES
	I was asked a simple question: "How do you reverse an object graphics axis without the textual annotation going completely bonkers." Four days later, I came up with the answer. It wasn't what I expected. You can read the details in this article. But here is the code that shows you how to do it.

SELECT_OBJECTS

This is an example program that shows you the easiest way to select, move, and size graphics objects interactively. The program displays an image, colorbar, and title object which can be selected and moved within the graphics object window. In addition, the right mouse button causes the selected object to get smaller, while the middle mouse button causes the selected object to get larger. This program requires several programs from the Coyote Library, which you can download as a zip file if you like.

	SIMPLE_SURFACE
	This is a greatly simplified version of cgSurface without all the bells and whistles of the latter program. If you are just getting started with object graphics, this is a good program to start learning from.

TEXTURE_SURFACE

If you follow the suggestions of the IDL on-line documentation for adding an image as a texture map to an object graphics surface, you will be led astray. Here is the proper way to add an image as a texture map. Details about the process can be found in this article. The program also demonstrates how to add a texture to just a portion of the surface, and how to specify a color for the remaining portion of the surface. These details are not covered at all in the IDL documentation.

	VCOLORBAR
	This is a program that creates a vertical colorbar using IDL object graphics. This program defines the methods and structure for a vertical colorbar object. The program should be named "vcolorbar__define.pro". This program shows you the correct way to create your own object graphics primitive from a collection of objects from the IDL object graphics class library.

	ZOOMBOX
	This example program is simlar to FSC_ZIMAGE, except that it is written as an object graphics program instead of as a direct graphics program. It allows you to zoom into an 8-bit or 24-bit image using a rubberband selection box technique. Various zoom factors and other features can be set via pull-down menus.

Version of IDL used to prepare this article: IDL 7.0.1.

Last Updated: 21 March 2011