The Drawer

The Histogram

The histogram plots the number of pixels that have been set at each of the 256 possible gray levels.The horizontal scale is logarithmic, the first red line corresponding to 10 pixels at that gray level, the second to 100, etc.

If the screen is set to black and white the display the histogram will have a blue line across it. Those pixels above the blue line on the histogram will be presented as white those below will be black. A click on the histogram will move the blue line to a new setting and redraw the screen. The text field labeled"Cut Off" shows the level at which the blue line is set. If you enter a number into the text box from the key board, the blue line will be set to that value as soon as you use the return or tab key. You can use the black and white image produced to be entered or used the the logical actions on the "Combine" menu.

Wherever you have set the blue line you can use the "truncate from above" or "truncate from below" keys bring down all pixels above that level to the blue line, or in the case of "truncate from below" pixels are brought up to the blue line. With the exception of the "phase angle", the truncate action is on that aspect of the complex array that is being presented (real, imaginary, etc.). If "phase angle" is being displayed "truncate" has no action.

At the top of the histogram window is a box labeled "set display maximum". Checking this box reveals a text box that when a number is entered that number (exponential notation ok) the image displayed on the screen will be scaled so that that value represents the magnitude of the maximum maximum value presented. That is to say, if there is a value that large or larger it will be presented as the greatest saturation. You would use this to permit yourself to see pixel values that are small in a image full of pixels many times larger. If you have a central peak with magnetude 1000 and some feature around 0.01, you may want to set the max value to around 0.015.
I have set this up so this feature is not available when displaying the phase.
Note that this feature does not change any values in the big array, but only changes the way data is sent to the screen buffer.

The Drawing Tools

The drawing tools act as you hope they do. Select the tool and use it. The pencil tool draws a one pixel wide line on the screen, and if the shift key is held down it becomes an eraser. The narrow eraser tool next to the pencil does the opposite. The sponge draws a wide square on the screen the blue eraser below erases.

The magnifier action is to step up the magnification one step and to try to center the point at which the click occurred. Once maximum magnification occurs it just moves the click point to the center. A shift click steps down the magnification and centers the click point.

The hand in the center slides the screen about, provided that the scroll bars are displayed.

The other two hands slide the the screen with respect to itself, resulting in a wrap around. For large array sizes this is a slow process, and you should keep your eye on the coordinates and move slowly and carefully. One of the bottom hands just moves the screen, the other moves the big array. The actions look the same at first so be carefully. You can of course just put a dot on the screen and correlate the array with it using fourier transforms.