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Color... (Top Image)

False color scales, such as the thermal scale or thresholding, are done with sliders. These affect the LUT (color look up table) of the front level image, directly under which the slider will appear. The color scale can be transferred to other images using the LUT...copy button.

Alternatively, the Color... button in the Images collumn will affect all of the selected windows at once. It will appear directly under the front image window.

Change the slider settings by dragging the small circles on either end of the colored bar.

The three top items select a LUT (look up table) for a gray scale image. 

The top four sliders are two point sliders, for normal contrast enhancement and thresholding.

The 3 point thermal slider is for enhancement in both dark and light image areas.

Gray Scale LUT

This resets the LUT (look up table) to the normal gray scale.

directional palette LUT

For use with displaying direction of gradient images, that is image where the gray level corresponds to an angle. There is an abrupt change from white to black as the angle changes from 360° to 0°, which this palette avoids, by displaying these values in a natural way: The prefered direction, chosen with the mouse - circle - rubber band window, is white. The opposite direction is black, and intermediate directions, going either CCW or CW, are intermediate shades of gray.

This is intended for use with displaying direction of gradient images, such as made with the {MLx - pixel array ops - special - DOG255}.

The prefered direction, or the 'apparent illumination direction', can be changed by using the box at the bottom with a circle and rubber band line. Click to change the direction. Use command-click to stop the rubber banding.

Copy LUT

This copies the LUT (color look up table, or palette) from the front image window to other image windows.

Two Point Sliders

The four two point sliders are really four manifestations of one slider that can act in four different modes:

  1. Threshold slider. - red color bar
  2. Thermal slider. - orangle color bar
  3. Contrast slider. - gray color bar
  4. CCH (CHI) thermal slider. - yellow color bar

All of the modes modify and use two intensity levels - a lower and upper threshold.

You can make more than one slider for one window. The effect in the window will be from the last slider clicked. Clicking on any window moves it to the front.

The title for the slider window is the title of the image window with a '.' or period on each side. The slider windows are listed in the Windows menu, not in the W menu.

The slider can be 'popped' if it becomes buried by moving the image window slightly by mousing the title bar. The reverse is also true - if you see the slider for a window but don't see the window, just drag the slider window a small distance and the image window will 'pop' to the front - perhaps on top of the slider. Once the slider window (tool) is made, it can be used at any time. To use:

Threshold slider. top

The threshold slider is a device for setting thresholds for a gray level image in order to segment it into object and background. This tool does applys a false color (red) to the image, to show the pixels selected by the threshold setting, that is, those pixels with values equal to and between the thresholds.

The slider will appear underneath the window, if screen room allows. If a Hist1 histogram is used, the slider values will be reflected in it.

The quickest way to compare the thresolded image with the original is to double click on the slider.

This tool is used to make a mask for blobbing, using the {MLx - masks - from slider} menu. The mask image is made from the SCALED image, not the original data, since it is the scaled image that you are looking at when you use the slider. (What you SEE is what you get.)


Contrast slider.

Contrast enhancement using gray levels.

Thermal slider.

Contrast enhancement using the thermal (black body) scale.

Three Point Thermal Slider.

The three point slider enhances the contrast of images in two stages that can be set independently. The first stage ramps from black to red, and is used to enhance contrast in dark image areas. The second stage ramps from red to white, and is used to enhance the bright image areas.

An example of enhancement using the three point thermal slider is this Focused Ion Beam image (which causes damage to the crystalline structures) image of a Via - metal to substrate contact. courtesy of John Hunt, Gatan Corp, Pleasanton, CA.

This is a transmission micrograph of a contact on an IC chip. The dark area on the left is a metal wire, and the area on the right is the silicon substrate. Detail in the contact is obscured because it is dark - the metal is more electron dense than the silicon.

If the contrast of the wire is increased, contrast of the substrate is lost - here is an example using a thermal scale (which generally has a wider dynamic range than a gray level scale).

Slider for above image:

The left point needs to stay near zero because much of the detail is very dark. The right point is at 161 (all intensities from 161 - 255 are shown as white), which is mid way between showing more detail in the metal and completely loosing detail in the substrate.


The result with the three point slider looks like this:

and the slider looks like this: .

The black and white points are analogous to the left and right circles at the ends of the two point slider above - they determin the value in the image to be shown as black and white respectively.

The red point determines the value that will be shown as bright red, so that values between the black and red points are ramped linearly (using only the red gun in the CRT) from black to red. Here, this color range enhances the rather narrow and low valued numerical range of the detail in the wire. The values between the red and white points are ramped from red to white as is done in the thermal scale: the green gun is ramped from 0 to max starting at the red point, and ending half way to the white point. From this mid way point, on to the white point, the blue gun is ramped from 0 to max. If the red point is positioned one third of the way from the black point to the red point, the LUT is the same as the 2 pt thermal scale, with its circles set to the black and white point values.

The motivation for making this color scale was the 'look' of the above image when enhanced by showing it as an RGB composite, with one color (channel) enhanced in the normal way to show detail in the wire, and the other two color (channels) enhanced to show detail in the substrate. The composite image had much the look of this thermal scale.

Here are some observations:

  1. Ramping one primary color independently (such as red), and then ramping the other two, gives a gain in the intensity range for perceived contrast, over ramping all three primary colors in sequence.
  2. Ramping all three colors independently - that is, making a four point slider - should not improve the situation much. Detail can be seen ramping red alone (just show a gray level image in red), or starting with red, and ramping the other two (use the CCH-thermal slider). However, when two of the three primary colors are ramped to maximum, not much detail can be seen when ramping the third, that is in the yellow - white transition.
  3. Ramping red, then green, then blue in the traditional thermal scale sequence, gives the most natural results. I tried all of the other combinations (such as Blue, green, red), but none seemed worth implementing.