Highlighting plotted points in an Image plot

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Thu, 01/17/2013 - 01:20 pm

Hi. I am using NewImage to create an image plot of a 2D matrix using a Grays color table. In my code, I would like to go through each data point in the matrix and replot certain points as red that fall under a criteria I set. Is there some sort of plot point function where I can construct an image plot point by point in a for loop or a way to recolor a particular point in an image plot that was created using NewImage?

Thanks
Satish
Hello Satish,

One approach is to display a combination of two images with one image effectively transparent except at a set of pixels that you set to red. You can find an example of this in the Image Processing Tutorial. Simply execute:

DisplayHelpTopic "Overlays and Ornaments"

A.G.
WaveMetrics, Inc.

January 17, 2013 at 02:13 pm - Permalink

Hi.
The example in the help topic works, but when I apply it to my image, the overlay whites out the portions of the original image that I am overlaying on. So I get pixels highlighted in red and then just white everywhere else. This isn't the case when I run the example in the help topic. Modifying Image Appearance dialog box still shows that it's Grays LUT and changing scale doesn't do anything.

Thanks

Satish

January 18, 2013 at 09:03 am - Permalink

skrao wrote:
The example in the help topic works, but when I apply it to my image, the overlay whites out the portions of the original image that I am overlaying on. So I get pixels highlighted in red and then just white everywhere else.


If you are getting "white everywhere else" it suggests that you have not set the level of the pixels corresponding to your "everywhere else" to 64. For more information on that execute:
DisplayHelpTopic "Images and the NaN Concept"

A.G.
WaveMetrics, Inc.

January 18, 2013 at 10:05 am - Permalink

skrao wrote:

Modifying Image Appearance dialog box still shows that it's Grays LUT and changing scale doesn't do anything.


It kind of sounds like you are looking at the display parameters for your base image rather than for the overlay in the Modify Image Appearance dialog. At the top of that dialog is a drop down box titled "Image Wave". This shows the name of the image that the parameters apply to. Try clicking on the box and selecting the overlay wave.

You will need to modify "First Color at Z =", "Last Color at Z =" and "Before First Color", "After Last Color" for the overlay image, to get the overlay transparency correct.

January 18, 2013 at 02:00 pm - Permalink