WALTER  DIONI                                                             CANCÚN, MÉXICO

Many times inadvertently, or by a technical error, a photomicrograph of an interesting subject can be spoiled by the presence of "junk" or "dust" in the background, or even superimposed on parts of the image, that you notice when it is impossible to repeat the shot.

One technique that can be used in such cases to produce photos with a cleaner background is the amalgamation of two complementary images.

** Amalgamate, is a technical term indicating the fusion of two superimposed images, producing a synthesis of both images. To do this, an image that has background defects produced by shading due to dust or other impurities in the light system, is digitally merged (amalgamated)  with a second picture taken from the same field of view having first withdrawn the object photographed. 

For the procedure to be effective the last image must be subsequently inverted. Thus, in the third image (the correction screen) the dark spots of the background will be now represented by light spots of corresponding density. By merging digitally the original image and the correction screen image with clear spots, neutralises the corresponding dark spots of the first. Usually the result is spectacular, producing a much cleaner background than the original photo. Of course junk included into the preparation (not at the background) are not removed by this method.

The existence of this technique makes it sensible to routinely take an image of the background, by displacing the slide with the subject, before photographing interesting subjects. If you do not need it, it is easy to discard. But often to the more careful photographer will escape details that are discovered later. The technique also helps, and it is not a less important feature, to remove or conceal the existence of unwanted light gradients, many times present in images captured with the low power objectives.

This function of an important utility, doesn't seem to be widely used by most microscopists. Let me therefore briefly present here its application in Motic (as well as Photoshop or Photopaint).
Incidentally the example that I present shouldn't be "normal". Such dust abundance would be only explained by a lot of laxity in the care of the microscope. In this case the dust was intentional.


 I often use this program because it is an integral part of the processing software of the DC-3 camera included in my microscope. A click on the appropriate icon opens the “amalgamation box”.

A click on First image, opens the directory tree, allowing the user to select the corresponding image. The "Second Image" button allows selection of the “correction screen”. The only method that allows the amalgamation is the “Proportionment” method. It is selected by default. By clicking "Amalgamation" the operation is performed. It may be that the first attempt is not entirely satisfactory and could be appropriate to reopen the correction screen and increase or decrease its contrast or “exposure”, before retrying. But generally no more than two attempts are required to get the desired result.

The final image is almost always something light in tone and low in contrast, but the Autocorrect Tools of any image editor, or simply the "gamma" correction can retrieve a good image.

02 - Aamalgamation result

    I detail the technique applicable with the Motic software so that anyone who wants to experiment with another image processor has an initial guide. 

Photoshop and PhotoPaint

    Both Photoshop and PhotoPaint have amalgamation software in their Images menu.     

    But offer many more options than the Motic, and the interested microscopist should try some (especially the “Superposition” commands, which in turn have options that offer various possibilities). In either program you should open simultaneously the already inverted “correction screen” image, and the image to correct.

    Then open the menu IMAGES, and select Calculations, or Calculate, which opens the job options.  Select first and second images in the dialog box, and apply Overlay. The degree of intensity of the overlay can be graduated, and this will depend on the photographed subject and the density of the “correction screen”. I got good results using 90 %.


RETURN TO THE ARTICLE on the Logitech Quickcam Pro 9000

Comments to the author, Walter  Dioni , are welcomed.

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Published in the February 2010 edition of Micscape.

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