3D Image Enhancement made EASY – Part III.

Comparing Simple Contrast Methods – cont'd.

Part I (April 25th.) of this series introduced a new method of image enhancement (simple '3D') and gave examples of its use.

Part II (May 3rd.) offered further examples of results using this method, particularly as compared to Brightfield and COL.

Part III continues this effort with examples at higher magnification and higher resolution.

Now, in casual microscopy, considerable time is often spent using the 40x ("high dry") objective. This lens offers the combined advantages of reasonably high magnification and resolution, decent working distance, and ease-of use. Also, almost every standard microscope has one. Further, more than 90% of what maybe seen (at high magnification) with Transmitted Light Microscopy may be seen using this type of lens. So, it seems only proper that we should determine just how well the 3D Mask method works with this lens…

In the first set, below, we compare results obtained using Brightfield with those using the Radial 3D mask method. This  set shows the same diatom photographed using each of these methods, with the results adjusted to approximate the actual visual appearance of the object. (If anything, these images understate the advantages of the 3D method, in part due to loss of image quality due to the use of the JPEG image format during image processing.)

Click anywhere on the above image for larger versions. 

Note that the measured width of diatom used in these photo is approximately 21 microns, which results in a calculated 'dot spacing' of about 1.0 microns. As this is reasonably within the resolution capability of the NA 0.70 objective, the performance of the objective itself should not be a limiting factor in these tests.

Not apparent in the photo set is the slight loss in overall image brightness associated with the 3D mask. However, this loss is a small penalty to pay for increased image contrast and resolution.

Radial 3D versus 'COL' – more surprises? 

In the second set, below, we compare the Radial 3D mask method with COL, a currently popular alternative method of contrast enhancement. Once again, the relative levels of image brightness are not preserved in these images, but here, COL typically suffers a much greater loss of overall brightness (typ. 3 to 4 times greater) than does the 3D mask method.

Click anywhere on the above image for larger versions. 

Here the 3D method appears to be at a disadvantage, at least initially, but only because the Condenser Iris was fully open (e.g: 100%).

However, as shown in the third photo set (below), this limitation is easily overcome by simply reducing the Iris opening.  This results in a sort of "variable contrast" mode, where the overall image contrast is readily controllable by means of the Condenser Iris. For Iris openings down to about 60%, there is very little loss in resolution, while even smaller openings (down to about 40-50%) may be used to achieve further increases in image contrast.

Click anywhere on the above image set for larger versions. 

Note that the COL method has no equivalent mode!

With COL results are fixed, as determined by the annulus diameter and opening width. To adjust contrast with COL either the entire Iris must be exchanged or a variable condenser, such as the scarce (and costly) Leitz 'Heine' Condenser, must be used. (Note that the Heine condenser will typically fit only a few older microscopes, whereas the Radial 3D mask method may be used on nearly any microscope equipped with a standard Condenser!)

Finally, remember that, with COL, usually the entire condenser annulus (or the Heine condenser setup) must be changed with every change of objective, while, with the Radial 3D mask method, only a simple Iris "tweak" is all that is typically be needed, if at all.

Next, in Part IV of this series, we will explore some of the unique possibilities for even greater image enhancement using the Radial 3D mask method…


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