GenICamBrowser

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Note that all the quantities in this equation have to be expressed in centimeters. Often, we want the image to be at the near-point distance (L=25cmL=25cm) to get maximum magnification, and we hold the magnifying lens close to the eye (ℓ=0ℓ=0). In this case, Equation 2.29 gives

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GenICamsoftware

The apparent size of an object perceived by the eye depends on the angle the object subtends from the eye. As shown in Figure 2.36, the object at A subtends a larger angle from the eye than when it is position at point B. Thus, the object at A forms a larger image on the retina (see OA′OA′) than when it is positioned at B (see OB′OB′). Thus, objects that subtend large angles from the eye appear larger because they form larger images on the retina.

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GenICamC++

We have seen that, when an object is placed within a focal length of a convex lens, its image is virtual, upright, and larger than the object (see part (b) of Figure 2.26). Thus, when such an image produced by a convex lens serves as the object for the eye, as shown in Figure 2.37, the image on the retina is enlarged, because the image produced by the lens subtends a larger angle in the eye than does the object. A convex lens used for this purpose is called a magnifying glass or a simple magnifier.

Once you loaded a device description file on a node map object, you would start to control GenICam feature nodes to control the target device. Now assume that we are going to control a GenICam feature node called Foo. To get the value of Foo, we code as follows:

To account for the magnification of a magnifying lens, we compare the angle subtended by the image (created by the lens) with the angle subtended by the object (viewed with no lens), as shown in Figure 2.37. We assume that the object is situated at the near point of the eye, because this is the object distance at which the unaided eye can form the largest image on the retina. We will compare the magnified images created by a lens with this maximum image size for the unaided eye. The magnification of an image when observed by the eye is the angular magnification M, which is defined by the ratio of the angle θimageθimage subtended by the image to the angle θobjectθobject subtended by the object:

Genicamapp

which shows that the greatest magnification occurs for the lens with the shortest focal length. In addition, when the image is at the near-point distance and the lens is held close to the eye (ℓ=0)(ℓ=0), then L=di=25cmL=di=25cm and Equation 2.27 becomes

By comparing Equation 2.29 with Equation 2.32, we see that the range of angular magnification of a given converging lens is

Consider the situation shown in Figure 2.37. The magnifying lens is held a distance ℓℓ from the eye, and the image produced by the magnifier forms a distance L from the eye. We want to calculate the angular magnification for any arbitrary L and ℓℓ. In the small-angle approximation, the angular size θimageθimage of the image is hi/Lhi/L. The angular size θobjectθobject of the object at the near point is θobject=ho/25cmθobject=ho/25cm. The angular magnification is then

where m is the linear magnification (Equation 2.32) derived for spherical mirrors and thin lenses. Another useful situation is when the image is at infinity (L=∞)(L=∞). Equation 2.29 then takes the form

GenICamdownload

GenICamPython

There is a sister project of the GenICam Python binding. It’s called Harvester and is a reference implementation of the GenICam Python binding. Harvester gives you an intuitive way for image acquisition to make your life easier.

The resulting magnification is simply the ratio of the near-point distance to the focal length of the magnifying lens, so a lens with a shorter focal length gives a stronger magnification. Although this magnification is smaller by 1 than the magnification obtained with the image at the near point, it provides for the most comfortable viewing conditions, because the eye is relaxed when viewing a distant object.

In the EMVA website, you can get useful resources to learn and use GenICam standards and its compliant devices and software:

Harvester is distributed under the Apache version 2 license so you can use it for free; however, note that GenICam applies for another license. The source code can be found at GitHub.

And then, load a device description file on the node map object. The NodeMap object supports several ways to make it. One is to load the file content as a str object:

From part (b) of the figure, we see that the absolute value of the image distance is |di|=L−ℓ|di|=L−ℓ. Note that di<0di<0 because the image is virtual, so we can dispense with the absolute value by explicitly inserting the minus sign: −di=L−ℓ−di=L−ℓ. Inserting this into Equation 2.28 gives us the final equation for the angular magnification of a magnifying lens:

The genicam module consists of two sub-modules. The one is genapi and the other is gentl. The genapi module gives you a way to control GenICam features of the target device supports. On the other hand, the gentl module gives you a way to control functionality that the target GenTL Producer supports.