Business

 

Introduction to Modulation Transfer Function | Soukacatv.com


HDMI Encoder Modulator,16in1 Digital Headend,HD RF Modulator at SOUKA

07.01.2019 11:37:48 - When optical designers attempt to compare the performance of optical systems, a commonly used measure is the modulation transfer function (MTF). MTF is used for components as simple as a spherical singlet lens to those as complex as a multi-element telecentric imaging lens assembly.

(live-PR.com) - When optical designers attempt to compare the performance of optical systems, a commonly used measure is the modulation transfer function (MTF). MTF is used for components as simple as a spherical singlet lens to those as complex as a multi-element telecentric imaging lens assembly. In order to understand the significance of MTF, consider some general principles and practical examples for

 

defining MTF including its components, importance, and characterization.
HDMI Encoder Modulator,16in1 Digital Headend,HD RF Modulator at SOUKA www.soukacatv.com/.
THE COMPONENTS OF MTF
To properly define the modulation transfer function, it is necessary to first define two terms required to truly characterize image performance: resolution and contrast.
Resolution
Resolution is an imaging system's ability to distinguish object detail. It is often expressed in terms of line-pairs per millimeter (where a line-pair is a sequence of one black line and one white line). This measure of line-pairs per millimeter (lp/mm) is also known as frequency. The inverse of the frequency yields the spacing in millimeters between two resolved lines. Bar targets with a series of equally spaced, alternating white and black bars (i.e. a 1951 USAF target or a Ronchi ruling) are ideal for testing system performance. For a more detailed explanation of test targets, view Choosing the Correct Test Target. For all imaging optics, when imaging such a pattern, perfect line edges become blurred to a degree (Figure 1). High-resolution images are those which exhibit a large amount of detail as a result of minimal blurring. Conversely, low-resolution images lack fine detail.

Figure 1: Perfect Line Edges Before (Left) and After (Right) Passing through a Low Resolution Imaging Lens
A practical way of understanding line-pairs is to think of them as pixels on a camera sensor, where a single line-pair corresponds to two pixels (Figure 2). Two camera sensor pixels are needed for each line-pair of resolution: one pixel is dedicated to the red line and the other to the blank space between pixels. Using the aforementioned metaphor, image resolution of the camera can now be specified as equal to twice its pixel size.

Figure 2: Imaging Scenarios Where (a) the Line-Pair is NOT Resolved and (b) the Line-Pair is Resolved
Correspondingly, object resolution is calculated using the camera resolution and the primary magnification (PMAG) of the imaging lens (Equations 1 – 2). It is important to note that these equations assume the imaging lens contributes no resolution loss.
(1)
(2)
Contrast/Modulation
Consider normalizing the intensity of a bar target by assigning a maximum value to the white bars and zero value to the black bars. Plotting these values results in a square wave, from which the notion of contrast can be more easily seen (Figure 3). Mathematically, contrast is calculated with Equation 3:
(3)

Figure 3: Contrast Expressed as a Square Wave
When this same principle is applied to the imaging example in Figure 1, the intensity pattern before and after imaging can be seen (Figure 4). Contrast or modulation can then be defined as how faithfully the minimum and maximum intensity values are transferred from object plane to image plane.
To understand the relation between contrast and image quality, consider an imaging lens with the same resolution as the one in Figure 1 and Figure 4, but used to image an object with a greater line-pair frequency. Figure 5 illustrates that as the spatial frequency of the lines increases, the contrast of the image decreases. This effect is always present when working with imaging lenses of the same resolution. For the image to appear defined, black must be truly black and white truly white, with a minimal amount of grayscale between.

Figure 4: Contrast of a Bar Target and Its Image

Figure 5: Contrast Comparison at Object and Image Planes
In imaging applications, the imaging lens, camera sensor, and illumination play key roles in determining the resulting image contrast. The lens contrast is typically defined in terms of the percentage of the object contrast that is reproduced. The sensor's ability to reproduce contrast is usually specified in terms of decibels (dB) in analog cameras and bits in digital cameras.
Established in 2000, the Soukacatv.com (DSW) main products are modulators both in digital and analog modulators, amplifier and combiner. We are the leading communication supplier in manufacturing the headend system in China. Our 16 in 1 and 24 in 1 now are the most popular products all over the world. For more, please access to www.soukacatv.com/.

Source: www.edmundoptics.com/resources/application-notes ..


Press Information:
Dingshengwei Electronics Co., Ltd

Buliding A,the first industry park of Guanlong,Xili Town,Nanshan,Shenzhen,Guangdong,China

Contact Person:


Phone: +86 13410066011
eMail: eMail

Web: http://https://www.soukacatv.com/



 

Disclaimer: If you have any questions regarding information in this article please contact the author. Please do not contact Live-PR.com. We are not able to assist you. Live-PR.com disclaims content contained in this article. Live-PR.com is not authorized to give any information about content and not responsible for content posted by third party.
refer this article
Print This Article
Terms Of Use Privacy About Live-PR.com Contact Us