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简单介绍:
在中性区域内放置四个密度为D~0.4的大型环形波带片。每个环形波带片由宽度和距离向外递减的同心圆组成。由于圆形环的几何形状使得带片的空间频率随着与圆心距离的增加而线性增加。外缘的圆形环有575行/图片高度,因此空间频率为575/2=287.5周或线对每幅高度。在我们625行电视系统(575个有效行,52μs有效行时长,长宽比4:3)中相当于水平方向上7.4MHz的空间频率。根据625线电视系统电子光束扫描定理水平线287.5周每幅高度可以只或只是没有得到解决(奈奎斯特频率)。 环形波带片测试图串色干扰测试卡T63P分辨率测试图卡爱莎测试卡 环形波带片测试图串色干扰测试卡T63P分辨率测试图卡爱莎测试卡 环形波带片测试图串色干扰测试卡T63P分辨率测试图卡爱莎测试卡
详情介绍:

 

 

检测TV摄像和传输系统的分辨率特性以及串色干扰。

数据

在中性区域内放置四个密度为D~0.4的大型环形波带片。每个环形波带片由宽度和距离向外递减的同心圆组成。由于圆形环的几何形状使得带片的空间频率随着与圆心距离的增加而线性增加。外缘的圆形环有575行/图片高度,因此空间频率为575/2=287.5周或线对每幅高度。在我们625行电视系统(575个有效行,52μs有效行时长,长宽比4:3)中相当于水平方向上7.4MHz的空间频率。根据625线电视系统电子光束扫描定理水平线287.5周每幅高度可以只或只是没有得到解决(奈奎斯特频率)。

在图片中心有一个小环形波带片空间频率高达大环形波带片的两倍。这个中心圆形区域的外边缘空间频率每幅高度1150/2=575周或线对。这就相当于水平方向频率为14.8MHz。

图片左边和右边分辨显示一个白色和一个黑色竖线密度分别为D~0.1和D1.7。这两个条用来作为示波器测量分辨率以及水平调整的参考值。

应用

环形波带片测量法被证明非常有价值尤其是对电视屏幕主观比较测量。但不适合客观测量。因此它不是一个在服务测试方法。环形波带片测量法是为开发新的系统和设备起重要辅助作用。它也可以被推荐用于在核准测量结果。

测试卡特点

 

使用环形波带片测量法辅助下可以确定TV摄像机以下几个特征:

•水平、垂直和对角方向的分辨率

•分辨率和扫描光点之间的相关性

•水平和垂直光圈校正效果

•相机扫描光束的散光(管摄像机)

•所述环形波带片和电视行相应彩色显像管的荫罩结构之间的干涉的影响

•PAL编码的效果(如串色)

•相机的水平和垂直运动(或者在测试)中反应

•动态清晰度

•颞干扰(例如串色)

环形波带片的使用方法尤其适合测试电视信号过滤multidimensonally(水平、垂直和暂时的)对象。这些可以是TV摄像机或标准的PAL***(带线延迟)和组合式过滤PAL***光圈校正。环形波带片也可以测量MAC系统(具有线序色彩传输)过滤前后的效果。这种光环形波带片测试卡用于检测CCD摄像机非常有用。

测试卡说明

当使用这张测试分辨率时被测试设备必须指出与光学带片测试图在圆形领域密度的急剧变化。这意味着,除了空间频率的基波也存在谐波。当使用电视线系统扫描该环形波带片的谐波超过奈奎斯特频率可能会导致电视图像干涉模式(所谓的混叠成分),其再次显示带片。这种环形波带片干扰结果是由于环形波带片测试图与扫描电视线系统之间的干扰引起的。隔行扫描干扰环形波带片区域并不是静态的,而是以25Hz的频率节奏闪烁的。

当使用相机电子光学扫描(管摄像机)工作这些干扰通常非常低,因为在扫描电子束由于其三维扩展具有不同的低通滤波器特性。这导致了图像拍摄的预滤波。这使得图像要拍摄一个预先滤波。与CCD摄像机的反应是不同的。由于在水平方向和垂直方向上显着的干涉图案的CCD元件,在水平方向和垂直方向可能会出现的明确界定的几何结构(见图)。

在PAL传输期间附加串色干扰通过色链低密度组分的相互调制。过程中颜色的PAL编码带片测试卡再现监视串色干扰可以被看作是具有小脉动彩色环形波带片其中心在PAL制式彩色副载波频率4.43MHz的位于水平方向。在PAL***梳理工作中过滤串色干扰一般动态图像(即当摄像机或测试图被移动)比静止图片更重要。

事实上,PAL编码器,尤其是PAL***是串色干扰主要原因,即使是过于“锋利”光圈校正都可能大大增加串色。为了确定串色干扰的原因,建议不仅使用光带片测试卡(以及摄像机),还要使用电子环形波带发生器。

一般而言,建议使用环形波带片发生器每当测试对象具有电输入。除了像光圈校正,PAL编码器和***还监控传输设备。相比于光环形波带片测试卡有一个优点,那就是环形波带片的输出信号可以是生成在一个正方形或连续正弦转换。动力学环形波带片也可以轻松地以电子方式实现。

 

Checking resolution characteristics and cross color interferences of TV cameras and TV transmission systems

DATA

On a neutral surrounding area with a density of D ~ 0.4 four large zone plates are arranged. Each zone plate consists of concentric circular rings, with their width and distances decreasing outwards. The geometry of the circular rings causes the space frequencies of the zone plate to increase linearly with the distance from the circle center. At the outer edge of the circular rings we have 575 lines per picture height and thus a spatial frequency of 575/2 = 287.5 periods or line pairs per picture height. In our 625 line TV system (575 active lines, 52 μs active line duration, aspect ratio 4:3) this corresponds to a frequency of 7.4 MHz in horizontal direction. According to the scanning theorem horizontal lines of 287.5 periods per picture height can just or just not be resolved (Nyquist frequency) by a 625 line TV system.

In the picture center there is a small zone plate with the spatial frequencies being twice as high as those of the large zone plates. At the outer edge of this central circular field we have a spatial frequency of 1150/2=575 periods or line pairs per picture height. This corresponds to a frequency of 14.8 MHz in horizontal direction.

The left and right edges of the picture show one white and one black vertical bar each with densities of D~0.1 resp. D~1.7. These bars serve as a reference when measuring the resolution by oscilloscope as well as for level adjustment.

UTILISATION

The Zone Plate method has proved worthwhile especially for subjective comparison measurement at the TV screen. For objective measurement it is less suitable. Therefore it is not an in service test method. The Zone Plate method is rather an important aid for developing new systems and devices. And it also can be recommended for comparison during approval measurements.

With the aid of the Zone Plate method the following characteristics of TV cameras can be determined:

• resolution in horizontal, vertical and diagonal direction

• correlation between the resolution and the scanning spot

• effects of horizontal and vertical aperture corrections

• astigmatism of the camera scanning beam (tube cameras)

• effects of interferences between the zone plates and the television line resp. the shadow mask structure of color picture tubes

• effects of PAL coding (e.g. cross color)

• reaction during horizontal and vertical movement of the camera (or the test chart)

• dynamic resolution

• temporal interferences (e.g. due to cross color)

The use of the Zone Plate method is particularly recommended for test objects where the television signal is filtered multidimensonally (horizontally, vertically and temporally). These can be aperture correctors of TV cameras or standard PAL-decoders (with line delays) and combifilter PAL-decoders. Zone Plates also allow to determine the effects of pre- and post-filtering of MAC-systems (with line-sequential color transmission). Particularly useful is the optical Zone Plate Test Chart for checking CCD cameras.

When measuring resolution it has to be noted that with the optical Zone Plate Test Chart the density in the circular fields changes rapidly. This means that besides the fundamental wave of the space frequencies there are also harmonic waves. When scanning the zone plates with the TV line system those harmonic waves which surpass the Nyquist frequency may cause interference patterns in the television picture (the so-called aliasing components) which again show zone plates. These interference zone plates result from interference between the Zone Plates of the test chart and the scanning television line system. Due to the interlaced scanning the interference zone plates are not static but flicker in a 25 Hz rhythm.

When working with cameras with electron-optical scanning (tube cameras) these interferences are usually very low since the scanning electron beam has a distinct low-pass filter characteristic due to its three-dimensional extension. This leads to a pre-filtering of picture shot. The reaction with CCD cameras is different. Due to the clearly defined geometric structure of the CCD elements in horizontal and vertical direction noticeable interference patterns both horizontally and vertically may occur (see picture).

During PAL-transmission ther are in addition cross-color interferences through cross-talking of light density components in the chromatic chain. During reproduction of a PAL-coded Zone Plate Test Chart on a color monitor the cross-color interferences can be seen as small pulsating colored zone plates with their centers lying in horizontal direction at the PAL color sub-carrier frequency 4.43 MHz. When the PAL decoder works with comb filters the cross-color interferences are generally less significant in stationary pictures than in moving pictures (i.e. when camera or test chart is moved).

In fact the PAL coder and especially the PAL decoder are primarily responsible for the cross color interferences, but even a too “sharp” aperture correction may increase the cross color considerably. In order to locate the cause of cross color interferences it is recommended to work not only with the optical Zone Plate Test Chart (and the camera) but also with an electronic zone plate generator.

In general it is recommended to use a zone plate generator whenever test object has electric inputs. These are besides transmission devices like a aperture correctors, PAL coders and decoders also monitors. Compared to the optical Zone Plate Test Chart zone plate generators have the advantage that the output signals of the zone plate can either be generated in a square shape or as continuous sinusoidal transitions. Dynamising the Zone Plate can also be effected easily in an electronic way.

 

产品购买须知
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  • 2、关于尺码

     机身和包装尺寸为手动测量,由于测量工具和测量方法不同的因素,会存在1cm误差,但是不用影响运输和使用。

  • 3、关于颜色

     小店产品都是实拍图片,但是由于不同显示器分辨率以及色温和对比度差异有所不同。 

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测试卡注意事项

反射测试卡应该以45°角斜置,防止标准光泽效果产生的影响。为了防止和推迟紫外线照射引起的褪色现象,测试卡不使用是应该盖上测试卡覆盖。

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