7.5.2 The minimum contrast as deter

7.5.2 The minimum contrast as determined by the ratio of the screen brightness at the maximum DDL compared to the screen brightness at the minimum DDL shall be 250:1. 7.5.3 The image display shall be capable of displaying linear patterns of alternating pixels at full contrast in both the horizontal and vertical directions without aliasing. 7.5.4 The display shall be free of discernable geometric distortion. 7.5.5 The display shall be free of screen flicker, characterized by high frequency fluctuation of high contrast image details. 7.5.6 The image display shall be capable of displaying a 5 % DDL block against a 0 % DDL background and simultaneously displaying a 95 % DDL block against a 100 % background in a manner clearly perceptible to the user. An image display test pattern, in accordance with the requirements of SMPTE RP 133, shall be configured for the system display resolution and aspect ratio.Alternate test patterns may be used provided they include the features described in SMPTE RP133 required to perform the quality tests specified in this practice. 7.5.7 The monitor shall be capable of discriminating the horizontal and vertical low contrast (1 %) modulation patterns at the display center and each of the four corner locations. 7.6 Image Quality Indicators (IQI): 7.6.1 IQIs shall be in accordance with a recognized standard or approved by the Cognizant Engineering Organization. Hole plate type indicators shall comply with Practice E1025 or Practice E1742, Annex 1. Wire type indicators shall be in accordance with Practice E747 and correlated to the hole type penetrameters in accordance with Practice E747. 7.6.2 The IQI shall be constructed from material in the same material group (see Practice E1025) as the material to be radiologically inspected. If an IQI material of the same material group is not available, a material that is radiologically less dense shall be used. 7.6.3 The use of alternative IQIs that are approved by the CEO shall be documented in a written procedure with the design, materials designation, and thickness identification or documented on a drawing and that drawing referenced in the procedure. 7.6.4 The IQIs shall be procured or fabricated to the requirements of Practice E1025 or Practice E747 with a manufacturer’scertificationofcompliancewithrespecttoalloy and dimensions. Users shall visually inspect IQIs for damage and cleanliness in accordance with Appendix X1. 7.7 Radiation Sources: 7.7.1 X-Radiation Sources—Selection of appropriate X-ray voltage and current levels is dependent upon variables regarding the specimen being examined (material type and thickness) and exposure time. The suitability of these exposure parameters shall be demonstrated by attainment of the required radiographic quality level and compliance with all other requirements stipulated herein. 7.7.2 Gamma Radiation Sources—Isotope sources that are used shall be capable of demonstrating the required radiographic quality level