Forum Technical Discussions      Re: Aggressive Radiographic Auditors Need to Take a Closer Look! Posted by: Ed Ginzel    (PID_67), E-mail: Address, on January 04, 2009 at 23:28 : In Reply to: Re: Aggressive Radiographic Auditors Need to Take a Closer Look! posted by : TJ , E-mail: Address, on January 04, 2009 at 21:53 : T.J. you seem to have missed the point about the perception effect. The Sprigner and Hermann grids are merely examples of the effect. Perhaps a closer related effect to our radiographic application is seen in the "Mach bands" (see a good description at http://neuro.bcm.edu/eagleman/papers/Eagleman.NatureRevNeuro.Illusions.pdf). It is not specifically the "grid" that I was referring to but instead the contrast effect that causes the brain to form a line where none exists (hence the concern that a radiographer MAY see a dark line and interpret it as a flaw where none exists). I have seen this effect on many radiographs as have hundreds of other radiographers. The trick is to know how to verify if it is real or illusion and this is NOT always simply proper vision, viewing conditions and a quality radiograph. If a good quality image in BMP format is available perhaps someone could upload a good image of the Mach bands...conversion to GIF tends to reduce the effect on screen ----------- Start Original Message ----------- : I'm not so sure about applying this phenomena completely to film interpretation. My reasoning is this grid is probably the furthest thing from the varying patterns of weld metal distribution you can demonstrate. : If you are inspecting bathroom tiles I could see a problem. In most cases, with the undercut (or lack of) is plain in interpretation. : TJ ------------ End Original Message ------------ Follow Ups: Re: Aggressive Radiographic Auditors Need to Take a Closer Look! TJ 12:29 Jan-05-2009 (5) Re: Aggressive Radiographic Auditors Need to Take a Closer Look! Nigel Armstrong 14:36 Jan-05-2009 (4) Re: Aggressive Radiographic Auditors Need to Take a Closer Look! chris s 18:06 Jan-06-2009 (0) Re: Aggressive Radiographic Auditors Need to Take a Closer Look! chris s 18:06 Jan-06-2009 (0) Re: Aggressive Radiographic Auditors Need to Take a Closer Look! Ed Ginzel 18:00 Jan-05-2009 (1) Re: Aggressive Radiographic Auditors Need to Take a Closer Look! Dent McIntyre 15:27 Jan-06-2009 (0) Post a Followup: Name: E-Mail: Subject: Comments: ----------- Start Original Message ----------- : T.J. you seem to have missed the point about the perception effect. The Sprigner and Hermann grids are merely examples of the effect. Perhaps a closer related effect to our radiographic application is seen in the "Mach bands" (see a good description at http://neuro.bcm.edu/eagleman/papers/Eagleman.NatureRevNeuro.Illusions.pdf). : It is not specifically the "grid" that I was referring to but instead the contrast effect that causes the brain to form a line where none exists (hence the concern that a radiographer MAY see a dark line and interpret it as a flaw where none exists). I have seen this effect on many radiographs as have hundreds of other radiographers. The trick is to know how to verify if it is real or illusion and this is NOT always simply proper vision, viewing conditions and a quality radiograph. : If a good quality image in BMP format is available perhaps someone could upload a good image of the Mach bands...conversion to GIF tends to reduce the effect on screen : : I'm not so sure about applying this phenomena completely to film interpretation. My reasoning is this grid is probably the furthest thing from the varying patterns of weld metal distribution you can demonstrate. : : If you are inspecting bathroom tiles I could see a problem. In most cases, with the undercut (or lack of) is plain in interpretation. : : TJ ------------ End Original Message ------------ Optional Link URL: Example: "http://www....html". Alternative write "http://www.ndt.net/wshop/attach/filename.htm" if you transfered a filename.htm via FTP Page Title: is important! Optional Image URL: http://www....gif Attention! Please click the button only once. This may take a moment to process Forum Technical Discussions Help