RAD 350 Chapt. 18 Viewing the Digital Image Human eye – Rods – scotopic/night vision – Cones – photopic/day vision Lumen is the basic photometric unit Luminous Flux – quantity of photometrix Illuminance – intensity of light on a surface

Light Terms con’t Luminance – brightness of a source of light (computer/tv screen) Inverse Square Law Cosine Law – If you view a screen/monitor from the side, the image is not as good as straight on

Hard vs soft copy Hard copy = radiograph on a viewbox Soft copy = image on a monitor/TV Cathode Ray Tube – digital viewing device Active matrix liquid crystal display (AMLCD) – MUCH BETTER viewing display than CRT Spatial resolution improves with HIGH megapixal display matrix

AMLCD con’t Measure of luminance of AMLCD = aperature ratio – AMLCD’s have less noise than CRT’s and better contrast resolution

Pre/post processing Pre-processing the image is automatic – but must have QC on the “system” at least annually Post processing required a PERSON to do – Annotation – labeling – Windows/level – playing with the grayscale (contrast) – Image flip – reorient the image – Image inversion – blacks to whites/whites to black

Pre/post con’t Subtraction (DSA) used to make things more visible (improve contrast) Pixel shift – “reregister an image” to correct for pt. motion Region of Interest (ROI) – determine a shade of contrast (gray) to display

PACS Picture archiving & communication system – Image acquisition system – Display system – Network – Storage system