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Federal Agencies Digitization Initiative Still Image Working Group — August 2010 Part II - Evaluation and Quality Control of Digital Imaging - SIGNAL - OECF — Opto Electronic Conversion Function ( ISO 14545) TTF — Tone Transfer Function TRC — Tone Reproduction Curve definition : Average large area digital response of an electronic imaging device to light stimuli 2 LB GB i Sensitivity (ISO 12232) Gefinition: The reciprocal of the amount of light necessary to Derivative Metrics ne and S definition : characteristic behavior of large area digital output response ( count value) to spectrally neutral White Balance/Neutrali definition : equivalence of large area color channel! output responses to a range of spectrally neutral input stimuli Color Encoding/Rendering cefinition: The difference between selected physically measured input colors and their achieve a desired output input stimuli ( gray patch) intended output rendering from a given color response. space. ~ Responsivity = Too dark/light - Color cast ~ Over/under saturated colors Y = Speed - Under/over exposed « Gray balance = Color balance is wrong =| ~ Exposure Index (EI) ~ No shadow/highlight detail - Memory colors are not correct 5 - Clipping — Color Accuracy = Contrast — Color Saturation iw ~ Exposure Accuracy >E @: Saturation based speed @: Average, median, maximum or @: Average, median, maximum, or RMS Qs RMS deviation from aim for neutral deviation from aim for chromatic patches of § units: TBD patches of interest. @: Average, median, maximum, or interest os units: Count Values, AL*, Density, F- RMS deviation from aim between color ; D : stops channels ( R-G, R-B, G-B ) for neutral Units (@): Count Values, Delta E (AE), Delta 5 2 | ~: Noise based speed : Deviation from a reference OECF | Patches of interest. E (AE,*ps), c units: TBD mma value s _ ga u Units (®): Count Values, AEssps, Units (7): Delta C, Delta H =F O: Exposure Index, Standard | units: gamma ( unitless) Units (‘@): Delta C, Delta H Ss 2 Output Sensitivity - Inefficient imaging detector Possible failure Causes ~—Auto-contrast failures -Inappropriate black/white point calibration. - Wrong gamma selection or tone aim — Poor auto-white balance algorithm - Bad white /black point calibration — Sparse gray patch balancing — Color Balance — Strongly colored environmental surround ~ Color profile tweaked for preference ~ Wrong color profile intent ~- Wrong color profile chosen/embedded - Color profile assumptions inconsistent with practice (i.e. lighting quality, gamma, intent, etc.) - Environmental : highly chromatic color surround/dothing Technical Guidelines for Digitizing Cultural Heritage Materials: Creation of Raster Image Master Files