The scanner used at ISMD was a HOWTEK MultiRAD 850. Cases with a filename beginning with the letter 'D' came from ISMD. Cases from ISMD that have HOWTEK in the .ics file were scanned on the HOWTEK scanner at ISMD and can be calibrated to optical density with the equations in this file.
A step-wedge phantom film was scanned on the HOWTEK scanner at the full 43.5 micron per pixel spatial resolution. The optical density of each step was measured several times, and the average values were calculated. The step-wedge was scanned and the average gray level was computed for each patch of uniform optical density. The results are listed below:
Measured Grey Level Mean Three Raw Optical
Optical Density (Standard Deviation) Density Measurements
--------------- -------------------- ----------------
3.09333333333 934.607 44.538 3.14 3.10 3.04
3.04333333333 982.670 51.491 3.07 3.03 3.03
2.80333333333 1244.729 114.356 2.83 2.80 2.78
2.56000000000 1451.243 83.226 2.58 2.56 2.54
2.36333333333 1609.725 65.231 2.39 2.36 2.34
2.20666666667 1748.061 57.129 2.23 2.20 2.19
2.08000000000 1880.708 50.344 2.10 2.08 2.06
1.96666666667 1995.271 40.674 1.98 1.97 1.95
1.86333333333 2098.371 37.892 1.88 1.86 1.85
1.77666666667 2190.713 35.160 1.79 1.78 1.76
1.68666666667 2277.971 30.763 1.70 1.69 1.67
1.60333333333 2359.617 29.154 1.62 1.60 1.59
1.51666666667 2441.160 29.536 1.54 1.52 1.49
1.43666666667 2518.183 28.332 1.45 1.44 1.42
1.35333333333 2603.009 33.506 1.37 1.36 1.33
1.28000000000 2686.381 34.039 1.30 1.29 1.25
1.21000000000 2762.442 30.239 1.22 1.22 1.19
1.13666666667 2836.072 26.488 1.15 1.14 1.12
1.07000000000 2900.947 24.478 1.09 1.07 1.05
1.00333333333 2971.209 25.553 1.02 1.01 0.98
0.93666666667 3041.031 26.363 0.95 0.94 0.92
0.86666666667 3112.714 26.504 0.88 0.87 0.85
0.81333333333 3183.863 25.264 0.83 0.81 0.80
0.75000000000 3251.031 22.654 0.76 0.75 0.74
0.69000000000 3317.778 19.332 0.70 0.69 0.68
0.62000000000 3382.764 17.910 0.63 0.62 0.61
0.56000000000 3445.922 18.527 0.57 0.56 0.55
0.51000000000 3507.946 18.177 0.52 0.51 0.50
0.43333333333 3576.333 17.974 0.40 0.46 0.44
0.33333333333 3650.796 15.667 0.34 0.34 0.32
0.28000000000 3777.119 9.564 0.28 0.28 0.28
0.22333333333 3836.090 6.828 0.23 0.22 0.22
0.17333333333 3885.350 4.934 0.16 0.18 0.18
A linear regression was done to predict optical density grom gray value. It produced the following equation that can be used to estimate the optical density for pixel values in images digitized on this scanner.
ISMD_HOWTEK_optical_density = 3.96604095240593 + (-0.00099055807612) * (pixel_value)