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PostPosted: 28.10.2019, 19:56 
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Joined: 19.10.2019, 16:47
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The following table for image quality could be found in the guide for film E94 (Fig. 1 page 5)):

It can be used also for DDA technique:

with CNR (Contrast to Noise Ratio) and SNR (Signal to Noise Ratio). Sometimes Contrast Sensitivity is used, it is 1/CNR.

The unsharpness and contrast is very similar. The biggest difference is the "noise"; with buying the film the noise level is defined with the film class (capacity for dose and film granularity). With DDAs the matrix of the pixel is always in the same position that several images can be captured and accumulated in a computer to overcome the "single shot" dose limit of film (or CR).
The following diagram should show this difference. To compare film and DDAs the film is digitized and the SNR is normalized to a 100µm round aperture (sqared shaped area of 88.6µm x 88.6µm) to have the same SRB.

The measurement was done at BAM in Berlin with different energies and different accumulation times - up to 25 minutes - to get a very high SNRnorm which could be factor 40 better than the best film.


Last edited by Klaus on 28.10.2019, 21:27, edited 1 time in total.

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PostPosted: 28.10.2019, 21:25 
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To demonstrate the influence of noise on detail visibility here is a picture of the Ypsilon Mountain:
SNR = 5

SNR = 80

This is very similar with X-Ray images; here is an example with the BAM 5 weld (see picture in header between Fand f).
1. Film AGFA D2, class C1 EN 584-1, 330s exposure time; no magnification (SNRnorm = 130)

2. PerkinElmer XRD1620 detector (200µm SRB), 100s exposure time; magnification of 3.0 (SNRnorm = 520 - limited by the surface structure of the material beside the weld)

highpass filter with same parameters applied on both images


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