Computation of reconstruction quality is flawed #4
Description
What steps will reproduce the problem?
1. Use RabbitCTRunner to test implementation
2. Observe computed root mean square error
What is the expected output? What do you see instead?
The RMSE of Thumper for the 512^3 volume is 0.0207 HU.
This result has been computed with 32-bit float values.
The required HU scaling has been applied.
(FACTOR = 1.2076081037521362, OFFSET = 24.0)
When the volumes are rounded to short integer precision,
which is the storage format of the reference volumes,
the RMSE increases dramatically to 0.115 HU.
However, RabbitCTRunner displays a value of 0.157 HU.
This deviation is caused by the use of a discontinuous
transfer function for the HU scaling in the following line:
float HU_ax = rec_volume[i] > 0.0f ? US_ROUND( (HUS[0] * rec_volume[i] +
HUS[1]) ) : 0.0f;
0.000f => 0.0f
0.001f => ~ 24.0f
This is also the reason why the maximum absolute error
is displayed as 24.0 HU by RabbitCTRunner.
The real maximum absolute error of Thumper is 0.662 HU.
What version of the product are you using? On what operating system?
The latest version of RabbitCTRunner.
The operating system is not relevant to this issue.
Please provide any additional information below.
The discontinuous transfer function can be fixed easily.
However, the computed RMSE is affected dramatically by
storing the reference volumes in short integer format.
Original issue reported on code.google.com by zinsser...@gmail.com on 8 Jan 2013 at 10:27