reversed order for subtraction and division for math binary operation

[jilei-hao]

Dear Jilei,

I hope this message finds you well. I encountered a technical issue while attempting to post my message on the forum website (itksnap-users), and despite several attempts, I was unable to resolve the matter.

As per the guidelines and protocol, I understand the importance of communicating through the forum. However, due to the unforeseen circumstances, I am reaching out to you directly via email to ensure that my message does not go unnoticed.

Dear Jilei, I am writing to report an unexpected behavior I encountered while using the -divide command in c3d. According to the documentation, the -divide command should perform element-wise division of two images. However, when I attempted to divide Inphase.nii by opposite_phase.nii using the following command:

Inphase.nii opposite_phase.nii -divide -o ratio.nii

The resulting pixel values in ratio.nii were equal to the ratio of opposite_phase.nii to Inphase.nii, rather than the expected ratio of Inphase.nii to opposite_phase.nii. This unexpected behavior contradicts the documentation and makes it difficult to perform the desired arithmetic operation.

I have carefully reviewed the c3d manual guide to ensure that I am using the -divide command correctly. The documentation clearly states that the command should perform element-wise division of two images, yet the actual behavior is the opposite.

To reproduce this issue, please follow these steps:

1. Download two images, Inphase.nii and opposite_phase.nii.

2. Execute the following command:
   c3d Inphase.nii opposite_phase.nii -divide -o ratio.nii

3. Inspect the resulting image, ratio.nii, and verify that the pixel values are equal to the ratio of opposite_phase.nii to Inphase.nii.

I have included the images mentioned in this message for your consideration.

Best Regards, Mohammad

[jilei-hao]

c3d-divide-issue.zip