Fix(2d_segmentation): Restore the predicted value of seg image to the range of 0~225 before saving it (#1951)

### Description
To fix the problem that evaluation output images are all black because
`post_trans` scale their pixel values to 0~1.

### Checks
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applicable items -->
- [ ] Avoid including large-size files in the PR.
- [ ] Clean up long text outputs from code cells in the notebook.
- [ ] For security purposes, please check the contents and remove any
sensitive info such as user names and private key.
- [ ] Ensure (1) hyperlinks and markdown anchors are working (2) use
relative paths for tutorial repo files (3) put figure and graphs in the
`./figure` folder
- [ ] Notebook runs automatically `./runner.sh -t <path to .ipynb file>`

Signed-off-by: Rekawiia Lin <Linhk1606@outlook.com>
Co-authored-by: YunLiu <55491388+KumoLiu@users.noreply.github.com>