Fail with an error for some images

For instance:

```
root@167545c2c5e4:/approx-vision/pipelines/common# ./pipeline_V2.o /datasets/000000431848.png /datasets/
Error at ./pipeline_V2.cpp:153:
Input buffer b0 is accessed at 2, which is beyond the max (-1) in dimension 2
Aborted (core dumped)
```

There should be check for number of channels while conversion to RAW format. Raise en error if gray-scale image is passed

Reproduce the failure with ./pipeline_V2.o using the grayscale image command from the issue, then inspect pipeline_V2.cpp around line 153 and the conversion to RAW format. Confirm the expected behavior for images with different channel counts; done means grayscale input produces a clear error instead of aborting with the buffer-access failure.

Written by the indexing model from the issue text.