Firefly (or GH): Batch Bitmap Sample with Alpha – Recompose Image issue

I am new to Firefly and this my first test drive. I use Firefly because I need to image sample a batch of png files. The regular GH “Image Sampler” does not provide an input for path. Firefly does the job, except for one issue caused by a workaround:

I encounter a problem with reading RGB and Alpha values from png files.

Since “Bitmap Sampler” doesn’t return Alpha values, I went for a workaround:

  • “Decompose image”

  • “Recompose image” with Alpha mapped to R

  • “Bitmap Sampler”

  • “Split ARGB” (GH) to extract R (now representing the Alpha values)

This works fine until I try to feed a stack of several .png file through this algorithm using a grafted list of file paths.

While the RGB sampling works like a charm, the Alpha workaround delivers only identical values for different png files.

I think I have narrowed the issue down to the “Recompose image” component.

Are there known issues with “Recompose image” regarding paths / data structures?

I prepared a file to exemplify the issue: (27.5 KB)

Maybe I am missing the obvious or am just too tired… :slight_smile:

Any hints on:

  • how to avoid the workaround in the first place and
  • how to fix the problem that all my alpha values are the same
    would be highly appreciated.

Note: The original post was placed on

Thanks in advance!

Cheers, Frank

1 Like

All solved!

I learned the morning after that the Firefly image sampler has an option to sample alpha values (right click on component center). Everything works like charm, without workaround.

Sorry for wasting anyones time!

Cheers, Frank