Like Ofnuts and rich2005, not sure what you are asking, maybe be go straight to the point, something like "I want from this before > to this after"
Anyway let's start for what I understood
Duplicate your image twice
Check that your color background is white >
, then on the top layer in the layers' dialog, right click on it, a context menu opens > Remove Alpha Channel (or you can go to Layer > Transparency > Remove Alpha Channel )
Then select the layer in the middle (still in the layer's dialog), then go to Filters > Generic > GEGL graph... and input these value > gegl:opacity value=5.55 < (copy/paste)
Re-activate the top layer and put it in Screen Mode then play with the opacity slider to have more light(white) or less light,
the lab-gown is fully opaque while retaining a transparent background all around
Note: you could do the middle layer with, Layer > Transparency > Threshold alpha..., but this filter will "pixelize" between transparency and opaque, thus it's better to use GEGL graph IMO
Anyway let's start for what I understood
Duplicate your image twice
Check that your color background is white >
, then on the top layer in the layers' dialog, right click on it, a context menu opens > Remove Alpha Channel (or you can go to Layer > Transparency > Remove Alpha Channel )Then select the layer in the middle (still in the layer's dialog), then go to Filters > Generic > GEGL graph... and input these value > gegl:opacity value=5.55 < (copy/paste)
Re-activate the top layer and put it in Screen Mode then play with the opacity slider to have more light(white) or less light,
the lab-gown is fully opaque while retaining a transparent background all around
Note: you could do the middle layer with, Layer > Transparency > Threshold alpha..., but this filter will "pixelize" between transparency and opaque, thus it's better to use GEGL graph IMO