The "latest" (old) beta for
SCI Companion has support for converting bitmap images to pic resources.
Steps:
1) create new pic (button on left of toolbar)
2) choose Tools->Convert bitmap to Pic
3) It brings up a dialog when you can browse for an image, or copy from the clipboard. The image should appear on the left side
4) Click "convert", and the resulting SCI pic should appear on the right. If it looks ok, then click "accept", and the appropriate drawing commands will be inserted into your pic.
5) choose file->export as resource to save it as a pic.nnn file that can be imported by SCI Studio.
But a big WARNING: large pics can wreak havoc on your game due to memory constraints. And while my program does a better job than pcx2pic (if you can even get that to work), the resultant pic sizes are still large. The max size of a resource is 64KB, but I wouldn't get too close to that. SCI Companion shows how big the result is, so you can check before clicking "accept". You can adjust the palette used, and the number of colours and "convert" again, to try to get something that may not look quite as good, but will be smaller. I can usually get something decent of about 40KB... although of course it depends on what the original picture looks like.