I am trying to link the Read node format of my input images to a Constant node down the tree as I am trying to process a bunch of images with varying resolutions and aspect ratios.
I tried Ctrl dragging the format from the Read node to the Constant node to have it update if that is even a thing I can do.
I am fairly new to Nuke if you can't already tell.
It's quite easy to do what you need: Just create two nodes – Read1 (with some content) and Constant1 and execute the following code in NUKE's script Editor:
import nuke
sourceWidth = nuke.toNode("Read1").width()
sourceHeight = nuke.toNode("Read1").height()
nuke.tcl('add_format "%s %s temporaryResolution"' % (sourceWidth, sourceHeight))
nuke.toNode("Constant1").setSelected(True)
nuke.createNode("Reformat")['format'].setValue('temporaryResolution')
Aa a result you'll get a Reformat node connected to Constant1 with new width and height values.
You can avoid this problem entirely by just not using the Constant node, and instead make a blank image from your source imagery - that way it automatically inherits the input format.
Put differently, say you have something like so:
The constant has no input, therefore it has to specify a format - but all it does is make an empty image. What we want is a blank image but with the same format as the source image, so instead we can start with the source image, and simply remove all the channels (Remove node set to "channels: all"), then a Shuffle to recreate the default rgba layer. Something like so:
This way no scripting is required, so the problems of when the format-linking expressions are evaluated is avoided