Saving and exporting alpha channels

[drferry]

Apparently it is not possible in Photoshop to save an alpha channel as an external document and load that channel into another Photoshop file for use there. This seems to me to be a most egregious defficiency.  This problem arose when I took a sequence of 900 photos and wanted to run an action on all of them to adjust exposure and do color correction before importing them into Adobe Premiere Pro.  The sky needed different adjustment than the foreground, so I made a complex selection of the sky and saved it as an alpha channel, planning to use it as part of an action in the Image Processor for all of the shots.  However, according to a chat with Adobe Help, no can do.

I did think of a work around, however, which is to open the alpha channel, selct it, copy it, and paste it into a new layer in the Layers panel.  Then Export Layers to Files, load the saved layer into a new Photoshop file, and copy and paste it into a new channel in the Channels panel.  I could then perform all of my adjustments and merge the layers.  I could build an action to do all of this and run the Image Processor on all 900 files.

Please let me know if I am on the right track or if anyone has a better idea.

[davescm]

Hi

You could use Image > Calculations to make a new Alpha channel (or a selection) in the second document using  the Alpha in the first as teh source. Use Blending mode normal in calculations so it only uses the one channel.

This is recordable as an action so you could record this calculations operation as part of an action to make the adjustment , then run image processor using that action - making sure you kept the first document (with the original alpha) open throughout.

Dave

[Conrad C]

Another way to completely avoid copying and pasting is to use two commands that are not obvious because they are not in the Channels panel: Select > Load Selection and Select > Save Selection. When you use these commands, you can load a selection from or save it to an alpha channel in the same document or another open document. Unfortunately you can’t load an alpha channel from a document that is not open, but you can leave it open while running the action on a folder of images.

First, set up the alpha channel storage document:

1. Open the image that will be the master storage document for the alpha channel.
2. Load the alpha channel as a selection (for example, Command-click/Ctrl-click the alpha channel in the Channels panel).
3. Choose Select > Save Selection, name the channel, and click OK.

Then build an action that includes the following steps:

1. Start recording.
2. Choose Select > Load Selection.
3. In the Load Selection dialog box, under Source, choose the Document that contains the alpha channel you want, and make sure the name of the selected Channel is also the right one, then click OK.
4. The selection is now active, so add any other processing steps that need to be masked through it such as an adjustment layer.
5. Save the document.
6. Close the document.
7. Stop recording.

Finally, run it as a Batch action (or set it up similarly in Image Processor):

1. Close all documents except the one storing the alpha channel.
2. Choose File > Automate > Batch.
3. Select the action.
4. For Source, select Folder, then click the Choose button and point it to the folder full of images to process.
5. Click OK, and that should run the action on all the images in the folder.

[drferry]

Wow! Two great ideas!  Thanks so much!  It would be even easier if a subsequent version of Photoshop allowed us to export and save alpha channels. How do we make that suggestion?

[Conrad C]

Remember, Save Selection/Load Selection do export and import alpha channels from other documents open in Photoshop, and those documents can be empty otherwise. What it sounds like you might asking for is to have a file format that is nothing but an alpha channel, which can be saved to or loaded from without having to be open. If you do want something that isn’t already available, you can submit it at the official Photoshop Feedback website. Unlike the open-ended user discussions on this forum, the Feedback Site allows specific requests to be tracked and voted on, and for the popular ones, Adobe staff sometimes provide a status update and may post there when a request or bug report is actually resolved in the application.

One other thing about loading alpha channels: Both documents must be the same pixel width and height.

[Lumigraphics]

Looking into using Split Channels to see if that fits your need.