SantaFeBill

@markbowen - Apparently that is a Mac-only feature. There's no 'Separated Mode' option under 'Window' in the PC version. But thanks for the suggestion. Perhaps in the next PC update?

I think I've figured out a workflow that gets the result I want using 'Erase'. I need to try it on a few more images to be sure.

I think I'm beginning to understand. 'Erase' in AP doesn't work as it does in other programs I've used. In those programs, the erase toll automatically picks up pixels from the surrounding area and replaces the pixels in the erased area with them. In AP, 'Erase' works by picking up pixels from another layer and replacing the erased area with them. What the replacement looks like depends on what is in the other layer. That seems to be what you, Alfred, have said and also what I understand is in the video that Cecil recommended. However, I still have a problem. I open the TIF file I want to modify. AP automatically adds a Background pixel layer. I then go to 'Layer' and click on 'New Fill Layer'. A fill layer is added at the top of the layer stack. I then uncheck the fill layer (only way I can get back to the Background layer to work on it). I click on the Erase Brush Tool. Again, everything works - I can change opacity etc. and can drag and paint over the area I want erased. The checkered area appears, but the color of the fill mask doesn't appear in the erased area - and that's it. Nothing else happens, and as I said in my original post, I can't find any action/keystroke/mouse click that makes anything happen. Obviously, either there's something about my hardware that AP doesn't like, or, much more likely, there's just some very basic things about working in AP that, lacking experience with Photoshop, that I just don't get - and in the few days left in my trial period - aren't going to get. Too bad. I haven't been satisfied with the way erasing functions in my other main programs - although they work as advertised. I had hoped that AP might be the solution. BTW Alfred, you live in a magnificent country. Spent too short a time there 2005 - Plockton and a short while in Edinburgh. (My maternal grandmother's family were Campbells, traced back to Scotland.) Thanks to both of you for trying to help. Also, I did watch a number of videos on YouTube - could never get the good clean results shown in them - always artifacts left.

If I use the Erase tool on the first pixel layer - the one that is created when I open a TIF file for editing - I can select the area I want to erase - the checkered area appears as I move the mouse, and I can control where it appears. The options for controlling opacity etc. work as expected. But how do I complete the erasure? In one other program I use, the erasure starts as soon as I release the mouse button. (Not sure that's the best idea, but at least it finishes.) In another program, pressing <Enter> starts and completes the erasure. But in AP, no key press or mouse action that I've found does anything. The area selected stays selected, and nothing more happens. I tried 'Save' and then 'Close'. When I reopen the image, the checkered selected area to be erased is still there, and still nothing has changed - the area hasn't been erased. Cloning, OTOH, works as expected. BTW, I looked at several videos (not all by any means) on YouTube about erasing in AP. They seemed to just assume that the erasure would complete, w.o.explicitly saying how this is accomplished. Windows 7 Pro 64-bit. Quadro K620, latest drivers.

Where is 'Image>Duplicate'? How do you invoke that action in AP? I've looked extensively in the Help - there's no mention there, tried every thing on the screen (drop-downs from the items ('File' etc.) at the top of the screen, the options at the left, options that you get when you click on a layer, etc.) and I don't find this anywhere.

Agreed that this would be an important improvement. One of the most useful features in DxO PL2 is the ability to quickly create a duplicate and then work on that, preserving the original unchanged.

AP is a powerful therefore complex program. There is much to explore and learn. For me, not coming from a Photoshop background, 10 days won't let me really tell whether the program is right for me. What I've see so far looks quite good - but I need more time. DxO PL2, ACDSee Ultimate 2019, and On1 PhotoRAW 2019 all offer a 30-day trial period. I urge you to do the same. It would be a shame to miss out on a very useful tool simply for lack of time to properly evaluate it.