Edge shadow on painting from lighting

I guess I forgot to mention I no longer have access to the painting and my options were very limited in shooting it in situ having to have a black cloth up to block reflections limiting the positioning of both of my lights.  Had I the opportunity to shoot it again I would have tried to position my lights to get the same amount of light in the corners despite reflections for some of the exposures and tried to blend them.  But even if I could do that I would still have the problem of that line that appears whenever I try to blend them.  I guess what I was trying to ask was a more specific way to try and address this line and problems blending in post.  Cropping the piece itself was also not an option.

Any thoughts on specifically how to use the lighten blend mode and masks to accomplish brightening this area without getting a line? 

Any tutorials out there that might help? I did use a curves adjustment layer on the shadows and that helped.  But I found it impossible to blend in the shadow from an overexposed image that had lighter shadows. 

I assume you have a light on both sides. Take three exposures, one with both lights on, and two with one light turned off. Increase ISO a full stop to compensate. Then it's fairly straightforward to use soft masks and lighten blend mode to lift only the shadow parts, leaving the main area unaffected.

In the pre-digital era you had to use very large soft boxes to soften the shadows. You couldn't get rid of them, but soft shadows are a lot more visually acceptable. This increases the risk of unwanted reflections significantly, so great care is required in positioning the lights. You also had to use polarizing film on the lights, and a polarizer on the lens rotated 90 degrees (cross-polarized light).

If you can't get rid of the shadows, it may sometimes be better to light from above.

I don't know your original equipment set up, but I still hold to my original comment about moving the lights and using lighten blend mode to eliminate the shadow. Especially since the painting was suspended.  I used to do this all the time with my work.

'Light Science & Magic' by Fil Hunter is the de facto book for this and, pretty much, most other photography lighting situations.  It is up to edition 5 now, but earlier editions are available as PDF files. Pages 52 onward covers photographing paintings.

I actually use a slightly different approach I learned from either David Hobby or Jo McNally.  I think it was from Joe's first book 'The Moment it Clicks' but whoever I loaned it to forgot to return it.  This approach makes use of light fall off with distance and the light's axis, and takes a bit of balancing, but you aim the light's axis at the far side of the canvas, and adjust the distance and angle so the fall off towards the edge of the beam on the closest side of the painting, matches the fall off with distance with the furthest side.  You do this with two diffuse light sources, which gives you a lot of lee way so it's not hard to get right.

If your artwork was behind glass, then you have done well to avoid reflections in the glass I'd say, but your light source is way too small judging from the very shallow Shadow Edge Transfer.  I'd also hazard a guess that you only used one light?

Anyway, to fix this particular situation, then as Nancy and Chuck have said, sacrifice the shadow area.

There are any number of approaches. Quick and dirty would be to select the good area of the artwork

And stretch it with Free Transform to cover the shadow area

Not only could I not unframe the piece but it was behind glass and hanging from strings.  It couldn't be moved except for the gentle sway it had going from hanging.

Trust me, I also do this for a living and I tried everything.  I took some shots over exposing the piece and thus exposing the shadows correctly but any time I try to line them, or mask them, or anything I get a line.  I'm really stuck.  I can't crop the painting.

Chuck how did you get that result with a curve adjustment layer? 

Yeah, that shadow. I do this for a living, so I run into this a lot.

If you can't take it out of the frame, then Turn the painting and shoot it again. Take a few shots if you have to, but turn the painting, not the lights. Make sure your light is even and unmoved. Once you have your shots you can rotate them , so they're all the same position on screen. Now crop out the shadow areas and use the panorama stitching function to stitch it back together. (file -> Automate -> Photomerge).

Another thing you can do is to crop the image so there's no frame, and then you can put a rectangular marque around the shadow, and then hit the delete key and select content aware. There isn't anything too important in the shadow of this particular piece, so you'll get a natural looking fix.

The most obvious thing is to use the gradient tool to lighten that shadow, but I can assure you it will never work well. Ever. Try the first two things, and one of them should work for you.

I would agree with Nancy about removing the canvas, or taking several photos and move the lights around, so that you can fill in the dark area and blend the exposures. But if you have to work with this image, you can use curves and very carefully mask in the corrections.

Next time remove the canvas from it's frame BEFORE you shoot the photograph.  There isn't much pixel data left to work with.  I would probably crop it.