How to correct photos which were overexposed at the edges only?

Question

I'm dealing with a set of photos where a model was photographed against a white backdrop. The problem is that due to the setup, way too much light reflected off the backdrop. So the model's face (for instance) is not overexposed. However, the light coming off the backdrop is so intense, the model's edges are lost, as they fade into white much too quickly, leaving no definable "edge".

I know it may be hopeless, but are there any things to try to bring back some edges without underexposing the rest of the model (the lighting is essentially perfect everywhere else). The photos are in RAW, and I have Photoshop & GIMP for post-processing.

Answer 1

You don't mention if you shot in RAW or JPEG but if it's the former you'll have a lot more latitude in trying to rescue them.

If you did shoot RAW, open your files in Photoshop Camera Raw and pull the Recovery slider all the way up to 100. That will show you how far Photoshop is able to rectify the blown highlights from your RAW data. (Unfortunately if you shot JPEG then this method won't work for this level of overexposure.) If you're lucky, you'll see some definition returning around the edges of your subject and you can adjust the Recovery slider to fine tune it.

If that doesn't work (either on RAW images or because they're JPEGs) your next stop is the Exposure adjustment layer. Here's a good guide to adjustment layers: Exposure is no. 4, some way down the page. First try reducing the Exposure slider to darken the whole image (I know you want to preserve your skin tones - bear with me!). Does that help recover any of the definition around the edges? If so, now use the Offset slider to try brightening the midtones again.

If neither of these methods works, I'm afraid it may be that the detail has just gone and there's no way to recover it.

Answer 2

What you want is to decrease the amount of light coming off your backdrop so that the backdrop itself is bright enough to appear the way you want it (presumably to clip your sensor so that you get a pure white look) but not bright enough to significantly light up / overexpose your model itself with reflected light.

In your example photo, it looks like whatever light you have on your background is set way too high. You can probably decrease your backdrop light power by a stop or three and still have it clip to pure-white.

You could also add more distance between your model and the background. Light intensity decreases with the square of the distance from the source. Note that this will also change your background-to-camera distance (assuming your model-to-camera distance is constant) so it will also effectively decrease the amount of light from the background hitting your camera (effectively making it darker).

Lastly: if you really want to eliminate reflections from your background on your model, consider really dropping down the power on your light (even below your clipping level) and then changing the background to flat-white in post production (Photoshop etc). This can get tricky around the edges (especially hair) but sometimes it's worth trying.

Answer 3

You can darken parts of an image in Photoshop by adding adjustment layers and then using the mask to show or hide parts of each adjustment layer. Here is a tutorial for adding an adjustment layer: http://psd.tutsplus.com/articles/techniques/a-basic-guide-to-photoshop-cs4-adjustment-layers/ and here is basic info about adjustment layers: http://www.adobe.com/designcenter-archive/tutorials/adjlayerbasics/

You'll probably get the most help here from a LEVELS adjustment layer, though the CURVES adjustment has presets for darkening and increasing contrast (when you're in the curves dialog box, use the drop down menu next to the word, CURVES, and select "Darker"). I tried to post tutorials for levels and curves but I don't have enough reputation points to post more than two links. But if you search for levels and curve adjustment layers, you'll find them.

Once you add an adjustment layer (say for LEVELS), you can hide part of that layer using the mask. Every adjustment layer will have a white rectangle on the layer palette. That white rectangle is a mask. If you use a brush (or the gradient tool) to paint black onto that mask, then part of that layer will be hidden. If you use the gradient tool on the mask and add a gradient from black to white, you'll get a gradation of transparency on that layer.

If you only need to apply an adjustment layer to a small part of the image (say just the elbow and part of the model's face), after you create the adjustment layer, click that white rectangle and then go to Edit>Fill and fill with black. That will hide the whole adjustment layer. When it comes to masks, black hides and white reveals. Then with the mask (the white rectangle) still selected, use a brush (with close to zero percent hardness) to paint white on the parts of the photo where you want the adjustment layer to show. So if you created an adjustment layer for LEVELS that darkens the image, use your brush to paint on the parts of the image that you want to darken. Again, I don't have enough points to post a tutorial, but if you search for "Photoshop Mask" you'll find tutorials on how to do this. You can also adjust the transparency of the adjustment layer in the layers palette to make the effect more subtle.

BTW, you can also use adjustment layers to increase or decrease color saturation, change the hue, and do all kinds of things. And you can use the masks to show or hide parts of all the adjustment layers you add. You can also add a mask to regular layers in photoshop to hide parts of a layer.

Answer 4

If there is enough data in the RAW file that you can retrieve the edges, even at the cost of the overall exposure, then you can certainly do it. I'm only familiar with Photoshop to any real depth, but I'm sure you can do something similar in the Gimp.

You will need two developments of your RAW file. One, you already have — the one where the optimum result has been achieved for most of the image. You will need a second version of the picture where the edges of the subject are distinct from the background, even if that means that most of the picture looks horribly dark. If you can keep the background pure white, that would mean bonus points, and if there's enough there to make the "lost" edges significantly different from white (say ten or more levels, with some actual colour), then you've already won the lottery. (Oh, and make them both 16-bit; that will allow you to recover without posterizing.)

Put the dark version on a level above the more correct version. Then go to the "Channels" panel and CTRL- or Command-click on the RGB channel. That will create a selection based on the luminance values in the dark image. (The marching ants will show where the 50% level is; don't worry about them.) Then go back to the layers panel and create a Curves adjustment layer. It will automatically get a luminance mask because there was a selection active when the layer was created. The mask should look like a black-and-white version of the darker image. This will make the curve you later create affect the highlights much more strongly than the midtones and shadows, and in conjunction with the curve itself will allow you to get some really fine control over the values.

Of course, that means that if you bring down the extreme highlights, you're going to lose your white background as well. You can fix that. Go back to the Channels panel and CTRL-click on the RGB to make the same luminance selection. Now, go back to the Layers panel, select the curves layer, and do a Create Group from layers. It will have its own mask, also based on the luminance values. Go to the mask and invert it (CTRL+I). You can use Levels (CTRL+L) to make most of the subject part white, leaving the background black, then use a paintbrush to finish the job/fill in the holes.

Now you have a curve available that will only affect the brightest part of the image that isn't the background. You can hide the dark version of the picture for now, and make the adjustments that bring the subject edges (and overly-light areas) back. If you find that the effect is spilling over into areas you don't want it to touch, you can put your existing group into another group (this time with no selection active) and use a soft black paintbrush on a low opacity to paint out the adjustments you don't want.

In a worst-case scenario, where colour can't be retrieved from your "good" development, you can use an intermediate version of the image with the same luminance masking and manual masking tricks to overlay good colour data on only the brightest parts of the image that aren't background, and then adjust the opacity of that overlay to get the result you want. It's a large chunk of work, but not compared to a re-shoot, and it will give you a much greater degree of control over the process than a RAW processor alone (or any global adjustments, for that matter) can give you.