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Using Gimp to rescue an underexposed portrait photograph

Using Gimp to rescue an underexposed portrait photograph - This tutorial will show you how to fix the lighting in an outdoor photograph using GIMP's colour and sharpening tools while maintaining a natural end result.

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Gimp before and afterSometimes the picture you take is not the exactly how you want it to be for reasons beyond your control. Here the natural lighting has caused the background to be brighter than the intended focus of the image, and as such the eye is drawn more to the surrounding details rather than the central figure.

For this tutorial I am using a stock photograph by Nichola Robinson, an Australian photographer and artist, if you wish to work alongside this tutorial then you can download the original image from here and click on the image to enlarge it before saving it.

1 The first thing we want to do is brighten the model, as the shadows covering her are currently far too dark, so click the highlighted button to duplicate the first layer.

Then double click the name of the layer to edit it, this is a good habit to get into so as to avoid confusion when attempting more elaborate, multi-layered projects. I’ve called this layer ‘Foreground’ since this is what I will be using it for.

Gimp duplicate layer
2 Open Colours>Levels to access the levels menu. You can use this to brighten and darken an image, drag the white arrow under the input levels quite a way to the left. There is a spike of data at the end of the graph, but that is the sky which we can ignore for now; we want to brighten the data closer to the start of the graph in order to brighten the shadows and our model. The background is far too bright after applying this change, so we will remedy this next Gimp levels adjustment

3 Right click the ‘foreground’ layer in the layers dialogue box, and select ‘Add Layer Mask’ and select ‘Black (full transparency). Use the bBrush tool to paint the model white in the layer mask to make it visible over the background image. Here I am using brush (19) which is a large, soft brush to avoid making the difference between the model and the background too stark.

A useful shortcut to remember here is that ‘X’ swaps between your brush's background and foreground colours, allowing you to quickly correct any areas where you may have slipped in your layer mask.

Use the square bracket [ or ] keys to increase or decrease the size of your brush as required for more difficult areas to ensure the bright version of the background is fully hidden.

Gimp brush

Gimp unsharp mask4 Now the model looks too crisp compared to the scenery around her. It's as if she has been artificially placed in the photo. To minimise this we will now edit the background so that the two are integrated with a greater degree of success.

Duplicate the background layer again and rename the new layer, I’m using ‘BG edit’ for brevity’s sake. This is so we don’t have to edit the original photo directly, meaning we can delete the layer and start again if we make a mistake that cannot be undone.

This is another good habit to get into, although everything we’re doing here can be undone easily with ctrl+z and redone with ctrl+y.

We are going to apply the Unsharp Mask filter to the new layer in order to try to make it a tad crisper, without making it fight with the model for our attention. Open Filters>Enhance>Unsharp Mask to begin using the filter.

Gimp levels adjustment

5 The Unsharp Mask tool sharpens the image, but is a more specific version of the general sharpening tool. The Radius slider controls how large the areas that are sharpened will be, so a smaller value will allow for greater detail and a larger value will create a lesser degree of detail.

We don’t want the background to be too detailed, so don’t set the Radius too low. The most important value in this tool is the Threshold, which controls how sensitive the mask is, if set too high then your image will sharpen in almost every location and if it is set too low then very little will be affected.

This is used to avoid sharpening everything in the image including distortions and grain, so set this level high enough to get a noticeable effect but avoid increasing distortion where possible. Here we are bringing some added definition to the trees in the background, but avoiding making them too distracting or distorted.

6 Now the background colours look very intense and artificial, so we are going to correct them using the Hue and Saturation tool. Open Colour>Hue and Saturation.

Here I have moved the Hue slightly to the left to make the intense yellow in the background slightly more orange. Then I increased the Lightness by a small amount and reduced the Saturation a bit to make the colours less vivid and artificial.

Gimp colour adjustment

Gimp levels adjustment

7 Nichola’s dress could do with being a bit more detailed, so we are going to make the pattern and shadows more prominent by overlaying it with a copy of itself and then colouring it using the brush. Duplicate the ‘foreground layer’ and edit the layer name to ‘Dress’, change the layer mode to ‘Overlay’ and the resulting difference should be subtle yet still apparent. Then use the Layer Mask tool to hide her skin as before, otherwise it will be noticeably darker.

Gimp dress detail

8 I then used a brown colour to return some colour to the dress, painting into the Overlay channel using the Brush tool. Should you lose the colour you are using at any point you can hold control and click with the left mouse button to use the colour selector on one of the areas you have already painted.

Gimp colour

Gimp soft glow

9 Finally use the Soft Glow tool in Filters>Artistic>Soft glow to increase the brightness of the sky and add a ‘bloom’ effect in the ‘BG edit’ layer. This emulates the effect of looking into a bright light from a dark location, which is how this picture was taken, so create a bloom that is realistic, but doesn’t wash out the colour too much.

The Glow radius value controls how far into objects the light bleeds, with the Brightness and Sharpness controls helping you to manage the way this bleeding will look and how much detail will remain in the objects that are affected. Apply the glow effect and your edited picture is now ready to be flattened and exported.

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Tried to follow this one, but could not view the face in the add layer mask in 3.....probably my bad though Smile

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