Photo magic with Gimp

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Katja is the German editor of LinuxFocus. She likes Tux, computer graphics, film & photography and the sea. Her homepage can be found here.

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Holiday season is over and you have your digital photos on your hard disk. Now it's time to give them a final touch with The Gimp. In this article we show you with several examples what you can do to enhance your photos with The Gimp (the latest stable version when I wrote this was Gimp 1.2.5).

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Photo magic with Gimp

Colour Correction

Sometimes a photo looks a bit colourless, it is too light or too dark or there are other reasons why a colour correction would help the photo. To improve the colours of your photos you can use the tools that you find in the menu under Image->Colors (you get to the menu by right clicking in the image that was opened with the Gimp). Most of the time there will be a preview field that you can tick to make the changes viewable at once. If you click on Reset the changes won't affect your image and even if you already clicked "okay" you can still get your old image back by clicking crtl+z.

However to try out several effects and compare them with each other it is better to make one or several duplicates of your photo (Image->Duplicate) before you apply the canges to them.

It's always the best if you keep a copy of your original. Perhaps you won't like the changes that you did anymore next year or you want to try out something else. Then you will be glad to still have the original. So it's always better to save the changed photo with a slightly different name.

The Curves-Tool

If the photo is a bit too light or too dark you can work on it with the Curves-Tool (Image->Colors->Curves). If you move the curve a bit up the photo gets a bit lighter and if you move it a bit down it gets darker. But you also have the possibility to change the colour values of red, green and blue individually. Because of this the curves tool is very well suited to deal with colour cast. In the example the shop in St.Tropez is a bit too blue:

[Shop in St. Tropez that is a bit too blue]

Fig.1 Shop in St. Tropez that is a bit too blue [The Curvestool]

Fig.2 The Curvestool [The shop in St. Tropez]

Fig.3 The shop in St. Tropez

The Levels-Tool

Some photos don't use the entire colour range. Therefore they tend to look a bit gray. That's the time for the levels tool. Often it will already be sufficient to go to Image->Colors->Levels and click Auto. If you are not satisfied with the result you can also easily do it by hand: You look at the curves and move the arrows so that the space at the ends isn't empty anymore. If Value is selected above the tool will be applied to the whole picture but you can also do it separately for each colour which often gives a better result. By moving the two arrows at the ends often the whole picture gets a bit darker which can be corrected by moving the arrow between them accordingly. [View from Mont Royal on Montreal]

Fig.4 View from Mont Royal on Montreal on a muddy day [View from Mont Royal on Montreal after working on the photo with Gimp]

Fig.5 View from Mont Royal on Montreal after working on the photo with Gimp (Image --> Color-->Levels, then click on "auto",Image-->Color-->Hue-Saturation, moving of the sliders to the right with "master" being ticked and Filter-->Enhance-->Unsharp Mask (see below))

More colourful looking colours and warmer looking photos

If a photo is just a bit colourless because it was a muddy day while the colour range is okay you can get a more colourful picture with Image->Colors->Auto->Color Enhance. The photo will look warmer that way so that you might like to try this tool even with already good looking photos. With some photos the colors look a bit unnatural though. If you still want a warmer looking photo you can try Hue-Saturation and increase the saturation there (master needs to be clicked to get the effect for the whole image).

[A photo of Kasteel Erenstein that is too dark]

Fig.6 A photo of Kasteel Erenstein that is too dark [Photo of Kasteel Erenstein after applying the Levels-Tool]

Abb.7 Photo of Kasteel Erenstein after applying the Levels-Tool to the image (you could have used the Curvestool as well), the photo is lighter now but looks a bit colourless [The levels tool]

Fig.8 The levels tool without having made any changes, with the arrows moved and after applying the tool [Photo of Kasteel Erenstein after the additional application of Enhance Colors]

Fig.9 Photo of Kasteel Erenstein after the additional application of Enhance Colors (Image->Colors->Auto->Enhance Colors), the photo is still a bit dark in the foreground but the castle itself is well lighted and gets the attention of the viewer

Increasing the sharpness of your photo

Some digital photos are just a little bit unfocused or the photo lost focus by applying some other tools to it. To increase the sharpness of your image there are the tools unsharp mask and sharpen in The Gimp. Both can be found under Filters->Enhance. With unsharp mask you often get a better result as this method improves on the edges. In many cases you will already be satisfied if you apply it with its default values.

Fig.10 Black and white picture of row of houses in Liège [The row of houses after applying the Unsharp Mask]

Fig.11 The row of houses after applying the Unsharp Mask You should only use this filters after you have applied all other changes as some tools (e.g. scaling of the photo) can change the sharpness of the image.

Reducing the depth of focus

Sometimes it's difficult to take a picture with your digital that has the focus on the foreground and your object you focus on and a blurred background. Gimp can help you to reach this effect afterwards.

For this you select the part of the photo that you want to be sharp with the intelligent scissors (that's the tool in the main menu that actually looks like a pair of scissors). You make some points around the object that you want to select. The intelligent scissors find the outline themselves. Therefore it is important to make more points in those areas where the object doesn't have a big contrast to its environment. To make the selection effective click on the first point that you made again, the scissors change into a square, now you click somewhere inside your object. Now you can see the selection. Next you sharpen it a bit. For this you click on Filters-->Enhance-->Unsharp Mask (or Sharpen). After that you invert the selection (Select-->Invert) and blur the background. To do this you go to Filters->Blur and choose the blur tool that you like best. Sometimes you won't like the transition between the sharp and blurred areas. In that case you can select the blur tool and draw around the outline as you would do with a paint brush.

Fig.12 Bear with Jessica at the Fête des Enfants in Montreal [Bear with Jessica with a blurred background]

Fig.13 Bear with Jessica at the Fête des Enfants in Montreal with a blurred background

Blurred vision: Soft looking photos and Movement

With a non-digital camera you can get a soft looking image by using long shutter speeds. Of course you can create this effect with the Gimp afterwards. The blur tools can very well be used for this. The photo gets a softer look and may even look kind of romantic. Selective Gaussian Blur (Filters->Blur->Selective Gaussian Blur) is best to use here as the blur filter will only be applied to areas that don't have a big contrast.

Fig.14 Kasteel Erenstein looking softer after applying Selective Gaussian Blur and a frame added with Script Fu-->Decor-->Fuzzy Border

If you want to create an impression of movement the Motion Blur Filter (Filters-->Blur-->Motion Blur) will do best. The original looks like this: [Tux in Oldtimer]

Abb.15 Tux in Oldtimer And after applying Filters-->Blur-->Motion Blur with Linear as type of blur and with the Length 20 and Angle 45 you get this racing Tux: [racing Tux in Oldtimer]

Abb.16 racing Tux in Oldtimer

When less is more: Removing disturbing objects

One characteristic of a good photo is that is has a subject it focuses on and not so many other things to distract or confuse the viewer (except of course this was in the intension of the photographer...).

So it can happen that one or more objects in an image disturb the overall impression of the picture and therefore it would be better to remove them. To do this you can use the clone tool (that's the button in the main menu that looks like a stamp). If you have selected the clone tool you click with your mouse in the area that is to be cloned while you hold the Ctrl-key down.Then you release the key and click with the mouse in the area that you want to paint over. Now you can use the clone tool the same way you would use a paint brush. Sometimes you will get a more natural looking picture if you define a new cloning area several times. And practise makes the master here!

Certain mistakes in a photo like a tree that grows out of a person can also be corrected this way.

Fig.17 Photo of my grandfather [Photo of my grandfather after working on it with the clone tool]

Fig.18 Photo of my grandfather after working on it with the clone tool

Framing the photo

To get more focus and attention to your image you can give it a frame. Gimp offers numberous possibilities for this.

Fig.19 Photo of Wilhelmshaven with a red frame First of all you can give your photo an ordinary frame. For this you choose Script Fu --> Decor --> Add Border. Now you need to decide the width of the frame and its colour. Then click on okay and The Gimp gives the picture a frame whereby the resulting picture will be increased.

A very beautiful frame you get by usingScript Fu --> Decor --> Fuzzy Border. This is actually my favourite frame. But of course everything depends on the motive of the photo. [Flowers with Fuzzy Border]

Fig.20 Flowers with Fuzzy Border Another possibility is to select that part of the image that you really want to see. After selecting it with the selection tool you invert the selection (Selection ->Invert) and change e.g. the lightness of the border (e.g. with the curves tool),etc..

[Photo of St. Tropez with a lighter border]

Fig.21 Photo of St. Tropez with a lighter border If you like this or not is of course a matter of your taste.

Inserting text

Sometimes a picture will only become something special or personal by adding some text at the right place. In the picture below the text was simply written over the name of the bridge that was hardly readable. With the colour picker (that's the icon between the Texttool and the bucket) the colour of the decoration of the bridge was chosen. Then the font elfring elitelight was chosen in the text tool of Gimp and the text was inserted into the photo.

[Photo with inserted text]

Fig.22 Here is the photo that only got a special personal photo after inserting the text.

Of course The Gimp can't always do miracles and change a bad photo into a good looking one. And it's also not possible to write a cookbook with recipes for every photo as each tool has a different effect on different photos. But still I hope that this article will be useful for you to get the best out of your pictures!

Have fun and happy gimping! :)

References

gimp.org: Here you find documentation, you can download The Gimp etc.
On this site you find some very good tutorials on manipulating photos with The Gimp: http://cs.uhh.hawaii.edu/~jeschke/photography/articles/gimp/