GIMP Tutorials


Vignettes are great, yes they can be regarded as a lens defect, but sometimes they can add that certain something to an image. I have seen other tutorials on the web which are very similar to this one, differing only in that I like to use  Layer Modes for most of my vignettes. I particularly like the boost to contrast and saturation that the Multiply mode gives, I think it has a more retro feel. Anyway let’s begin.

Step 1. Open your image in GIMP, right click on the “Background” layer and select Duplicate Layer. Note that this new layer has become the active layer, as denoted by the white border.


Step 2. Right click on the new layer “Background copy” and select Edit Layer Attributes, enter the new name “Vignette” and select OK.


Step 3. Right click on the “Vignette” layer and select Add Layer Mask…


Step 4. In the Layer Mask dialog box choose the default White (full opacity) and select Add.


Step 5. Select the Blend tool from the Toolbox, or by selecting Tools > Paint Tools > Blend. Ensure that your Foreground color is Black and your Background color is White. Use the default FG to BG (RGB) Gradient and change the Shape: to Radial.


Step 6. Turn OFF the visibility on the “Background” layer by clicking on the little eye icon. Then Click in the center of your image (or the main point of interest) and drag out toward the corner of your image. Sometimes you may need to go out beyond the edges of your photo as I did in this example. Repeat this step as many times as is necessary, the aim here was to make the majority of Mischa’s face transparent.

This is a great example of Layer Masks in action. White areas are treated as Opaque (solid) while Black areas of the mask are treated as Transparent. The information is still there in the layer but the mask controls what is displayed.


Step 7. The Blend tool produces a very soft transition between black and white, we can sharpen the vignette by shortening this transition. Launch the Curves tool by selecting Colors > Curves… Click to add a control point in the center of the graph and then raise the right hand portion and lower the left hand portion. You may need to experiment a little here to see what works.


Step 8. Turn ON the visibility of the “Background” layer by clicking the little eye icon and change the Layer Mode: to Multiply


That’s it. one nice subtle vignette effect. I recommend that you experiment with some of the other Modes, Overlay can work well, Burn can give massive saturation boost and Subtract can give a very dark vignette. Also experiment with the opacity to lessen the effect.

If you are still not quite getting the vignette you want try changing the Mode back to Normal and use the Brightness/Contrast, Levels or Curves tools to manually darken the “Vignette” layer. If you are trying this make sure that you select the “Vignette” layer (as in the actual image) rather than the Layer Mask, the white border will tell you which is active.

Happy GIMPin’




Haven’t posted in ages, too many irons in the fire me thinks. I am going to show a very simple method of enhancing the existing colours in a digital photo using GIMP. This tutorial is aimed at those who are new to GIMP and new to photo editing. This is based on GIMP version 2.6.4 and requires no additional scripts or plug-ins beyond the basic default installation.

Here’s a picture I took while out walking the dog one day, some rather sorry looking birch trees. My aim is to enhance the Yellows to give a nice autumnal feel and also to give a boost to the Greens, so let’s begin.

1. Open your image and from the Colors dropdown menu select Colors > Hue-Saturation…

2. Select the Yellow radio button and move the Saturation slider to the right to increase the stauration, in this example I have increased the saturation of the yellows by 20 as I felt that it suited this image.


3. Select the Green radio button and again move the saturation slider to the right, this time I have increased the saturation by 30. When you are happy with the results click OK.


Well that was easy, I rarely use the Hue and Lightness sliders so I am not going to take the time to explain what they do, but feel free to experiment with them or check the GIMP Help, if you haven’t installed the Help system they are all available on

The Hue-Saturation tool really is quite useful, some possible ways you might use this tool of your own photos include enhancing blue skies, enhancing reds and yellows in sunsets, reducing red in faces (particularly sunburnt one’s). This list of possible uses is really only limited by you imagination. Here’s an example in which I have used the Hue-Saturation tool to desaturate everything but Blue.


Happy GIMPin’



GIMP gives us a number of options for influencing the tone and colour of our photos, however “Levels” and “Curves” are the most versatile and hence the ones which you will use almost exclusively. Most of these other tools are pretty self explanatory and can be found in the Colors dropdown menu, there are also some fully automatic tools in Colors > Auto. There are also some new options in GIMP 2.6 in the form of GEGL Operations, these can be accessed by selecting Tools > GEGL Operation… and selecting from the dropdown, I’m particularly pleased with the color-temperature tool.

I had intended to write seperate tutorials for Tone and Colour and indeed the “Levels” and “Curves” tools, however I have chosen to go a different route. I shall instead improve both the Tone and Colour together, working through Levels and on to Curves as I do so. Hopefully this approach will be educational, as it will allow you to see how changes made in Levels are implemented in Curves.

So here is a shot from an underground passageway in an old ruin near where I live, you can see that the image is washed out and lacks contrast, there is also a blue colour cast on the stone work and rubble in the foreground. So lets begin, I am assuming that you understand the basics of the image Histogram, if not please read Histograms: A Levels and Curves Primer first.

In order to make this followable I am going to split the process into three parts, Tonal Range, Whitebalance (colour cast) and Tone (brightness/contrast).

1. Launch the Levels tool by selecting Colors > Levels… and try our automatic options. Auto Levels will work very well on the majority of photos (this is one example where it fails, Auto Levels results in far too much contrast and does little to remedy the colour cast). If Auto fails click on Cancel and relaunch the Levels tool again.

2. If you are happy with the colour in your image you may wish to skip ahead to step 3.  This is certainyl not the case here so we’ll try the three Colour Picker buttons, selecting a Black point from inside the chimney, a White point from the brightest point on the wall outside and a Gray point from the stonework gives quite good results on this image, however it failed to fully get rid of the colour cast. However it does give us a good basis for further work.


Hint: You do not need to use all three colour pickers, good results can sometimes come from using two or even just one. Also I usually use the Gray picker last, the reason for this is that it can be difficult to tell what is neutral grey, hence the grey step may have to be repeated.

Tonal Range

3. Launch the Levels tools by selecting Colors > Levels… We can see that the Value channel histogram does not extent to either end of the scale, this compressed tonal range is a reflection of the washed out, low contrast nature of the image, so we need to increase the tonal range.

4. Grab the left triangle pointer and drag it out to the start of the histogram graph, this will remap the tones in our image so that the darkest tones will be rendered as pure black.

5. Most images will contain some white areas so I would normally drag the right pointer to the right edge of the graph, however in this case I know that this image contains little or no white, nor do I want it to, so grab the right triangle pointer and drag it slightly to the right. The aim it so increase the tonal range without remapping the brightest tones to pure white.

Hint: The center triangle pointer represents the midtones, moving this to the left or right will darken or lighten the image respectively.


6. Take a look at the histograms for the Red, Green and Blue channels. Note the changes made by the use of the three color picker buttons, the tonal range has been increased and the center triangle pointer has been moved away from the default 1.00 position, thus increasing Red and Green in the midtones and reducing Blue.


Hint: If your histogram is very flat and shows no discernible peaks or detail try switching the mode from Linear to Logarithmic, I have circled the buttons on the above graphic for the Red channel.

Colour Cast

7. Time to get rid of that colour cast, select the Blue channel from the dropdown in the Levels dialog box.

8. Unfortunately in this case moving the center pointer further to the right (reducing blue) simply makes the image much too green, it’s time for Curves to come to our rescue. Launch the Curves tool by selecting the Edit these setting as Curves button in the Levels dialog box.

9. Take the time to look at the Curve for the Value channel. Observe that the graph is no longer the 45 degree angle we expected. The top and bottom of the graph have been moved inward, this is the curves representation of the increase to tonal range we made earlier using Levels.


10. Now take a look at the curves for the Red, Green and Blue channels, again we can see the tonal range increase but this time we can also see the center of the curves has been raised for Red and Green and lowered for Blue. This is the curves representation of the changes made using the three Color Picker buttons back at the beginning.


11. We wish to remove further blue from the highlight (brighter) areas so select the Blue channel. Grab the top right of the curves and drag it down until the line becomes diagonal.

tnc_7_diagonalIt is probobly good practice to repeat this step for the Red and Green channels also, however I am not going to do it in this case for one very simple reason. Histograms are neither right nor wrong, I am happy enough with how the blue has been removed while keeping the red of the brickwork in the ceiling and the green of the mossy walls. My attitude would be that it is better to make any edits based on how the image looks rather than upon what may be suggested by the histogram.


12. As a final step we will alter the tone slightly so as to better match my memory of what is basically a damp undergroung passageway. Select the Value channel and click of the center of the curve to create a control point (circled below), next click on an area in the lower (dark) portion of the curve and drag it downwards slightly. Next click of an area in the upper (bright) oprtion of the curve and rise it slighly. This is the classic “S” curve you will frequently hear mention of, we have used it here to darken the dark areas while simutaneouly brightening the brighter areas. This is the real power of curves, it gives us very fine control by allowing us to affect as many control points as we see fit, 5 in this example.

tnc_8_toneHint: Soft gentle curves tend to work best. One way to make very small adjustments easier is to use the arrow keys (on PC, I’ll check this in Ubuntu), the up and down keys move the selected control point up and down, while the left and right arrow keys allow us to scroll through control points.

13. When you are finished click OK.

Levels and Curves can be  a tricky at first, however any time you put into learning them will be time well spent. Unfortunately these tools give us so much control that it now becomes difficult to know when to stop, I’m thinking that I overdone the contrast a little in this example and am considering starting again, but it should serve for demonstrative purposes.

Happy GIMPin’


Gimp gives us a number of tools for controlling the tone and colour of our images, but the undisputed kings are Levels and Curves. The vast majority of our photo editing needs will be catered for by either (or both) of these tools so they are quite important. This is just a primer to introduce some concepts, I’ll write a post showing Levels and Curves in action soon.

In order to use both Levels and Curves effectively you will need to understand the image Histogram, Sounds complicated at first but it’s actually quite simple. the image Histogram is a graphical representation of the tones in our image, from pure black on the left, to pure white on the right. The height of the graph represents that number of pixels within the image for each of the values in between.

So why is this information important to us?. Because it tells us quite a bit about our photo.


if we see the majority of the graph clumped up on the left hand side it suggested that our photo is too dark (underexposed). If the majority of the graph is clumped on the right if suggests that our photo is too bright (overexposed).


In addition it can also tell us something else, if we see the graph spill off the right hand side it tells us that sections of our photo are “blown out” (pure white with no detail or texture), conversely if our graph is spilling off the left it tells us that our shadows have been “clipped” (pure black with no detail or texture).


Tonal Range

The image Histogram can also tell us about the tonal range of our photo. If we see that our graph is clumped up somewhere in the middle and not reaching to either (or both) end of the range, then our photo has a compressed or limited tonal range (our photo only contains a subset of the possible tones). The vast majority of scenes will contain both black and white so this usually suggests a problem. Look at the histogram of any photos you have which are hazy and lack contrast, limited tonal range is probably the problem.


Colour casts

There is more than one histogram or course, there is the Value histogram (Luminosity) which gives us basic brightness information. However there is also a seperate histogram for the Red, Green and Blue channels (we’ll skip the Alpha histogram for now). We know that pure white, pure black and neutral grey should contain equal amounts of red green and blue, so if one (or more) of the colour histograms looks significantly different from the others it may suggest a colour cast. Here is the Red, Green and Blue channels from an image with a strong blue colour cast.


Hopefully you now have some idea of the usefulness of Histograms, your digital camera may well have a histogram function which can be viewed during playback, if so consider turning it on and bring the power of histograms out into the field. Note however that many cameras only show the Luminosity histogram, this is of limited use, you really need the colour histograms if you plan to use the cameras histogram as a light meter, that said even just the luminosity histogram can be informative, especially on those sunny days when you cannot see the LCD screen on your camera well.

Tip: Don’t bite off more than you can chew, concentrate on the Value histogram until you are comfortable with it, it’s probably the one you’ll use most anyway.



We are all familiar with the dreaded Red Eye in photographs. Fortunately most photo editing applications (GIMP included) have a Red Eye tool built in. Unfortunately most work by detecting red and working from there and hence fall flat on their collective faces when confronted with the green eyes which photos of dogs and other pets can be afflicted with.

This was exactly what happened to me today, anyway after some trial and error I came up with this method, it may not be perfect but it might be of some use in those situations where conventional Red Eye tools fail. Another option of course would be to select the offending colour and minimise it’s effect using the Channel Mixer tool, but I find this to be finicky process and I normally only end up changing the colour rather than elimenating it.

This photo of Lal was taken shortly before she died, she was a diabetic and the cataracts, which are a very common symptom of the disease, have caused a particularly nasty green eye effect. In this case I started by opening my file in GIMP and…

1. Zoom in on one of the eyes and select the Fuzzy Select Tool from the Toolbox and click on the eye. You will need to adjust the Threshold value until the entire green area is selected, In this example I increased the Threshold to 100. One thing I like about this method is that it does not matter if any catch lights are selected.


2. There is normally a small rim of colour just outside the area we selected. We can enlarge the selected area slightly by going to the dropdown menus and selecting Select > Grow… In the resulting dialog box choose to grow the selection by 1 pixel and click OK (you may need to use more in some cases)


3. To get rid of colour select Colors > Desaturate… Choose a desaturation option and click OK. I have used the Lightness option in this case because it produced the darkest result.


4. Launch the Curves tool by selecting Colors > Curves… Then darken the selected area by using your mouse to grab the center of the curve and drag it down and to the right.


5. Use the Clone tool from the Toolbox to fix any odd reflections there may be in the eyes, in this case reflections from Lal’s cataracts. (This step will be unnecessary in the majority of cases).


6. The transition between the selected area and the rest of the image will often be too “hard”,  select Select > Grow… and this time enlarge the selection area by 3-5 pixels (or whatever suits your image) then select OK.


7. To do the actual softening use a gaussian blur. Select Filter > Blur > Gaussian Blur… I used the default of 5, then select OK.


8. Your eye should now be done, turn off the selection with Select > None and repeat the process for the other eye.

Happy GIMPin’



How many times have you taken a photo of a building (trees can to troublesome too) and found that the walls are sloping inward as they rise. This is called “converging verticals” or “keystoning” and is the result of tilting your camera upward to get the building in frame. You can avoid it by going further back and zooming in, as you will not have to tilt the camera upward.

To correct it when it does occur is quite easy, I have selected a photo of a old ruin near where I live as it shows quite a pronounced example of this effect, unfortunately I could not go back any further due to my aversion to rusty barbed wire. To correct this, open your image and…

1. Move you mouse to the bottom of the left corner of the building, note the coordinate given at the bottom of the screen.

2. To add a guide line drop the dropdown menu select Image > Guides > New Guide. In the ‘Script-Fu New Guide’ dialog box select Vertical for the ‘Direction:’ and for the ‘Position:’ enter the coordinate you noted in step 1.

3. Repeat steps 1 & 2 to add a guide on the right hand side of the building. I added one at the back right corner because it was easier to see against the sky.

4. From the ‘Toolbox’ select the Perspective Tool and then mouse click in your image.

5. With your mouse, click and drag the top corners of your image outward. You may need to go back and forth between to two corners as moving one affects the other. When you are happy select Transform

6. Turn off the guide by selecting Image > Guides > Remove all Guides

7. Flatten your image by selecting Image > Flatten Image

Happy Gimpin’

This installment in my GIMP Beginners series is about Rotating and Cropping images (just as the title suggests). The areas covered being basic orientation (portrait vs’ landscape), straightening horizons, corrective cropping (after leveling of horizons) and cropping to a specific ratio. This tutorial is based on GIMP version 2.6.2.

Basic Orientation (portrait vs’ landscape)

So you’ve just opened your image in GIMP but you find yourself placing your head on one shoulder to see it right. There is luckily a one step fix for this problem.

1. From the dropdown menus select Image > Transform and then select Rotate 90 clockwise or counter-clockwise as appropriate.


Tip: Rotating a .JPG image in this fashion will cause some deterioration in quality. If you are editing an image for use on the internet you will need to rotate it, however if you are editing a file for printing you may wish to simply skip this step and perform your edits in the default orientation, your printer will not know any differently.

Straightening Horizons

Now check to see that the camera was level when the shot was taken, the best check for this is the horizon. If your horizon sloping to one side or all your buildings are leaning to the left or right proceed as follows.

1. Move you mouse to an area roughly in the center of the horizon and note the coordinate given at the lower left corner of the image window.


2. From the dropdown menus select Image > Guides > New Guide…

3. In the resulting ‘Script-Fu New Guide’ dialog box select Horizontal from the dropdown box and enter the number which we memorised in step 1, then click OK. (If you are using a building to test the straightness you will select Vertical from the dropdown and enter the number from the left rather than the right).


4. From the Toolbox select the Rotate tool and mouse click anywhere in your image.

5. In the ‘Rotate’ dialog box change the Angle until the horizon runs parallel to our guide, click OK when you are done.


6. Now turn off your guides by selecting Image > Guides > Remove all Guides.

Tip: If you are using a building it is best to select one from near the center of the photo. This is due to the fact that some camera lens (wideangle) may cause buildings to slope inwards as they rise, this is called “converging verticals”, I have a feeling that we’ll be coming back to this is a later installment.

Corrective Cropping

If you have rotated your image in order to straighten it corrective cropping will your next step. To do this

1. From the Toolbox select the Crop tool. To keep the cropped image the same basic shape as the original make sure to select Fixed for ‘Aspect Ratio’ in the tool options.

2. Using your mouse, click and drag to roughly the size you wish to crop, you can now fine tune the crop area by using the mouse to drag the sides of the area to their final positions. When you are happy go back to the ‘Crop’ dialog box and click OK.


Cropping to Specific Ratio

There will of course be time when you wish to use cropping to change the basic shape of your image, for instance to fit an 8 x 10 photo frame. To do this

1. From the Toolbox select the Crop tool.

2. Make sure that Fixed is selected for ‘Aspect Ratio’ in the tool options and now use your keyboard to enter “8:10” in the box. You can use the Portrait and Landscape buttons to flip the crop area if needed.

3. Using your mouse, click and drag to roughly the size you wish to crop, you can now fine tune the crop area by using the mouse to drag the sides of the area to their final positions. When you are happy go back to the ‘Crop’ dialog box and click OK.

Happy GIMPin’


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