Basic image edits with GIMP: Getting photos ready for competition requirements Dirk Pons, New Zealand March 2018. This work is made available under the Creative Commons license Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) which means you are free to Share and Adapt the material for non-commercial purposes. Introduction A degree of image manipulation is required for many photos. This tutorial explains how to use the free open source GIMP software to achieve basic edits in readiness to submit a photo to a competition. GIMP (the GNU graphical image manipulation programme) may be used for: photo editing and manipulation; graphical design; creation of original artwork. In this tutorial I only focus on the first use, which is post processing of photos. Download a free copy of GIMP. https://www.gimp.org/downloads/ The purpose of this basic tutorial is to show how to edit images for submission to a photographic competition. This covers: Rotate Crop Overall adjustments to brightness, saturation, levels Reduction (downsampling) to a required number of pixels 1
Here is my image. I took this before sunrise on the beach, and I moved the camera to follow the moving horses. This and the low shutter speed has created an interesting blur to the horses legs, and to the sea. However the horizon is not exactly level so I want to straighten that. Also I need to get it ready for submission. I am therefore going to rotate, crop, and resize this image. Flipping an image Rotation in 90deg units is via Image/Transform. I don t need to do this. Rotation For small rotations, e.g. to get a horizon level, use the fine rotation tool. Before I start, I will zoom and pan the image so that the horizon is next to the edge ruler that way I have a horizontal gauge to compare against. Zoom is shift middle mouse wheel. Pan is middle mouse wheel, or the scroll bar. Then rotate with Shift R or Tools/Transform Tools/Rotate or pick the item on the graphical toolbox. 2
Left mouse down and drag the image around to rotate it. Or type in a degree value. Image: I am rotating the image around the centre point, using the mouse. This image only needs less than a degree of adjustment. Possibly I did not need to bother, but it is done now. When done, press ROTATE to execute. Zoom back out when done. After rotation it will be necessary to crop the image. Crop Use one of these: Shift C Tools\ Transform Tools\ Crop or pick the item on the graphical toolbox. Then click on the image and draw a rectangle defining the area to retain. This rectangle can be an arbitrary size, or you can fix the aspect ratio. If you want a specific ratio, such as the commonly used 3:2 ratio used in competitions, then enter this into the tool options. This is what I have done. You can zoom into the corners to check that your rectangle is over the image. 3
Cropping an image that has previously been rotated. The same applies if you simply want to crop the image to concentrate on a smaller area. (1) Activate the crop tool. (2) Option - Select fixed ratio and (3) enter a value. (4) Left click with mouse on one corner of image. (5) Drag rectangle to other corner, let go mouse. Then do fine adjustments by dragging the corner squares. Finally press ENTER to commit or ESC to abandon. There is no on-screen button to press, instead you must Press ENTER on the keyboard to execute the crop (or ESC to escape.) Change colours Now would be a good time to do any colour adjustments. The ones shown here apply to the whole image. For localised edits you would need to use masks. There are multiple options at this point. They can all be found off the Colours menu. Colour balance This adjusts the primary colour levels. There is a simple slider for each of the three primary colours. 4
I decide not to accept this change, so I cancel and move on. Hue-saturation The hue will change the colour cast. I find this less useful, except for creative idea. There is also lightness and saturation to experiment with. My image is a bit grey, so turning up the saturation will make it more colourful. 5
Colorise This changes the hue. Well for some situations this would be useful, but today is not one of those. I cancel this idea. 6
Brightness and contrast This is good adjustment to consider. In this case the benefits are not quite worthwhile to my thinking. 7
Levels Adjust colour levels This refers to how the darker and lighter regions are represented in the image. These can be done with manual control or by dragging the curve to a new shape. Click on the curve to add new control points, and then drag these around. With this I could, for example, make the brown coats of the horses more apparent as shown below. This has also made the rider details more visible. Hmm I am tempted. On the other hand I want the viewer to get the same sense of speed that originally made me appreciate the scene. I think this change causes the eye to look at the people instead of the speeding horses. So I decide against the adjustment. Every photo is different, and also each photographer has their own style. You will have to apply your own judgement. In the end I decide to only make one small colour change, which is to increase saturation (+20). My reason is as follows. It was a photo taken in difficult low-light conditions (105mm, f/5.6, 1/10s, ISO3200) and hand-held. My image is quite grainy, though it may not look that way. Many of the above colour changes make the graininess more apparent in this image, and I think that would be distracting. I guess someone who really knows their colour manipulation stuff would be able to improve the image, but this would take a lot of time for me. So in this case I am going to go with the colours as the camera caught them, with a small boost to saturation. In a different case I would use some of these colour adjustments. 8
Now that I ve check the colour options, and made my decision, it s time to reduce the photo down to competition specifications. I take a moment to save the image first. With GIMP this means exporting a jpg, and optionally saving the GIMP file. See saving instructions at end. Reduce image pixel size Competition entries may require a reduced pixel size for the image, e.g. 1620x1080 pixels. First crop your image to 3:2 ratio per above, if practical. Then scale the image down. USE THIS: Image / Scale image Other methods: Shift T or pick the item on the graphical toolbox. Unfortunately each of these methods results in a different user menu, which is confusing. The best for my purpose is Image / Scale image. This gives me the level of control I need. See image below for instructions. Scale an image: Menu Image / Scale image. Then (1) click the locked chain to preserve the aspect ratio. (2) Type the desired width, which is 1620 pixels in this case. Press TAB. (2) Check the height. If you cropped the image correctly it should automatically be 1080 pixels. You could unlock the chain and type in 1080 but this will stretch your image. Otherwise keep it 9
locked and make adjustments to width or height such that both are within the competition requirements. (4) Press screen button to complete. Export to a new file name. Save file Save your modified photo to jpg. Use File/Export as. Do not over-write your old file. Instead give a new name to the exported file. I have put RotCrSmall behind the original file name to remind myself that this file has been rotated, cropped, and reduced in size. This is the JPEG file that you will submit to the competition. You can also save the xcf file. This is useful if you want to make further edits in the future. However this is of no use to the competition. Here is my finished result. The horizon is nice and straight, the colours slightly boosted, and the image is the small size needed for submission. The colour change is mild so you might not see much change in that area. The reduction in pixels has not materially changed the character of the image, so that is good too. GIMP is a powerful image manipulation software tool, and it is straight forward to do all of the standard preparation for a competition submission. The software has other more complex features for the more demanding user. For more tutorials on GIMP, including advanced features: https://www.gimp.org/tutorials/ 10