This tutorial will take you on a step-by-step tour of how I sharpen an image with GIMP. GIMP has two advantages: it's free and it runs on Linux. This tutorial assumes you have already gotten rid of dust spots, rotated and cropped the image, adjusted the contrast and added a bit of saturation. This part is almost identical to photoshop. The hardest part (at least for me) is the sharpening. A very important side-note: Photoshop and GIMP use completely different measurements for sharpening. Sharpening an image with radius 0.3, amount 0.5 in GIMP is different to sharpening the image wih radius 0.3 and amount 50% in Photoshop!
text refers to where something can be found in the menu, for example: File, Quit
to exit. Here is the image I will use, an Emirates Boeing 777-200ER with registration A6-EMH taken in Geneva.Rotated, cropped, levels and saturation OK, now for the sharpening. Please note: image is not resized yet!Add Alpha Channel
: Layer, Transparency, Add Alpha Channel
or right-click on the layer (on the right, called "Background"), Add Alpha Channel. Now, if you use the eraser tool the image will become transparent and not white. This will be important later. Duplicate Layer
: Layer, Duplicate Layer
. We will sharpen the upper layer and leave the lower layer unsharpened.Sharpen
: Filters, Enhance, Unsharp Mask
. I'm guessing this depends very much on your camera and lens, with my D90 and 70-300mm lens I use 0.3 for the radius (my lens is fairly soft in comparison to the more expensive lenses), 0.5 for the amount (this varies from picture to picture) and 4 for threshold.First round of sharpening: you can see "BOEING 777-200" in the preview is already a lot sharper!Resize
: Image, Scale Image
. Now (and only now!) do we want to get our image into an acceptable format with a width of 1000-1600 pixels. If resizing causes jaggies, there are two options: either opting for larger dimensions (say a width of 1600 pixels rather than 1024), or resizing the picture in several steps (3341 --> 2200 --> 1600 --> 1024 for example). I almost never have this "problem" as my lens isn't sharp enough, so I will resize this in one stop here.Sharpen
: Because we resized the picture, it needs a last touch of sharpening. This time, I use the following settings:
Radius: 0.1 (the lowest possible)
Amount: 0.5 (again, this varies strongly from picture to picture
Threshold: 4Remove Jaggies
: Jaggies are areas in the image, usually edges of objects, for which the sharpening was too strong. To make the image perfect, we need to "unsharpen" them, we will do this with the eraser. So, we click on the eraser tool in the toolbox or press Shift+E and set opacity to 30%, Brush to the large 21x21 Circle and Scale to 1. Now, because we have a completely unsharpened layer underneath (but otherwise exactly identical), we can just rub out the jaggies. These can be found here:
- -Titles, especially the top of the E and m and the "www.emirates.com".
- -Other "painted stuff" on the aircraft, in this case the "BOEING 777-200" underneath the cockpit, the registration and the black and red parts of the flag on the tail.
- -Any sharp edges, especially the wings and bay doors above the undercarriage.
- -Top left of the engine.
- -The cable in the background may not have jaggies, but it surely will look better unsharpened, so I will set the eraser to opacity 100% to rub it out completely. Likewise, the image looks better when the sticks in the ground are not so aggressively sharpened.
Some other common places where jaggies occur frequently (but not found on this image)
- -The edges of the plane, especially the nose and rear.
- -Cockpit windows.
- -Technically maybe not jaggies, but sometimes the background looks better unsharpened, especially when it was never in focus anyway.
To unsharpen the sky: use the magic wand tool, click in the sky a few times holding shift until the whole sky is selected, then press delete.Success, a beautiful image of an Emirates 777 For comparison: the same image with the jaggies. The difference may be subtle, but it is noticeable!A very ugly image showing where the jaggies were erased
Last: some helpful shortcuts I use.F4
: Add alpha channelF8
: Duplicate layerF9
So once the image is ready for sharpening, all I have to do is hammer F7 F8 F9 and enter the correct values. Saves me a seconds so I thought I'd share
I hope this tutorial helps your postprocessing!