Home » Learn » How to Sharpen an Image in GIMP
How to insert an image in GIMP
By Tomas Boldt | Updated on May 31, 2021
Sharpness can be the difference between a great photo and a great one, making it an essential step in any photo editing workflow. GIMP only has a couple of sharpening options, but it’s important to use them correctly to get perfect, sharp images that don’t look over-processed.
There are two main ways to sharpen an image in GIMP and both are easy to use. You can focus exclusively on selected areas using a brush-based tool, or you can focus the entire image at once with a filter.
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Method 1 : Select the Sharpen tool from the toolbox and hand-paint the areas that are in focus.
Method 2 : Open the Filters menu , select the Enhance submenu and click Sharpen (Unsharp Mask).
Si bien el afilado es fácil de aplicar, es aún más fácil aplicar demasiado. Probablemente haya visto imágenes exageradamente nítidas en línea sin darse cuenta de por qué se ven tan mal, pero un poco de atención a los detalles (y esta guía) se asegurará de que eso nunca le suceda a ninguna de sus imágenes.
Echemos un vistazo más de cerca a estos dos métodos para enfocar una imagen en GIMP, aprenda cómo funcionan y dónde encajan mejor en su flujo de trabajo. ¡Sigue leyendo para obtener más consejos de afilado!
- Method 1: The Sharpen Tool in GIMP
- When to Use The Sharpen Tool
- Method 2: Sharpening an Image with a GIMP Filter
- When to Use the Sharpen Filter
- Sharpening with GIMP Plugins
Método 1: la herramienta Sharpen en GIMP
Usar la herramienta Enfocar es tan fácil como usar cualquiera de las herramientas basadas en pinceles de GIMP, aunque no es inmediatamente obvio dónde encontrarla en la caja de herramientas. Blur y Sharpen son dos caras de la misma moneda, y GIMP los agrupa bajo el ícono de lágrima en la caja de herramientas.
También hay otras dos herramientas incluidas en este lugar en la caja de herramientas de forma predeterminada (aunque no estoy seguro de por qué exactamente), por lo que si no puede encontrar la herramienta Desenfocar / Enfocar, puede estar detrás de los íconos Difuminar o Esquivar / Grabar en cambio. Usar el atajo Shift + U siempre es una forma más rápida de comenzar a enfocar.
Like all brush-based tools in GIMP, there are a number of options that can affect how the sharpening is applied from Opacity to Force, but Rate is the most important. If you’re going to use the Sharpen tool, use a mid-range Rate setting and gradually build up the effect as needed.
The Sharpen tool gives you the ultimate degree of control over how sharpening is applied to your image, but that great power comes with a few downsides that limit its usefulness.
Every click restarts the sharpening effect, so you often have to work in very long strokes that limit your undo options. Additionally, there’s no mask or guide that shows you exactly where you’ve already applied the tool, so you can wind up with very inconsistent results if you’re not careful.
When to Use The Sharpen Tool
Because of these issues, the Sharpen tool works best when you use it with a light touch. If you want to sharpen your model’s eyelashes a bit or you want the bumblebee’s fuzz in your macro shot to really pop from the background, the Sharpen tool works well – but not for much more.
If you find yourself using the brush over more than just a small section of your image, you’re probably better off applying a Sharpen filter to the entire image – so let’s take a look at how that works.
Method 2: Sharpening an Image with a GIMP Filter
If you were having trouble finding the right Sharpen filter to use on the whole image, you’re not alone. You can find the correct tool by opening the Filters menu, selecting the Enhance submenu, and then clicking Sharpen (Unsharp Mask). Yes, Unsharp Mask is the right one!
The name is confusing enough that GIMP’s developers put a bit of an explanation in the tooltip popup for the Sharpen (Unsharp Mask) filter
This slightly confusing name dates back to a technique created for darkroom film development, where a blurred positive version of a photograph is used to enhance the negative film copy of the image you’re working on. Somehow.
If that doesn’t make sense to you at all, don’t worry – I don’t understand exactly how it works either. The good news is that you don’t have to understand why it works in order to use it effectively (though you can read about unsharp masking if you’re curious.)
The Sharpen filter uses a digital version of the unsharp masking technique, so extra credit if you have a basic understanding of unsharp masking. However, you only need to focus on 3 settings to control your sharpening result: Radius, Amount, and Threshold.
Sharpening works by detecting edge lines in your image – essentially, the separation of different objects – and increasing the relative contrast of the pixels near those edges. Keep that in mind as you think about the three settings and their effects.
1. Radius – pixels within the set radius of any detected edges receive sharpening
2. Amount – how much sharpening is applied to the pixels within the radius
3. Threshold – sets the contrast difference required for GIMP to detects an edge
It’s handy to use the Preview toggle to compare the ‘before and after’ of your sharpening effect, and you can also use the Split view toggle to see half your image ‘before’ and half of it ‘after’. Split view doesn’t always help, though, depending on the exact content of your image.
When to Use the Sharpen Filter
Knowing when to use the Sharpen filter is the most important part of using it successfully – and I don’t mean knowing if you should use it, because I have yet to see a photo come out of a camera without needing some sharpening.
Sharpening should always be the very last step in your image editing workflow, after all your edits and any final image size adjustments are made, especially size reduction. Otherwise, you’re going to wind up messing with the effect and having to do it all over again.
Sharpening with GIMP Plugins
Many photographers and image editors are extremely… precise (read: obsessive) about how sharpening is applied to their image. As a result, many different plugins exist with different sharpening methods, algorithms, and endless configurable adjustments.
The eagle-eyed readers among you might have noticed in my screenshots that I have a few different sharpening options available, thanks to a few of the GIMP plugins I have installed.
Resynthesizer and GMIC each have their own sharpening options, and you can read more about them in the best GIMP Plugins article. You don’t need to use them if you’re not curious, because GIMP’s Sharpen filter already does a great job!
About Thomas Boldt
Je travaille avec des images numériques depuis l’an 2000 environ, lorsque j’ai eu mon premier appareil photo numérique. J’ai essayé de nombreux programmes d’édition d’images. GIMP est un logiciel gratuit et puissant, mais pas exactement convivial jusqu’à ce que vous soyez à l’aise avec lui, et je voulais vous faciliter le processus d’apprentissage ici.
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How to Change Image Resolution Using GIMP
Image editing programs like GIMP (GNU Image Manipulation Program) can give you resolution information and allow you to change the resolution of an image. One would change the resolution of an image particularly for printing purposes, because the quality of the print is dependent on the resolution of the image.
1. With GIMP open, go to File > Open and select an image
Tip: You may right-click and save the tiger image below to use it as a practice image.
2. Go to Image > Print Size
3. A Set Image Print Resolution dialog box will appear like the one pictured below.
If Print Size Width and Heights are not shown as inches, select the dropdown beside Height and select “in”.
4. In the X and Y Resolution fields, type in your desired resolution.
You will notice that when you type a value into the Resolution field, the values of the document’s width and height also change. This is because GIMP is changing only the resolution of the image and not adding any additional pixels (which is what happens when an image is resized). To change resolution we are NOT changing the number of pixels in the photo, but changing only how many of those pixels will be displayed per inch.
5. Click OK to accept the changes.
Congratulations! You have successfully changed the resolution of an image!
In this example, we had an image with a 300ppi resolution. I wanted to print this image in a professional publication and the image needed to be at least 600ppi.
Remember that the number of pixels in the image have stayed the same because we did not add or subtract any pixels to the image, only determined how many of those pixels to display per inch.
However, note that the Width and Height decreased by half when the Resolutions doubled. This means that in order to print at 600ppi and retain full-quality, I can print this image only as large as 5″ x 3.33″.
What happens if we decrease our resolution?
As you may have guessed, our Width and Height doubled when we halved our Resolutions. Now my image will print larger, but the quality will be much lower.
What does it all mean?
It’s a game of give and take!
We notice that the pixel dimensions never change. We started with an image at 3000 x 2000 pixels (px) and ended with the dimensions still being 3000 x 2000px. This is important to remember, because when we change resolution we are changing only how many pixels will be displayed per inch of the image, not how many pixels make up the image. Since we are not adding or subtracting any information (pixels) from our image, our image has to always balance out to its original 3000 x 2000 px. If we increase resolution then we must decrease from somewhere! Since the pixel dimensions cannot change, the only other place to decrease is our document size (width and height of image).
Here’s the math to make it more clear: Sample Image is 3000 x 2000 px
600ppi: 3000 pixels / 600 pixels per inch = 5 inches
2000 pixels / 600 pixels per inch = 3.33 inches
300ppi : 3000 pixels / 300 pixels per inch = 10 inches
2000 pixels/300 pixels per inch = 6667 inches 150ppi : 3000 pixels/150 pixels per inch = 20 inches
2000 pixels / 150 pixels per inch = 13.33 inches
72ppi : 3000 pixels / 72 pixels per inch = 41.67 inches
2000 pixels / 72 pixels per inch = 27.78 inches
How does resolution affect printing?
In this example, our image was sent to print from a laser printer on standard 8.5 x 11 sheets of paper.
72 dpi : The document size is so large that it does not fit on an 8.5 x 11 sheet and is cropped. The quality of impression is extremely low, leaving the image very blurry or “soft”.
150 dpi – The document size is still too large for the 8.5 x 11 sheet and the quality is mediocre, making the image look acceptable, but not very desirable.
300 dpi: the image when using the sheet of paper and the quality of the print are muy buena, with nítidos y nítidos details.
600ppi: The image is significantly smaller than the other files, but the quality is extremely high.
Which to choose? The 72ppi and 150ppi images are too low in quality to produce a high-quality print, so they are discarded. The 300ppi and 600ppi images looked very sharp, but the 600ppi image was too small. For this example, the 300 dpi image would work best due to its larger print size and high quality.
The key to printing images is finding the best resolution that will produce both the size and quality you need.