Many people mistakenly believe that unsharp masking (USM) is a new technique specific to digital imaging, which is not the case--it is an image manipulation technique that has been around since the 1930s. It is a way to increase the sharpness of an image, which confuses some people because of its name. The original film technique required the use of a slightly out-of-focus positive image as a mask. When the negative and positive were registered together and exposed to a new negative, they actually caused an illusion of increased sharpness. This process has been refined in digital photography and uses a Gaussian blur as the unsharp mask. Read on to learn how to use this process with GIMP (although the process is really the same with most imaging editing programs).
Instructions
- 1
Start GIMP and open your image. Try and find an image that needs to be a little sharper. Unsharp masking is different than sharpening, which is another algorithm that simply adjusts the edges of all pixels. With unsharp masking you can control the amount of sharpening more without adding artifacts through the entire image. Click on FILTERS/ENHANCE to find and open the USM toolbox.
2Once the toolbox is open, remember to enlarge the preview screen to work on your image. The first thing I do is to adjust the THRESHOLD. This is counter-intuitive to the way the toolbox is laid out since it is the last adjustment slider in the toolbox. Threshold controls the minimum highlight value that will be sharpened. The threshold setting can be used to sharpen hard edges without impacting softer edges. Higher threshold values limit areas of low contrast and give you more control over the other settings.
3Adjust the AMOUNT slider after adjusting the threshold. This controls how much darker the edge will become after the mask is applied. It really controls how much CONTRAST each edge pixel will have. This single control is similar to the SHARPENING filter in GIMP.
4Adjust the RADIUS. You need to be careful when choosing a RADIUS since high values will impact the quality of the image more then any other control. This is why I adjust RADIUS last. Too large a radius adjustment will result in artifacts and may cause halos in the highlights.
5Click OK when you are all done and the final image will be rendered. First, the GAUSSIAN CURVE will be created and applied, the new values will be interpolated and then the image rendered in the same screen. Remember to save your final image under a new name. The difference should be slight, not dramatic. Notice the dog stands out more, the trees are sharper and you can now make out the sign in this image. Using unsharp masking requires patience and experimentation, but it can dramatically add value to an image.
Many people mistakenly believe that unsharp masking (USM) is a new technique specific to digital imaging, which is not the case--it is an image manipulation technique that has been around since the 1930s. It is a way to increase the sharpness of an image, which confuses some people because of its name. The original film technique required the use of a slightly out-of-focus positive image as a mask. When the negative and positive were registered together and exposed to a new negative, they actually caused an illusion of increased sharpness. This process has been refined in digital photography and uses a Gaussian blur as the unsharp mask. Read on to learn how to use this process with GIMP (although the process is really the same with most imaging editing programs).
Instructions
- 1
Start GIMP and open your image. Try and find an image that needs to be a little sharper. Unsharp masking is different than sharpening, which is another algorithm that simply adjusts the edges of all pixels. With unsharp masking you can control the amount of sharpening more without adding artifacts through the entire image. Click on FILTERS/ENHANCE to find and open the USM toolbox.
2Once the toolbox is open, remember to enlarge the preview screen to work on your image. The first thing I do is to adjust the THRESHOLD. This is counter-intuitive to the way the toolbox is laid out since it is the last adjustment slider in the toolbox. Threshold controls the minimum highlight value that will be sharpened. The threshold setting can be used to sharpen hard edges without impacting softer edges. Higher threshold values limit areas of low contrast and give you more control over the other settings.
3Adjust the AMOUNT slider after adjusting the threshold. This controls how much darker the edge will become after the mask is applied. It really controls how much CONTRAST each edge pixel will have. This single control is similar to the SHARPENING filter in GIMP.
4Adjust the RADIUS. You need to be careful when choosing a RADIUS since high values will impact the quality of the image more then any other control. This is why I adjust RADIUS last. Too large a radius adjustment will result in artifacts and may cause halos in the highlights.
5Click OK when you are all done and the final image will be rendered. First, the GAUSSIAN CURVE will be created and applied, the new values will be interpolated and then the image rendered in the same screen. Remember to save your final image under a new name.
Enhance your photography skill,The Top Secret Photography Techniques
. The difference should be slight, not dramatic. Notice the dog stands out more, the trees are sharper and you can now make out the sign in this image. Using unsharp masking requires patience and experimentation, but it can dramatically add value to an image.DIY Instructables - Share What You Make
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