This article is intended to know in detail about sharpening digital images. Why we need to sharpen our images and how to do it for different purposes.
Why do we need to sharpen the images?
In Photography, there are few barrications for the digital data to travel from the scene to the storage space, to remain original to the scene as close as possible. The first one being the anti-alias filter in front of the sensor, it actually reduces the sharpness of the image regardless of the quality of the lens we use while capturing(nowadays few camera sensors are already available in the market without this filter). And even the lens with highest quality, is not able to aid the capture as close as possible to the scene. All the lens come with it’s own technical limitations. The second one being the Bayer filter on the sensor which does the construction of the pixels and it’s colour details. In this process also the details gets lost and the sharpness is reduced. Sharpening to counterbalance this detail is known as ‘capture sharpening’.
Sharpening for mediums – Not all the sharpening is applicable for all display mediums, since every display has it’s own pixel density and sizes. The pixel density varies according to the way it regenerates the image from the data file depending on the display size. Mediums are not limited only with displays, it goes further with printing as well. Presently these are the two primary mediums for viewing photographs.
The other one at expert level is creative sharpening. Creative sharpening is nothing but selective sharpening. It depends a lot on what kind of image is on hand. If it is a portrait, it needs to be treated in a different way, If it is a landscape than the treatment needs to be different from portraits. A portrait needs to sharpen at eyebrows, lips and all the edges but not on the cheeks in general. To sharpen the specific areas in an image you might need to sharpen the areas selectively.
When it comes to print, again the sharpening needs to be different according to the paper and printing type. Printing type can be through inkjet, laser, offset etc., When it comes to paper it is again different, based on the type of paper and its ink absorption level. This is output sharpening.
What is sharpening anyway?
In simple words, sharpening is increasing contrast on the edges. To pick the right edges, the amount of sharpening to apply, and what radius the sharpening should be applied there from the edges, without losing any prevailing details are the tasks in our hand and there are different softwares available in the market to do the same depending upon our inputs.
In this figure, the effects of a sharpening algorithm are shown. The image and graph depict an edge transition from 40 to 60 percent. Each tick mark across the bottom of the graph represents a column of pixels. After sharpening, the transition is accentuated-darker on the dark side and lighter on the light side. This creates a halo that increases the apparent sharpness.
Image courtesy: Bruce Fraser’s Real World Photoshop.
How do we sharpen our images in Lightroom?
Photographers who use photoshop for sharpening might be using many different tools in photoshop, the well known one being ‘Unsharp Mask’. If you expect the same in Lightroom, you may be disappointed.
Engineers in Adobe have really simplified the sharpening process in Lightroom with only four controls 1. Amount – the whole amount of sharpening, 0 being nothing and 150 being the maximum amount. 2. Radius – the radius of sharpening at the pixel level. One pixel being, that one pixel will get sharpened. You can select 0.5 to 3.0 pixels. 3. Detail – Detail being the amount of detail remains to be intact while sharpening 4. Masking – This is one of the very important sub-tool in sharpening as this tool is the one which decides the area which needs to be sharpened on the image.
Screenshot of the Detail panel in Lightroom Develop module with the masking option kept on by pressing and holding alt key(option key in Mac) while dragging the masking slider.
The small preview window above the amount slider is meant for having the preview of 1:1 view of the image where the square with crosshair(marked in red colour) is placed on the image. Alternatively you can click directly on the preview window and then clicking back on the location exactly where you want to zoom in will also display the 1:1 view.
Tip : Pressing “alt” (option key in Mac) key while dragging any of the slider will provide you the distinct view of which area is getting affected by the slider.
This panel is by no means a replacement to the USM tool in photoshop, this is the Lightroom way of sharpening. This sharpening is capture sharpening.
For creative sharpening the tools available in Lightroom are Brush tool(K), Graduated filter(M) and Radial filter(Shift+M). Once you selected a tool, in the sub-menu you have to boost the sharpening option and just paint on the image where you want to sharpen specifically. You can adjust the density and flow of the brush in the tool menu itself.
If you wish to have USM sharpening tool in Lightroom, there is a plug in called Mogrify which helps us to do sharpening. Mogrify provides us very wide set of tools from sharpening, colour correction, adding borders and so many. Let us look in to it in detail in a separate post.
For output sharpening, in Lightroom there are limited options provided to the user. Only when you export your photograph you will be getting an option to adjust the sharpening for medium in the export window.
Under output sharpening in the export window, there are two primary classifications one being different type of medium as Sharpen for “Screen, Matte paper, Glossy paper” and the second being the Amount as “Low, Standard, High”. The second option remain same for all the three mediums.
Lightroom provides only limited control when it comes to output sharpening. A detailed article about sharpening in Lightroom can be found here.
This tool is not related to sharpening, though together used with sharpening shall give you very good results based on the nature of the image. This tool is a single slider works independently and is located in Basic panel itself. This tool can be used to bring out more details, if the images have lot of details in it. Let’s say like more architectural content or having more corners or lines. And this tool is a global one, if you pull this slide to your right or left it affects the whole image. If you want to use it selectively you need to use the local correction tool like Adjustment brush, Radial filter, Graduated filter as you have seen for creative sharpening.
Screenshot of clarity tool in basic panel.
Do you use any other interesting software than Lightroom and Photoshop? Did you improved your photography after learning the nuances of sharpening? I would like to know your story in the comments section!