|by Fang Sher Chyet|
For most people that just switched from Compact Digital to DSLR, first few comments will be the images from camera LCD of DSLR are not as sharp as those from compact camera. In my opinion, there are 2 main reasons:
|So the question that you might ask is why DSLR does not do in-camera sharpening? Most camera manufacturers figure that most Compact camera users will not bother with post processing, hence sharpening for compact camera is done automatically in-camera. However, for DSLR, it will let photographers have total control of settings and post processing.|
The other point to note is most digital cameras have an anti-aliasing filter in front of its sensor; the purpose of the filter is to reduce artifacts that may present itself in the photo. However, this filter also caused the photo to be blurred slightly and that means that images straight from digital camera is slightly soft and require some amount of sharpening.
|What is Sharpening?|
|Our eyes see things with well-defined edges as in focus. Hence sharpening a photo essentially is to enhance the edge of the subject by exaggerating neighboring light and dark pixels. Sharpening filters in Photoshop or other post processing software do is to detect transitions (edges) and make them more obvious. Here is a closer look at what these sharpening filters do:|
|As you can see, the sharpening tool is making the dark side of edges darker and the light side of edges lighter in order to enhance the edge to give viewers a better-defined edge.|
|When do you perform sharpening?|
|Sharpening is usually the last step in your post processing workflow. It is usually done after you resize the photo for the intended output (for printing, web, or for digital displays, etc). In general, the later in a workflow that the sharpening is performed the better it will be. Since image editing can degrade the sharpness of an image, sharpening performed early in the workflow will likely be degraded by subsequent editing.|
|What are the common Sharpening Techniques in Photoshop?|
| There are many different ways to sharpen a photo, however, I will only cover the following 3:|
|Unsharp Mask (USM)|
|This is probably the most commonly used sharpening technique by most photographers. The name came from sharpening techniques used in the darkroom era.|
|There are 3 settings in Unsharp Mask (USM):|
AMOUNT – determines the amount or aggressiveness of the “sharpening” action. What you should see is that as the AMOUNT increased, the colors of the neighboring edges get more exaggerated. In other words, the edge line at the lighter side gets lighter with each increase, the edge line on the darker side gets darker.
RADIUS – determines how far or wide the edge line will turn lighter or darker. A low radius means that the sharpening will be applied right next to the edge only. A larger radius applies the sharpening further out from the edge.
THRESHOLD – determines how much tonal difference must exist between two adjacent pixels before any change is applied. A setting of 0 means that almost any tonal difference will be sharpened. A setting of 2 means that sharpening will be applied only when neighboring pixels have a tonal difference of 2 levels or more.
|Normally, for web posting at NPSS or 800px X 533px, my USM setting is as follow:|
Amount – 150 to 250 (My default is 200)
Of course, depending on situation, you can adjust Amount and Radius accordingly. When using USM in Photoshop, do turn on the Preview (have a tick mark next to Preview). This will help you in deciding the optimum amount of sharpening required.
For prints and/or larger web display, you can be a little more aggressive in the amount and radius.
USM is popular and easy to use, but it has its limitations. For example, using USM sharpening, other than the adjustment of amount, radius, and threshold there is no flexibility to adjust the sharpening to the specific needs of a particular image.
Starting from CS2, Photoshop comes with a new sharpening filter – Smart Sharpen. Similar to USM, Smart Sharpen has Amount and Radius to control the level of sharpen required in a photograph. There are 2 main advantages of Smart Sharpen over USM. First is the introduction of Remove option. It allows you to remove 1 of 3 blurring options (Gaussian, Lens and Motion). The other advantages is the introduction of sharpening for Highlight and Shadow. One of the “side effect” of USM is noise, the control of shadow and highlight in Smart Sharpen minimize the noise problem as seen in USM, as it allows the photographer to set different amounts of sharpening for the mid-tone, highlight, and shadow areas.
Smart Sharpen Menu (Advance Options)
Smart Sharpen (Shadow tab)
Smart Sharpen (Highlight tab)
|When using Smart Sharpen, select the Advanced option (as shown above). There are 3 tabs under the Advance Option – Sharpen, Shadow and Highlight. Under Sharpen, You will need to enter the Amount and Radius. The settings for both parameters will be the same as those suggested value in USM.|
Normally, for web posting or 800px X 533px, my setting is as follow:
Amount – 150 to 250 (My default is 200)
These settings are essentially to sharpen the mid-tones of your photo.
|Smart Sharpen – Shadow Tab|
For the Shadow tab, this is to let the Smart Sharpen filter know the different amount of sharpen for the shadow area. Noise is more commonly found in the shadows areas of an image, hence, I will usually tone down the amount of sharpening in the shadow areas to reduce noise problem.
There are 3 settings in Shadow tab:
Fade Amount – determines how much the sharpening is “faded” or reduced. The higher the setting, the lesser the amount of sharpening is applied. A setting of 0 will result in no reduction of sharpening. A setting of 100% will result in no sharpening of the shadow.
Tonal Width – determines which tonal values will be affected by the reduction in sharpness. Smaller values of Tonal Width result in only the lightest shadows being affected by the sharpening reduction. Larger values of Tonal Width will result in a wider range of the shadows being affected.
Radius – determines how far or wide around a particular pixel will be evaluated to determine to which tonal area that pixel belongs
My normal setting for Shadow tab is as follow:
Fade Amount – 70 to 90
Smart Sharpen – Highlight Tab
Similar to Shadow Tab, There are 3 settings. The application is the same as Shadow, and my normal setting is:
Fade Amount – 20 to 40
|High Pass Filter|
I learnt about this technique not too long ago. It is not like USM or Smart Sharpen that are available from the pull down Filter menu. It involves a few steps by using duplicate layers. It is a bit more complicated than USM and Smart Sharpen, but not by that much.
Using USM and to lesser extend Smart sharpen, we essentially sharpen the whole image. For High Pass Filter, any areas in the image which are not an edge are left untouched. The only areas that have sharpening applied to them are the edges, which is exactly what we need when we try to sharpen the photo.
The other advantage of using High Pass Filter is that sharpening is done on different layers. Hence, sharpening can be changed or undone later by just delete the High Pass Filter. For USM and Smart Sharpening, you will not be able to do that.
There are total 5 steps to achieve sharpening using High Pass Filter:
|Step 1 : Duplicating Layer|
As indicated above, High Pass Filter is done on separate layer, you will need to duplicate a copy of the Background layer. To duplicate a layer, use ctl-J (Windows) or cmd-J (in Mac):
Step 2 : Change the Blending Mode
As we only want the High Pass Filter to sharpen the edges, we need to turn all non-edge areas of the image into neutral gray, and the Overlay blend mode leaves all neutral gray areas alone, which means no sharpening will be applied to any of those areas
|Step 3 : Apply High Pass Filter|
First, choose from the pull down menu of Filter, follow by Other and High Pass Filter:
There is a slider bar at the bottom of High Pass Filter to adjust the intensity of the filter, click the “Preview” checkbox in the top right corner to view the effect while you vary the intensity of High Pass Filter. As you drag towards the right, you’ll be adding more sharpening, and as you drag to the left, you’ll be reducing the amount of sharpening.
I recommend you to start off with a very low radius value, somewhere between 0.5-3 pixels, depending on the pixel size of your image. In this example I am using a small image (800x533px) so I use 0.8 pixel. If you go too high, you’ll begin to see a halo effect around the edges of your image, and you want to avoid that, so back off on the radius value by dragging the slider bar to the left once the halos begin to appear.
After clicking “OK”, if you are satisfied with the sharpening, you are done and go to Step 5. If you want to fine tune the sharpening, follow Step 4.
|Step 4 : Change Blending mode to Hard Light or Soft Light |
If further adjustment on sharpening is required, you can either change the blending mode to “Hard Light” (to increase sharpening) or “Soft Light” (to decrease sharpening). You can also making use of the opacity level to further fine tune the sharpening.
Step 5 : Flatten the layers
To flatten the image, you will need to select the “Layer” from the pull down menu and select “Flatten image” and you are all done.
If an image has no noise issue, the quick and dirty way is to use USM and be done with it. However, to have quality sharpening done on you photo, I will recommend either Smart Sharpen or High Pass Filter.
Using Smart Sharpen is a one step process but to get a more accurate shar pening with minimal impact to the overall image, High Pass Filter will be my choice particularly if there is potential noise issue in the photo.