Digital Image Sharpening

What is Sharpening
As we had previously discussed, when we take a digital picture, we are capturing light photons and recording them on an image sensor in the form of pixels. It takes millions of pixels (similar to a mosaic) that allows our mind to combine these pixels and thus see patterns and shapes which create our image. Sharpening is the process where we enhance the contrast between these pixels so as to create the visual perception of a sharper and more realistic image. 

Sharpening does not actually make an image sharper but rather it increases the contrast between light and dark pixels along the edges. It does this by comparing adjacent pixels and determines their differences in brightness or contrast values. When it finds a difference, it determines there’s an edge. Sharpening makes darker pixels slightly darker and lighter pixels slightly lighter. The end result is the edges between these darker and lighter pixels become slightly more pronounced. The more Sharpening that is applied, the more pronounced these edges become.

Why Sharpen
When viewing an image our eyes are usually drawn to the brightest and sharpest areas in the image. Thus, when we sharpen a subject in our image; our eyes are drawn to that subject. A sharp subject that is perceived as clear, with texture and details, also is perceived as more lifelike. Sharping can help make our images more interesting and compelling to look at. 

When is Sharpening Needed
If you’re shooting using a JPEG file format you almost never need to sharpen your image as the process of creating the JPEG picture includes some degree of automatic Sharpening. If you are shooting using a RAW file format, you should almost always perform some degree of Sharpening as this format typically contains lots of image data but leaves the pixels in an unprocessed, flat, un-sharpened state. 

Exceptions to these guidelines may be when you wish to further sharpen your JPG image and/or when you may wish to leave your RAW image (or parts of it) with a “soft” effect. 

Where & What To Sharpen:
When viewing the world around us, our minds typically perceive most objects and scenes as being sharp. Objects that are closer will seem sharper with more details and texture defining the subject. Objects that are farther away or of similar light and color will (to some degree) blend and thus be perceived as “softer”. 

When Sharpening an image in post processing, most people will Sharpen the entire image at once (in essence doing Global Sharpening). This may not however create a realistic scene as our eyes and mind perceive it. 

A more realistic way to sharpen our image would be to do so selectively. By sharpening only our subject(s) and it’s supporting elements, you can direct the viewers eyes to the area of the image you have determined is most important. 

When & How to Sharpen

Using Photoshop there are many different methods how an image can be sharpened. Ultimately the process of what type and how much to sharpen is a matter of individual taste and thus is more of an Art then a Science. That being said, not enough sharpening may leave your image dull and unrealistic while too much sharpening might cause “pixelization” where the image itself breaks down into a puzzle of dots. 

When I first started learning how to edit my digital images, I was told to only sharpen at the very end of my workflow, just before printing. The reasoning behind this is that sharpening modifies the pixel information and if I was going to do additional adjustments (to these pixels) I should do so with the pixels in an un-altered state. This is no longer the case as the techniques and tools available for sharpening nowadays have been greatly enhanced. 

To get the most out of your images, Sharpening can and should be done at several different stages (as long as it is done carefully and with knowledge of what effect Sharpening is having in the image). As such, sharpening is now best done during Capture, Pre-Image Processing (of Raw Files), Image Processing (known as Creative) and Output.

1)    Focus, DOF And Its Effect on Creating Sharp Images During Image Capture
When we take an image with our camera; we choose the ISO; Shutter Speed, and Aperture (f-stop) as well as the Focus Point(s). These decisions determine what subjects in our image are sharp and to what degree DOF (Depth Of Field) and Motion Blur may or may not affect our composition. 

Using a low f-stop (such as f/2.8) would allow us to bring our subject into sharp focus while blurring the background. Using a higher f-stop (such as f/16) would increase our DOF and allow us to retain sharpness throughout most of our image. Likewise, using a low/slow shutter speed (lasting several seconds or longer) would blur moving objects and light while using a high/fast shutter speed (lasting fractions of a second) would “freeze” moving objects so they become sharp, clear and detailed. Neither method and setting is right or wrong; it’s more a matter of what is your subject and what you are trying to achieve. 

2)    Sharpening During Pre-Processing (also known as Deconvolution Sharpening or Capture Sharpening) 

Deconvolution Sharpening is designed to compensate for and correct the inherent “softness” created by our camera and lens during “Image Capture”. This “softness” is typically created by our camera’s technology limitations such as the use of poor-quality cameras and lens or in higher quality camera’s “low-pass, anti-alias” filters. Image “softness” is also part of the “unprocessed nature” of image capture using the RAW file format.

Guidelines For How To Do Deconvolution Sharpening:
i)    When using ACR (Abode Camera Raw), access the Details tab. 

ii)    Zoom in and expand your view (ie; 100%)

iii)    Set the Radius Slider all the way to the left (to .50) and the Detail Slider all the way to the right (to 100).

iv)    You can now move the Amount Slider to the left or right to get the amount of sharpening you desire (typically somewhere between 30 and 50).

v)    To use the Mask Slider, decrease your Zoom (ie; fit in Window) press the ALT Key (or OPT key on a MAC) while moving this slider to the left or right so you can see what areas are being sharpened or not (when you do this, the image will temporarily turn black & white with the white areas being affected by the sharpening and the dark areas, not). 

vi)    Below the Sharpening Sliders are adjustments for reducing Noise. Noise Reduction is and can be a complex subject and although it affects an image's sharpness, is an entirely different topic. As such, it needs to be addressed at a future time.

3)    Sharpening During Image Processing (Creative Sharpening)
Photoshop has several different tools for sharpening. Some of these represent technologies developed over different periods of time while other may be useful in different situations. Presented below are some of these different tools and techniques (not represented in any order of priority): 

i)    The Sharpen Tool 
The Sharpen tool is a brush that can be used to selectively sharpen small areas or objects within your image (ie; a person’s eyes or the stigma of a flower, etc). As a brush, you have the ability of selecting its shape, strength and Layer Opacity as well as the ability to add a Layer Mask. 

When you use the Sharpening Tool to paint over an object in your image, this brush will increase the pixel contrasts only in this brushed specific area. The more you paint over this area, the more pixel contrast will be created. 

Great care should be taken when using this tool as it has a tendency of increasing Noise. To overcome this problem, later versions of Photoshop include a new “Protect Detail” feature that allows you to set the brush’s sensitivity. Also, when used directly on a Pixel Layer, it works in a destructive manner, thus you will want to Sharpen on a separate layer.
 

Guidelines For How To Use The Sharpening Tool:
(1)    Create a new layer above your Pixel layer. Rename this layer “Sharpen Tool”. This will allow you to Sharpen in a non-destructive manner.

(2)    Zoom in and expand your view (ie; 100%)

(3)    Select the Sharpen Tool and set as follows:
(i)    Select your desired Brush

(ii)    Set the Amount to a low value (maybe around 15 to 25 or so)

(iii)    Turn on the “Sample All Layers” and “Protect Details”

(iv)    Begin to “paint” the area you want sharpened

b)    Filter --> Sharpen -->  Sharpen 

The Sharpen Filter can be used for quick and easy sharpening but has very limited capabilities. This Filter will apply a small amount of Sharpening to a Pixel Layer (how much Sharpening is not known as finding any information about this Filter is extremely difficult). As there are much better Photoshop Tools available for Sharpening, I usually do not recommend using this as there are no Adjustment Sliders for you to control its effect. That being said, this Filter works fairly well and can be used when you need a fast and simple method to sharpen an image. You can also use a Selection with this Filter to selectively Sharpen an area or object within your image. 

Guidelines For Using The Sharpen Filter:
(1)    Create a new layer above your Pixel layer. Rename this layer “Sharpen Filter”. This will allow you to Sharpen in a non-destructive manner.

(2)    Zoom in and expand your view (ie; 100%)

(3)    Select the Filter Menu

(4)    Select the Sharpen Menu 

(5)    Select Sharpen (there are no Adjustment Sliders to use with this tool). Using the Selection Tool, you can select an area or object within your image

c)    Filter --> Sharpen --> Sharpen Edges 

Sharpen Edges is a Filter similar to the Sharpen Filter in that there are no Adjustment Sliders from which you can control its affect. It concentrates its sharpening technique to detecting edges and adjusting the contrast for those edges. As such, it works on the detailed areas of your image, leaving the flatter areas alone. This filter may be good for landscapes and other types of images with lots of details. As there are no adjustments, I usually do not recommend using this filter.

Guidelines For Using The Sharpen Edges Filter:
(1)    Create a new layer above your Pixel layer. Rename this layer “Sharpen Edges Filter”. This will allow you to Sharpen in a non-destructive manner.

(2)    Zoom in and expand your view (ie; 100%)

(3)    Select the Filter Menu

(4)    Select the Sharpen Menu 

(5)    Select Sharpen Edges (there are no Adjustment Sliders to use with this tool). 

d)    Filter --> Sharpen --> Sharpen More 

Similar to the Sharpen Filter, the Sharpen More Filter will apply a greater amount of Sharpening to a Pixel Layer (but once again, how much Sharpening is not known as finding any information about this Filter is extremely difficult). As there are much better Photoshop Tools available for Sharpening, I usually do not recommend using this as there are no Adjustment Sliders for you to control its effect. This Filter is still available, works and can be used when you need a fast and simple method to sharpen an image but care must be used as sometimes the amount of sharpening applied is too much for many images.  

e)    Filter --> Sharpen --> Smart Sharpen

The Smart Sharpen Filter is one of the more advanced Sharpening tools available in Photoshop. It contains the most amount of Adjustment Sliders and will produce excellent results when properly used. Some of its advantages include the ability to automatically detect and sharpen edges without creating noise (with a Noise Reduction Adjustment Slider), the ability to control the edge fade for Shadows and Highlights so image detail can be retained and when pushed to the extremes, will create smaller hallo’s. This Filter also contains a Preview option as well as a thumbnail image that can be zoomed separately from the main image. 

 
Guidelines For Using The Smart Sharpen Filter:
(1)    Merge all your Layers together into a single layer. Rename this layer “Smart Sharpen Filter”. Optionally convert this layer into a Smart Object so that you can later adjust these settings. 

(2)    Zoom in and expand your view (ie; 100%)

(3)    Select the Filter Menu

(4)    Select the Sharpen Menu 

(5)    Select Smart Sharpen

(6)    Set each of the Adjustment Sliders as needed for the image:

(a)    Preview – If you turn this on so as you made adjustments both the main image and the thumbnail image will display the results of your adjustments.

(b)    Preset – Initially set this to Default. Once you make adjustments you have the option to then Save these and load them for future images you may work on.

(c)    Amount – This Adjustment Slider represents the amount of Sharpening that will be applied and works in conjunction with the Radius Adjustment Slider. Typically, the more to the right you move the Amount Slider, the more Sharpening (contrast between lighter and darker pixels) will be applied. The more to the left you move the Amount Slider the less Sharpening will be applied. The Amount may be expressed as a percentage from 0% (no sharpening) to 500%. 

(d)    Radius – This Adjustment Slider is used to determine how much of each pixel being sharpened is affected. Typically expressed in Pixels, this setting controls the hallo created when an edge pixel is made darker or lighter. Radius has a big impact on sharpening because thicker edges make the increased contrast from the Amount setting more obvious.

Setting this adjustment to 1 means the contrast adjustment will be 1 pixel in size. Less than 1 will decrease the contrast adjustment to less than a pixel while increasing this to a value greater than 1 will increase the contrast adjustment to include more than a single pixel (from the edge). Depending on the image, this value is usually set to 1 or less so that the effect of the Sharpen enhances the detail edges but does not become too obvious. That being said, each image is different and should be treated as such. 

(e)    Reduce Noise – You can use this Adjustment Slider to somewhat reduce noise you may have in your image. Noise Reduction has a tendency of reducing an image’s sharpness so care must be used when performing this adjustment. Personally, I have found this Slider to be of little value and I prefer to perform my Noise Reduction as a separate task before beginning sharpening. Noise Reduction can be a complex subject and as such, it needs to be addressed during a future discussion.

(f)    Remove – You have several different options for how you want the Smart Sharpen Filter to work. These include Gaussian Blur, Lens Blur, and Motion Blur. 

Gaussian Blur typically causes the Smart Sharpen to behave similar to Unsharp Mask but with no edge detection ability (more about this later). Lens Blur allows the Smart Sharpen Filter to automatically detect edges and Motion Blur is typically used to  remove blur caused by moving subjects or camera shake (Motion Blur opens up the Directional option so you can help PhotoShop determine what Motion needs to be adjusted). 

Do not let these Names dictate which to use. Review how the pixels actually behave for the image in front of you and then make your adjustments accordingly.

(7)    If you select the > option, adjustments for Shadows and Highlights will appear. Under this option are 3 additional Adjustment Sliders:

(a)    Shadows

(i)    Fade Amount - The Fade Amount Slider acts as an Amount setting for applying sharpening in shadow areas of your image, but in a reverse manner (you would bee “Fading” or removing Sharpness). The higher the value (the more to the right you move this Slider), the less sharpening is applied. With the Fade Amount set to 0%, sharpening is not used in the image’s Highlights.

(ii)    Tonal Width – The Tonal Width Slider controls the range of shadows (darker pixels) that is affected by the Fade Amount. A lower Tonal Width limits the “fade” to affect the darkest edge pixels, where higher Tonal Width limits effect mid-tones. 

(iii)    Radius - The Radius Adjustment Slider controls the width around each pixel  to determine if the pixel fits within the specified tonal range. If it does, the pixel will be adjusted by the Fade Amount. Otherwise, it will not. Typically, a Radius of 1 pixel) is used but often times this setting should be increased.

(a)    Highlights

(i)    Fade Amount - The Fade Amount Slider for Highlights acts the same as for Shadows (it is used to “Fade” or remove Sharpness). The higher the value (the more to the right you move this Slider), the less sharpening is applied. With the Fade Amount set to 0%, sharpening is not used in the image’s Highlights.

(ii)    Tonal Width – The Tonal Width Slider controls the range of brightness (brighter pixels) that is affected by the Fade Amount. A lower Tonal Width limits the “fade” to affect the brightest edge pixels, where higher Tonal Width limits effect more of the mid-tones. 

(iii)    Radius - The Radius Adjustment Slider controls the width around each pixel  to determine if the pixel fits within the specified tonal range. If it does, the pixel will be adjusted by the Fade Amount. Otherwise, it will not. Typically, a Radius of 1 pixel) is used but often times this setting should be increased.

f)    Filter --> Sharpen --> Unsharp Mask

The UnSharp Mask is not actually a Mask as the name implies but a Filter. Although it is an early Photoshop developed tool, it is still in high use as it is quick and easy to learn and use. Although it does not have as many Adjustment Sliders as the Smart Sharpen Filter, it is still highly effective in helping to sharpen an image. Options for this filter include a Preview as well as a thumbnail image that can be zoomed separately from the main image, Amount, Radius and Threshold Adjustment Sliders.

Guidelines For Using The Smart Sharpen Filter:
(1)    Merge all your Layers together into a single layer. Rename this layer “UnSharp Mask Filter”. Optionally convert this layer into a Smart Object so that you can later adjust these settings. 

(2)    Zoom in and expand your view (ie; 100%)

(3)    Select the Filter Menu

(4)    Select the Sharpen Menu 

(5)    Select UnSharp Mask

(a)    Preview – If you turn this on so as you made adjustments both the main image and the thumbnail image will display the results of your adjustments. 

(b)    Amount – This Adjustment Slider represents the amount of Sharpening that will be applied and works in conjunction with the Radius Adjustment Slider. Typically, the more to the right you move the Amount Slider, the more Sharpening (contrast between lighter and darker pixels) will be applied. The more to the left you move the Amount Slider the less Sharpening will be applied. The Amount may be expressed as a percentage from 0% (no sharpening) to 500%. 

(c)    Radius – This Adjustment Slider is used to determine how much of each pixel being sharpened is affected. Expressed in Pixels, this setting controls the hallo created when an edge pixel is made darker or lighter. Radius has a big impact on sharpening because thicker edges make the increased contrast from the Amount setting more obvious.

Setting this adjustment to 1 means the contrast adjustment will be 1 pixel in size. Less than 1 will decrease the contrast adjustment to less than a pixel while increasing this to a value greater than 1 will increase the contrast adjustment to include more than a single pixel (from the edge). Depending on the image, this value is usually set to 1 or less so that the effect of the Sharpen enhances the detail edges but does not become too obvious. That being said, each image is different and should be treated as such. 

(d)    Threshold – This Adjustment Slider controls how sensitive Photoshop is when determining where edges exist. When the threshold is low there doesn’t need to be a big difference between two adjacent pixels for Photoshop to detect an edge. But as you increase the threshold, Photoshop needs to detect a larger difference between pixels to determine an edge exists.

g)    Filter --> Other --> High Pass

The High Pass Filter (HPF) is one of my favorite tools for sharpening as it is often quick, easy and accurate to use. Photoshop sharpening is all about locating edges and then increasing the contrast along these edges. HPF is basically an edge detection tool. It is used to find and highlight ledges and ignores non-edges. Once edges are detected, Layer Blending modes are then used to boost the contrast along these edges; all without affecting color or non-edge areas.

Guidelines For Using The High Pass Filter For Sharpening:
(1)    Merge all your Layers together into a single layer. Rename this layer “HPF Sharpening”. Optionally convert this layer into a Smart Object so that you can later adjust these settings. 

(2)    Zoom in and expand your view (ie; 100%)

(3)    Select the Filter Menu

(4)    Select the Other Menu 

(5)    Select High Pass (the Layer image will turn grey and white)

(6)    Adjust as follows:

(a)    Preview – If you turn this on so as you made adjustments both the main image and the thumbnail image will display the results of your adjustments. 

(b)    Radius – Set the Radius all the way to the left (to 0.1) and then slowly increase it by moving it to the right until the edges are beginning to be detected. When this happens you will see outlines begin to form as the light side of the edges become lighter and the dark side of the edges become darker. Those areas with no edges will stay grey. 

As the Radius effects the width of the detected edge, the more pixels you include, the larger the contrast between the detected edges. You will want to keep the highlighted edges to a minimum so usually 1 – 2 Pixels is enough (although some images may require more). For the best HPF sharpening results, try to find a Radius value that's large enough to highlight the edges while keeping the highlights small and as close to the edge as possible. Select the OK button when done.

(c)    You now need to change the Layer’s Blending Mode. The most common Modes used with the HPF are Overlay, Soft Light, Hard Light and Linear Light. In most cases, I use Overlay.

a.    Overlay produces a higher contrast effect, resulting in a stronger amount of sharpening

b.    Soft Light gives you lower contrast and more subtle sharpening

c.    Hard Light and Linear Light will give you higher contrast then Overlay

4.    Sharpening During Output Processing
An often overlooked aspect of digital image processing is to sharpen your image for the intended output. If displaying your images on the internet, whether it be on a web site or in social media, the viewing device resolution is usually low and thus you do not want your image to appear overly sharpened. Typically when displaying images on high resolution devices (such as on 4k and/or HDTVs) you will need a greater amount of detail, selective sharpening. Printing also usually requires extremely sharp images with very thin, non-detectable halos around the edges.

Sharpening Tips:

1.    Before doing any type of enhancements, first review your image and think carefully about what your image represents, the message you are trying to communicate and what changes (if any) may be needed to better communicate your intensions. 

2.    It is almost always best to do selective sharpening. This will usually produce a more compelling image. 

3.    Sharpening and Noise often have an inverse relationship (Sharpening can introduce Noise and reducing Noise can reduce an image’s Sharpness). Avoid trying to sharpen images that have a lot of Noise. It is also best to first try to reduce or eliminate the Noise prior to sharpening as sharpening may intensify the Noise; thus making it harder to then get rid of it.  

4.    When doing any type of sharpening to an image, it is usually best to do so when viewing your image at or near 100% so that each image pixel uses one screen pixel; giving you the most accurate sharpening view.

5.    One method to find the best sharpening settings is to use a low Radius (ie; around 1 or 1.5) and then set the Amount Adjustment Slider all the way to the right. This takes the sharpening effect to the extreme and will produce large halos. Then start to move the Amount Adjustment Slider to the left until the halos disappear. 

6.    Always make sharpening adjustments in small increments so that you can clearly see the affect your sharpening is having on your image.

7.    If you Sharpen your image on a separate layer, you can change that Layer’s Blending Mode, Opacity and or use Masks. This will help you avoid color shifts along the pixel edges as well as eliminate those areas you do not want sharpened.

8.    When working with high resolution images, increasing the amount of sharpening contrast is usually less noticeable then when working with lower resolution images. This is because higher resolution images have a greater number of pixels to work with.

9.    Photoshop can only sharpen one layer at a time so if you have multiple layers, you may need to combine them into a single pixel layer before sharpening. 

10.    Convert your Sharpen Layer into a Smart Object. This will allow you to later go back and re-adjust your Sharpening Adjustment Settings. In this manner, you can use the same image for different types of output.

Sharpening Myths & Limitations

1.    Some people believe that Sharpening can help bring an out of focus image into focus (or at least improve it). Unfortunately, this is not the case. Sharpening can only use the pixel information that is available and cannot by itself, create sharpness where it does not already exist. If the subject or object in an image is blurry, Sharpening will only make it seem more so. 

Photoshop does includes a Shake Reduction Filter (Filter  Sharpen  Shake Reduction) which is designed to automatically detect motion blur in an image (ie; caused by movement when taking a picture) and counteracts it with sharpening and ghost removal logic. Although not always useful, it can at times be used to reduce or eliminate some amount of motion blur.

2.    At times, there is also a tendency to “Over Sharpen”. An image becomes Over Sharpened when the edges between the pixels become so pronounced the viewer can see the actual differences between the dark and light pixels. When this occurs, a Halo will start to appear along the edges. The greater the Amount of Sharpening and/or the greater the number of Pixels used to determine the edge, the larger will be the Halo. If when sharpening an image, you start to see these halos forming, try reducing the Amount or Pixels to eliminate them.

3.    In many pictures over-sharpening is an undesired effect as it makes our subject seem unnatural. In other cases, however, this can be intentional as a unique style of the photographer whose work may be perceived as more artistic. 

As we have seen, there are many decisions to make when Sharpening a digital image. From when to sharpen, what tool to use, and how much all become important factors in trying to get the most out of your image. As such, Sharpening may take time and practice to master but ultimately it becomes an extremely useful tool and an expression of your creative image making process. 

For more information about the concepts, techniques and tools of digital photography, see my blog at https://www.mfaimages.com/blog

References
https://helpx.adobe.com/photoshop/using/adjusting-image-sharpness-blur.html

https://lenscraft.co.uk/photo-editing-tutorials/photoshop-image-sharpening-options/

https://improvephotography.com/45000/4-photoshop-sharpening-techniques-landscapes/

https://www.photoshopessentials.com/photo-editing/sharpen-high-pass/