Thursday, April 3, 2014

On Sharpening Images

How To Achieve A Base Level Of Sharpness

This article is designed to provide a specific practical flow of work for providing an overall, high quality base level of sharpening using ACDSee Pro 7. Because I have a compulsive need to provide detail and explanation, I have included some background information on sharpening in general. As a result, users of software other than ACDSee Pro 7 might find this text useful.

My advice regarding the various scalar levels of the controls, and how the controls are operated by the user, are specific to ACDSee Pro 7. Other software may (and probably will) require different levels and a will offer a different User Interface for the controls they provide.

A word of warning regarding the relationship between sharpening and noise. It has been my experience that people start to worry about noise too soon. One of the great ironies of digital photography is that noise can actually increase the appearance of sharpness. It is my belief that sharpness often gets ignored or compromised in the rush to eradicate any hint of noise. Finding the ideal compromise between noise and sharpness can be difficult, but I think the techniques I describe can at least lessen the pain and make having sharp images a pretty consistent experience for you.

My advice is to sharpen first without regard to noise. Then when the Base level sharpening is complete (and perhaps after detailed sharpening as well), only then attempt to find the balance between noise and sharpness. I find myself much happier with a sharp and slightly noisy photo than I am with a “creamy” and “plastic” photo with little detail.

If you do any research, you will discover that my advice is the opposite of what many pundits believe. I think their advice is built around the idea that noise is the greater problem over sharpness. I have not found that to be so from my own practice. However you decide to order your noise reduction and sharpening tasks, I think my advice will still help you achieve the maximum sharpening of your photos possible considering the other processing choices you have made.

What is Sharpness?

When discussing sharpness in photography, two words need to be understood, “resolution” and “acuity”.

Resolution is pretty much an “In Camera” feature. This is the ability of the sensor in your camera to distinguish closely spaced objects and parts of objects in your photo. You will often see in camera reviews, photos of closely spaced lines that placed in increasingly close proximity. The ability to see these lines as distinct and separate lines is a good measure of Resolution.

Acuity is the measure of how the edge between different adjacent objects transition from one object to the other. In the example of the lines above, the black bars could be considered one object, while the white spaces between them could be considered another object. If the edge of those black bars is sharp and distinct, the acuity is high. But if the transition between the bars and the white space fades from black, to shades of gray, and only then to white, then the acuity is considered low. Acuity is considered to be an aspect of the combination of your lens and the type of photo processing you do.

Clearly, resolution can be improved by the acquisition of a new camera with a better sensor. Though making sure that your camera doesn't move or shake during the exposure can help you capture all the resolution your sensor can provide. Learn to hold your camera steady when taking photos.

However, to improve acuity, if you have a camera with interchangeable lenses, you can buy a better lens. And regardless of the quality of your lens, acuity can be improved by careful selection of photo processing techniques.

There are 3 Types of Sharpening

It is important to remember that there is no single sharpening step in post processing a photograph. There are three types of sharpening, each performed at different times of the development and editing process. 

Base Level Sharpening - This provides the level of overall sharpness found in a photograph. It can include any sharpening done within the camera itself, but it also includes any sharpening you might do in the “Develop” Tab of ACDSee Pro 7 or the equivalent section of other tools. Often this is the only thing that many people think of as sharpening. This type of sharpening is the subject of this tutorial.

Detail Sharpening - This allows the photographer to selectively sharpen (or soften) specific areas of a photo for the maximum effect on the viewer. This used to be the exclusive domain of an external editor, but the addition of the Develop Brushes in the “Develop” tab of ACDSee Pro 7 allows the photographer to move much of this sharpening to the developing step.

Output sharpening - This type of sharpening is often forgotten by beginners, and sometimes even by experienced photographers. The reason it is needed is that, sometimes, preparing a photo for publication to the internet, a magazine, re-sizing it, or just printing, will soften an image just a bit, and the photographer will wonder why his or her photo just doesn't look like it did in ACDSee Pro 7.

Additional notes on Base Level Sharpening - Unless, I am shooting jpgs straight from the camera for immediate use, I prefer to do my base level sharpening during the post processing phase. Actually, even pre-sharpened jpgs, while pretty good straight from the camera, can often be improved by additional sharpening or selective softening.

Many Workflow tools like ACDSee Pro 7, as well as Lightroom and others, now have the ability to do detailed sharpening at the same time as the Base level sharpening. 

It has been my experience that is a tricky line to negotiate. I have personally found it useful to separate Base level sharpening from the Detailed sharpening. I find myself starting to concentrate on details, long before I have created the best possible level of base sharpening. I wind up with a mediocre base level of sharpening, which I then go in and fix with detailed sharpening. But if I had done a better job on the Base, I wouldn’t have had as much to fix in Detail. 

Additional Notes on Output Sharpening - This sharpness adjustment is often subjective and according to taste, but it is absolutely essential if you want your viewers to get the full effect of a given photo. This is usually done AFTER the developed photo has been completed and any creative edits are made, and after the developed photo (which is usually raw, at least for me, but it could be a tif or jpg file format) is converted to the bit mapped distribution format, which for me, is usually an appropriately sized jpg file.

Because of this, the ACDSee Pro 7 “Edit” tab is most useful for this functionality, as would also recommend that this sharpening be done outside any non-destructive editing tool. One doesn't really want these distribution specific edits permanently incorporated into the developed version since future sharpening and distribution needs may not be predictable.

The Differences Between the Develop and Edit Tabs

While my comments above, specifically address the ACDSee Pro 7 infrastructure, the "Develop" and "Edit" model is relatively common in photographic software in general.

Lightroom and a few other software titles appear to want to blur the line between the develop and edit modes, placing almost every change it can make to a photo in the "Develop" tab and leaving the "true" edit mode to external editors. There is no right or wrong in this, just subjective preferences. 

The “Develop” mode

In general, “Develop” refers to the non-destructive sort of editing found in most raw developers. An XML text file is created for each photo and all changes to the photo are stored in that XML file. This is sometimes referred to as a “Side-car” file.

Changes made to the photo are applied to the photo you see on screen, but NOT to the photo stored on the hard drive. Instead, the changes are stored in the XML file. Then, the each time you display that photo in ACDSee Pro 7 or your favorite non destructive editor, that XML file is read and the cumulative changes you have made to the photo are applied to the photo you see on the screen, print, or the exported photo you convert a photo to a different file format. 

The Practical effects of this information

This non destructive “editing” comes at a cost though. First, there is a lot of extra work for the computer in terms of keeping track of the XML file, keeping it associated with the right photograph, and displaying the changes properly to that photo when it needs to do sp. But It’s a computer, it doesn’t care how much work like that it has to do.

The other cost affects us more directly. If you want someone to see a photo who doesn't have ACDSee Pro 7, or your favorite raw developer, that XML file is useless to them (even if they have another program that uses XML files). The reason is, while XML files are ‘universal’ and available to any who want to use them, HOW those XML files are used by your favorite software are unique to each Software program you use. 

One advantage of the non destructive sort of development is that the photographer can easily remove the changes made to the photo by deleting the xml file or editing it so that the changes no longer desired are eliminated.

So creating a tif or jpg file with the changes and edits applied is the only practical way to distribute and share a photo.

The “Edit” mode

Editing refers to the traditional manipulation of a photo as found in conventional Bit mapped editors. Any editing changes are made directly to the photo displayed on the screen, and while changes may, or may not, be stored in temporary memory, they are not saved to any file other than the photo itself. As a result, the only permanent record of changes that have been made are the cumulative changes made to the displayed photo and those changes are only saved when the photo itself is saved to the Hard drive.

In ACDSee Pro 7, the sharpening controls of “Amount”, “Radius”, “Mask”, “Detail”, and “Threshold” are the same in both modes, and function in the same way. However, the big difference is that you can undo the sharpening in the “Develop” tab at any point, but once the image is saved in the “Edit” tab, the changes are permanent and can not be undone.

Clearly, it would be wise to do as much sharpening as possible in the “Develop” tab rather than in the “Edit” tab. But I would recommend that Output sharpening be done in the “Edit” tab. 

Why? For the non destructive editing that the “Develop” tab does, all changes to the photo are stored in an XML file. Each time you display a photo with an XML file, ACDSee Pro 7 reads this file and then applies these changes immediately to the image on the screen and the display copy in RAM (Not to the image saved to disk.)

How to Sharpen a Photo with ACDSee Pro 7

Before we can discuss sharpening a photo with ACDSee Pro 7, we need to have a basic understanding of the controls ACDSee uses to create and modify sharpness.

Users of other software will find this section pretty useful, I think. In my research for this article, it became obvious that sharpening controls don't differ all that much from one piece of software to another. While the ACDSee specific advice might have marginal value to non-ACDSee users, the basic definitions and strategies will have a practical application to them.

ACDSee Pro 7 Sharpening Controls

As stated earlier in this article, the sharpening controls between the "Develop" and "Edit" tabs are essentially the same. So I have arbitrarily decided to use the sharpening controls in the "Develop" tab as a point of reference. Above, is a screen print of the ACDSee Pro 7 sharpening controls in the "Develop" tab, with them resting at their default values.

The Amount Control

The ”Amount” slider controls works in conjunction with the other control settings. However even with the other controls at the default settings, there is still some change as the slider is moved, since the default settings are just that, settings.

The amount of sharpening change occurs by adjusting the amount of contrast around the edges of objects in a given photo. When the slider is “zeroed out” (all the way to the left) no sharpening change occurs and the more you move the slider to the right, the more sharpening changes occur.

How to get comfortable with this control:

  1. Select a photo with faces, leaves (grass or tree leaves are good), and possibly with some big text such as signs.
  2. “Zero out” all the sharpening controls. In ACDSee Pro 7, you can do this by placing the cursor on a slider control, and right clicking the mouse button. This will place that control in either the “Zero”, or absolute minimum effect position. On some controls that will be all the way to the left, on at least one control, it will be in the middle.
  3. Without setting the Radius or Detail controls, move the slider to the right, notice the level of sharpening that occurs. This is the level of sharpening that can occur with the other controls “zeroed out”.
  4. Now set the Radius and Detail controls to taste, and then move the Amount control. Note that the quality of the sharpening change that occurs is different. This control is very much dependent on the parameters set, or not set, in the other controls.
The Radius Control

To successfully use the Radius control, you must first decide if the detail in the photo is fine, coarse, or somewhere in between. This decision will affect how you want to set the Radius control.

The Radius control specifies the number of pixels to adjust around the edges of each object. Higher values will work best for coarser detail while the lower values work best for the fine detail. By setting this control first, you won't actually see any change to the photo as you set this control since you aren't making any changes, merely setting one of the parameters for when you ultimately will move the “amount” slider control.

The Radius control for sharpening is a slider bar with a scale increment varying from 1 to 20. Unfortunately, the ACDSee Pro 7 documentation doesn't appear to state with certainty that the increment numbers enumerate the number of pixels from the edge that are affected, though my experiments with this control tell me it is reasonably close to the absolute number of pixels affected. I believe from a day to day, operational point of view, it is safe to interpret the values as the number of pixels deep into the edge that the change will affect.

How to get comfortable with this control:
  1. Select a photo with faces, leaves (grass or tree leaves are good), and possibly with some big text such as signs.
  2. “Zero out” all the sharpening controls. In ACDSee Pro 7, you can do this by placing the cursor on a slider control, and right clicking the mouse button. This will place that control in either the “Zero”, or absolute minimum effect position. On some controls that will be all the way to the left, on at least one control, it will be in the middle.
  3. Set the Radius slider control all the way to 20. and then move the Amount Control slider to the right. You will notice that the faces and the leaves start to develop a many pixels deep border (called a “halo” by ACDSee) as you move the amount slider to the left, yet coarse detail like the big letters in the signage seem unaffected. This is because the faces and the leaves are often considered fine detail and fine detail is more susceptible to the “halo” effect.
  4. Now, move the Radius slider to between a “2” and “5”, and then repeat moving the amount slider, You will likely notice that the “halo” border that develops on the faces and leaves is almost non existent. It may even refuse to develop at all; yet there is a subtle, but real, overall sharpening effect that you can see, while the sharpening on the signs is VERY minor. If that border halo develops around the fine detail, move the radius slider control closer to “1” till it disappears. There will still be some level of sharpening as you subsequently move the Amount slider control.
Clearly the Radius control is subtle, but very important, in terms of creating the illusion of sharpness. But it is important to remember, that the edges this control “sees” aren't always the edges you think of as important. This control affects the whole of the photo, what I call the “logical” edges including noise and texture, and not those edges a reasonable person might see as important, those I call the “rational” edges.

The Masking Control

The Masking control targets the edges of objects while ignoring the sharpening of noise and texture, which can occur with the other controls. This control attempts to emulate the sharpening masks that can be created in typical mid level editors and above. Is it as effective as a bit mapped sharpening mask? I think so. Certainly, it is much more convenient, and it does have certain advantages over an editor based sharpening mask.

First of all, it can be done in both the ”Develop” and ”Edit” tabs of ACDSee Pro 7. Since the ”Develop” tab of ACDSee Pro 7 is non destructive ”editing”, that means, if you don't like what you have told it to do, it is easy to reverse what you have done. And in either the ”Develop” or ”Edit” tab, it doesn't require the use of layers. If you are new enough to bit mapped editing that you are uncomfortable with layers, this offers a pretty good alternative.

I also like the easy control this tool provides over edge sharpness. At lower settings, this tool looks for edges within the body of objects, but as you move the slider more to the right, the relatively minor interior edges are ignored and greater emphasis is placed on the more delineated object edges.

You need to be careful to find the right balance for this. I've discovered that a slight halo begins to appear around object edges as the slider is moved to the right. In this situation, the object edges do become sharper, but that halo slightly offsets the greater sharpness the tool provides. At normal viewing magnifications, or normal viewing distances for printed material, this halo isn't too noticeable, but if you magnify the image beyond what is considered normal, or if you expect viewers to get “up close” to a print, you will want to make sure that halo is at its minimum.

I've found that for foliage, and small detail objects, along with people (especially bare heads and skin) a low to medium masking value is useful. For those more coarse details, a higher masking value will work well.

In ACDSee Pro 7, if you just slide the slider to the right you won't see any change or accommodation to the photo at all. To see the edge delineation level, you need to press the “Alt” key as you move the slider to the right. Doing this, you will quickly see how the tool identifies the various edges found within the photo.

How to get comfortable with this control:

  1. Select a photo with faces, leaves (grass or tree leaves are good), and possibly some big text such as signs.
  2. Set your Radius, amount, detail, and threshold according to taste.
  3. “Zero Out” the Masking slider. In ACDSee Pro 7, this will be at level “0”.
  4. Move the slider gradually to the right, while pressing the “Alt” key. Note that at “0”, the image is completely whitened out. As the slider moves to the right, the interior edges of objects start to appear in black. As the slider moves further to the right, the object edges gradually start to appear in white, and the interior edges grow together in black. This is a visual representation of the sharpness masking layer found in bit mapped editors.
The Detail Control

I'm not all that comfortable with the Detail control description in the ACDSee Pro 7 help file. It may be accurate from a technical perspective, but it doesn't really give us any help in figuring out how to use it and I don't think it is complete in its description. (Look it up if you're curious. Getting comfortable with the help file is a GOOD thing!).

Instead, I like to think of it as providing us the ability to fine tune the effect of the combination of the Radius and Amount controls. It allows us to shift emphasis from fine to coarse within the spectrum already delimited by Radius and Amount, and it can reduce the size of the halo generated by the combination of the settings in the Radius and Amount controls. Moving the Detail slider to the right shifts sharpening emphasis to fine detail while shifting to the left emphasizes the coarser elements.

How to get comfortable with this control:
  1. Select a photo with faces, leaves (grass or tree leaves are good), and possibly with some big text such as signs.
  2. Set your Radius and Amount according to taste.
  3. “Zero Out” the Detail slider. In ACDSee Pro 7, this will be at level “50”, with an equal amount to the right in the slider as there is to the left.
  4. Zoom into a key area (from a sharpening perspective) of the photo. Depending on the photo, the zoom ratio could be as much as 200% - 300%. The goal is to see clearly the edges of the objects and those transition areas that define the edges.
  5. Move the slider to the left. Note that the image gets a tiny bit softer as does any halo that might still be there. Then move the slider to the right, note that sharpness goes up and the halo gets a bit more defined.
If you are happy with the level of sharpness and the halo generated by just using Radius and amount, there is no need to use the “Detail” Slider. Just leave it at the default setting of “50” for ACDSee Pro 7 (other software may use a different value scale, but you get the idea, I hope.)

Also, remember that the amount of change this control can make varies with the level of overall sharpening defined by the combination of the Radius control and the Amount control. This control is highly dependent on the other sharpening controls.

It is also good to remember that like the “Radius” control, the edges this control “sees” aren't always the edges you think of as important. This control affects the whole of the photo including noise and texture, what I call the “logical” edges, and not those edges a reasonable person might see as important, those I call the “rational” edges.

Threshold Control

Threshold controls the level of difference in pixel brightness within an object's edge must be before sharpening can occur.

So, sharpening can occur only if two adjacent (or physically close) pixels are different enough to overcome the threshold level you set. The higher values tend to sharpen strongly delineated edges and tend to ignore background noise. Lower values tend to sharpen both the edges of objects and the logical edges in their interior. As a result, at lower levels, noise also tends to get sharpened. I think the Threshold control could be reasonably described as a very mild Masking control.

ACDSee recommends that you set the threshold high enough to enhance the edges while minimizing the background noise. My experience indicates this is essentially correct. I think one gets better and more distinctive control over edge sharpening with the Masking control, however. But this tool is quite effective in adding just a mild boost to sharpness without excessively affecting noise.

The further to the LEFT the control slider resides, the more change that moving the Amount control to the RIGHT will display in terms of sharpness though at the cost of increased noise.

This control isn't really designed, however, to register large changes in sharpening. It seems its real function is to help you find a balance between noise and sharpness without excessive softening. If I need more edge sharpening, I use the Masking control.

How to get comfortable with this control:

  1. Select a photo with faces, leaves (grass or tree leaves are good), and possibly some big text such as signs.
  2. Set your Radius and amount according to taste.
  3. “Zero Out” the Threshold slider. In ACDSee Pro 7, this will be at level “0”.
  4. Zoom into a key area (from a sharpening perspective) of the photo. Depending on the photo, the zoom ratio could be as much as 200% - 300%. The goal is to see clearly the edges of the objects and those transition areas that define the edges.
  5. Move the slider gradually to the right, note that edge sharpness goes up very slightly and a very slight “creaminess” starts to appear in the interior of the objects.

Suggested Base Level Sharpening Workflow

  1. Set your base level exposure, white balance, and color controls. Don't concern yourself with cropping, or black and white conversion if that is your goal. At this point we are interested in developing a good, well exposed and color corrected photo with which to work.
  2. Decide if you are going to use the Develop tab or the Edit tab in ACDSee Pro 7. If you don't know, or don't have a strong reason to do otherwise, I recommend that you use the Develop tab for this step.
  3. Decide if the photo requires a fine detail strategy or a coarse detail strategy. In my experience, a coarse detail strategy is relatively rare.
  4. Set your Radius control. If you feel the need to go higher than, say, 4 on the radius scale, know that you are starting to pursue a medium coarse sharpening strategy and you might find detail in grass and leaves or hair to be less than you might want. I would suggest a “2” as a starting point for Radius.
  5. Set the Amount control according to taste.
  6. Set the Detail control. Remember, this sort of fine tunes the combination of Radius and Amount. If you already like the sharpness neighborhood that Radius and Amount put you in, you don't need to use this control. But it's there if you need it.
  7. Set the Threshold to whatever standard you are comfortable with. I use an “8” in ACDSee as a default, and if it seems inadequate, I adjust to taste.
Now examine your photo. Is it sharp enough overall? Remember, this is for the overall sharpness, ignore those areas that need specific sharpness changes if you suspect getting them “right” will ruin the overall sharpness of the photo. Remember that you can always address those specific areas in your Detailed sharpening step.

Ask yourself, "Will adjusting one of the above mentioned controls make things better, or, are you reasonably certain that they are set properly?" If you are reasonably certain that the prior controls are reasonably well set, then you might want to move on to the Masking control or you may decide to fix the issues you see in the Detailed sharpening phase.

After that, we are free to address other issues such as additional noise control, B&W conversion, special effects, etc.

There you have it. This is pretty much how I sharpen my photos. I'm pretty happy with the sharpening I now get from my images and I am now going back and redoing a large number of “old” photos that I no longer consider sharp enough.

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