Some Digital Photography Techniques

I've always loved photography, and even had a small darkroom when I was a kid.  But I never got very good at the processing end of things, and never progressed past black and white.  With digital photography that has all changed - techniques that were difficult or nearly impossible in a dark room can become nearly trivial in Photoshop or a similar photo editing package.  I feel like I've been waiting all my life for digital photography to arrive!  If you are still not convinced to make the switch from film, or would like more information about the difference in capabilities between digital and film here is a useful and technical comparison of  Film vs Digital.

You do not need to spend the money on Photoshop for a good graphics editing program; there are a number of capable photo editing applications available.  The Gimp (GNU Image Manipulation Program) is very capable open source, and free, software that can be readily downloaded.  It has pre-compiled versions for many platforms.  Here's the link to the Gimp pre-compiled Program for Windows. And of course there are many applications available for sale, including Paint Shop Pro which has many capabilities similar to Photoshop and retails for well under $100. Another good option, for the same price is Light Zone. LightZone is a bit different from some of the others mentioned above in that it specializes in adjusting lighting effects in digital images.

Here are some direct links to the topics below:
Digital Camera Noise Reduction
Restoring Faded Colors for Scans of Old Photos
Increasing Dynamic Range with Multiple Exposures
Depth of Field Trade off - Aperture vs Diffraction
Increasing Depth of Field with Multiple Exposures
Scope Adapter
Legal Information for Photographers
Links to Various Tutorials


Digital Camera Noise Reduction

Digital cameras generally do very well in a brightly lit scene, but some 'noise' can creep in for dark areas or those in which the ISO (equivalent digital 'film speed') has been increased for low light level conditions.  The short explanation is that in any electrical sensor there is some very small random signal ('noise') present.  For a digital camera image sensor, dark areas of a photo correspond to very little signal (light) reaching the sensor.  Thus the desired signal is not much larger than the random 'noise', which can lead to a speckled appearance.  Turning up the ISO setting for a low light level magnifies this noise.  Some higher end cameras have various techniques for dealing with this, but you can still end up with the grainy appearance in your photos.

Avoiding or minimizing noise can begin with the exposure settings on your camera, as discussed in this Expose Right Tutorial  (exposing for maximum Signal/Noise - S/N - ratio by moving the bulk of the histogram towards the 'right' or higher signal end.

Photoshop and Paint Shop Pro both have built-in software capabilities for reducing digital noise, and there are a number of other products on the market developed specifically for this purpose.  Here is a Review Of Noise Reduction Software.   I have found Picture Code's Noise Ninja to work very well.  Below is an example.  The left pane is the original image, which was badly underexposed.  The second pane shows the result of adjusting the RGB levels to obtain a better exposure.  The exposure and colors are much improved, but at the cost of a very grainy/speckled appearance.  The third pane shows what Noise Ninja was able to do for reducing the noise.

Digital Noise Reduction Example


Restoration of Color For Scanned Photos

One very big advantage of digital imaging is being able to archive and restore old film photos.  Once in digital form it will never fade, and very often much of what was lost can be restored.  Before simply buying the first scanner you find, however, you should learn a bit about scanning so you do not later have to repeat what you've done.  A few scan tips is an excellent resource for getting started.  This resource has been around for awhile, but the basics in terms of resolution, dynamic range, histograms, etc. have not changed.  Thoughts Upon Scanning  is also a very worthwhile read before getting started.

Some basic photo editing skills can easily do a great deal to correct many faded and color shifted photographs without any additional software.  The earlier these skills are applied in the scanning process, the better the overall result.  However, satisfactory results can often be obtained by adjusting only in the "post processing" phase of things, if that is all you have to work with.  Here is one Restoration of Color  (ROC) Plug-in for Photoshop  which greatly automates the adjustments.  

For an advanced reference, the Digital Retouching Book  has loads of good information.  Finally, a good scanner and software can do much right during the scanning phase.  The scans below were made using the Nikon 5000 Slide Scanner with the automated Restoration of Color option turned off (left) and on (right).  The image on the left is pretty much what you see when you hold the slide up to the light.  This same effect can be approximated with the scan on the left in post processing, but not as well.  That is because the scanner is able to use the full 16-bit depth from the scan sensor to create the 8-bit final result.  When post processing, you are starting out with an 8-bit image and 'stretching' the more limited amount of information, which can result in 'banding' and a blotchier result.

Restoration of Color


Enhancing Dynamic Range By Multiple Exposures

Capturing a photo with a wide range of lighting can be very difficult, as the image sensor can only capture a range of lighting levels much lower than the eye is capable of seeing.  For a dynamic, moving scene there is little you can do about this, but for a stationary scene you can use a tripod and make multiple shots at various exposures.  Many cameras will allow you to automate this by using an "auto bracketing" setting, which will quickly and automatically take multiple shots at a range of exposure settings.  If done correctly, even the lightest and darkest regions will be properly exposed in at least one of the images.  All that remains is to then combine the correctly exposed portions from each.  There are at least two ways to do this, one of which is a manual method using layers and masks, and the other is highly automated using special software.

Layers and Masks

This method does not require any software other than your normal image editing application, and gives you complete control over the result.  One very good description of this technique is described by Larry Bolch's Bracketing and Layers Tutorial.  As the details are well covered in the tutorial (along with some stunning examples), I won't say any more about those.  Below are two examples of this method, both of which show the original images as thumbnails, along with the final result.

Layer and Mask Example 1


Layer and Mask Example 2

Photomatix Automated Software Method

There are a number of automated packages which accomplish essentially the same thing.  One which I have found to be highly effective is Photomatix, which not only automates the combination of exposures as seen above, but also adds a Tone Mapping option.  This is additional processing by the software to enhance local contrast details.  The result can sometimes be surreal, but is often very dramatic.  See the web site for some excellent examples.  The image below shows a comparison of methods for a single image.  In this case there is only one exposure, which is shown on the left.  The exposure is good for the clouds, but all else is underexposed.  It was easy to adjust the levels to obtain proper exposure for the tree and windsock, but at the cost of losing all sky detail.  The second two images are combinations of the original and adjusted image.  In the layers and masking method, the two images were placed in separate layers of a single image.  The tree and windsock were 'selected' using Photoshop's selection tools, and then masking was used to pick which layer was used for the selected region.  This was a slow process, and some small areas where the selection were not perfect (bright white areas in the tree foliage) are apparent.  The third pane shows the automated result from Photmatix, with the Tone Mapping option turned on.   

Processing Comparison



Depth of Field Trade off - Aperture vs Diffraction

In Macro Photography it is tempting to set the maximum aperture number (minimum diameter opening) to obtain the maximum Depth of Field, and then blast it with enough flash to get the correct exposure. However, you may end up gaining depth of field but losing sharpness if you go too far. That is because of Diffraction. As the aperture opening becomes very small, diffraction begins to degrade the image. At what point this happens depends on the sensor (actually, the individual pixel) size and other factors. However it is easy enough to determine with your own camera and lens.
Diffraction & DOF test
The above pic shows a folded text page that was used. The left side was parallel to the lens, and the right side was folded away from the lens. The lens was focused on the left side. A series of pics were taken at different aperture settings, and then combined and labeled as shown below. Click on the image to see the full size result.

Check the full size result carefully. You will see that more of the text on the folded right portion comes into focus as the aperture (f-stop number) is increased. But also pay close attention to the 'R' on the left side. The camera is correctly focused for this region of the page, and it is sharp and clear for all the low f-stop numbers, but begins to lose sharpness somewhere around f20, and is quite degraded by f45.
Now, none of this means you shouldn't go to the very high aperture numbers if you absolutely need to get the depth of field, but realize that the depth of field comes at a cost. If you can get the photo with a lower aperture, then that is the best choice. Do your own tests, and decide what works best for you.

Increasing Depth of Field (DOF) Via Multiple Exposures

Macro photography is relatively simple for completely flat surfaces.  However, for 3D objects it can become very difficult to get more than just a very small region into focus.  I won't go into the why of that here, as this Depth of Field Tutorial and Depth of Field Articles and Information provide a wealth of information on the topic.  I tried several methods of combining multiple exposures (similar to the  Enhancing Dynamic Range method describe above), but with much less success.  This included several different software packages.  I finally found one package that works well and is reasonably priced.  The images below were combined using Helicon Focus in a mostly automated process.  The software can even adjust for small shifts in the image between frames.  Note: the image below is of a small bit of dried plant matter of no particular interest in itself.  It just happened to be handy to the microscope when I was looking for something to experiment with.

Stacking Multiple Exposures to Increase DOF

Scope Adapter

There are a number of adapters on the market which will adapt nearly any camera to a microscope or telescope.  I bought the complete MaxView Plus kit from Scopetronix. This kit has adapters for a variety of telescope and microscopes, and interfaces to the camera by an additional, special adapter.  To switch to another camera only the adapter for that camera needs to be bought.  There are also many other adapters available.  Here are 3 samples using the MVP kit with a Nikon 5700 camera.  The left image is a prepared slide viewed through a Nikon microscope.  The middle photo is of a bee's eye, made using only the MVP adapter.  The right photo of Saturn was made through a Meade 8" Schmidt-Cassegrain telescope.

Scope Pics


Photography - Some Legal Information

In the world since 9/11 many people have become sensitive to people taking photos in public places.  This can even lead to confrontations with Law Enforcement personnel who may not be completely familiar with the laws themselves.  I make no claim to offer any legal advice here, however here are some links that may provide useful information:

The Photographer's Right has a down loadable Adobe PDF file which is printable guide to common photography law, written by a lawyer.  It is a handy guide to print and carry in your camera bag for those times when you may be accosted by well meaning, but mis-informed individuals.

State by State Privacy Guide is a compilation of laws by state with respect to photography and invasion of privacy legal rulings.


Some Processing Tutorials

Larry Bolch's Web Site  contains a number of excellent tutorials, some of which appear in links above.

Laurie McCanna's Digital Techniques has a number of useful tutorials for Photoshop and other image processing programs.

Digital Imaging Help has a large number of useful links to most all aspects of digital imaging.

Photoshop and Paint Shop Pro Tutorials

Digital Photography Workflow is a suggested series of processing steps by one photographer.


(updated August 15, 2012)
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