Imaging the Natural World

Classes Starting

It’s that time of year again and my series of 10 two hour classes covering digital photography will begin on Wednesday.  See the side bar of upcoming events for details of each of the classes being offered at the Granite Street Gallery in New London.

The new format of two hour classes each built around a distinct portion of digital imaging is proving popular. It allows those interested to choose just the classes that they feel will benefit them. Making half the classes available on Wednesday evening and the other half on Saturday mornings and then interchanging the topics for the next season’s schedule also allows students to fit classes to their personal routines.

Notes from the classes are made available to students on Acrobat.com after each class.

Details Enhancer & Photomatics Pro

In the last post, I featured the HDR processing of five images using the Tone Compressor option of Photomatics PRO. Below is the same set of images processed using the Details Enhancer option. 

The Photomatics user’s manual indicates that the treatment of pixels using the Details Enhancer is affected by surrounding pixels and therefore not a global effect. This results in great control of the amount of detail revealed by local contrast. The number of controls available using the details enhancer option is much more extensive  than with the tone compressor option and it can result in images that are far from “natural”  looking.  In the case of this image, it enabled revealing of the detail in the rock formations which was discernible by eye, but not revealed well using the tone compressor option.

Which do you prefer?

More on HDR & Photomatix Pro

I continue to be fascinated with HDR imaging and I am slowly beginning to understand the use of Photomatix Pro in creating an image that represents what I saw as I created the images that underly the HDR merged result.  Photmatix Pro provides three separate approaches to creating an HDR image:

1. Exposure blending
2. Details Enhancer
3. Tone Compressor

I decided to experiment with each approach using the same images for a starting point. According to the Photomatix manual, the Tone compressor works on a global basis or “pixels are processed independently of their surroundings.” The method produces a more natural looking result than the Details Enhancer approach.

Below is an image processed using the Tone Compressor tools.

HDR Image Processed Using Tone Compressor Controls

More from the Southwest

I don’t often shoot panoramas, not because I don’t like them, but because I don’t think of it when the opportuntiy presents itself. The Digital Imaging Association conference that I participated in  this month in Page Arizona included attendees who are panoramic  photographers. Their discussions heightened my awareness of opportunites.

Monument Valley Panorama

The above image was stitched from two separate images using Photoshop CS4. One of the things I learned from the group is that stitching programs are so good today that even hand held images can be successfully merged into a single panorama. I still advocate the use of a tripod, not for stitching success but for the highest quality image results. This particular panorama was shot hand-held with an image stabilized lens.

High Dynamic Range (HDR)

High dynamic range imaging allows the building of a single image from multiple images that when taken together can far excede the dynamic range of tradional film emulsions. The image below is the result of combining  five images spanning about 12 f stops.

HDR Image Bryce Canyon- Arizona

The images below are the five individual images from which the composite was blended using PhotoMatrixPro’s exposure blending option. The ability to render detail in the deepest shadow areas while retaining detail in the highlights is obvious.

1/3000 @f/9

1/750 @f/9

1/180th @f/9

1/45th @f/9

1/10th @ f/9

From now on whenever my histogram tell me I cannot capture the full tonal range of a scene, I will turn toi the new tool in my arsenal.

Antelope Canyon

On Monday morning our group visited Antelope Canyon. Some of us opted to tour two different locations, one called rattlesnake canyon and the other upper antelope. Rattlesnake was quite tight and required scaling ladders to access the furthest reaches of the canyon. Upper antelope was much easier to negotiate but also was filled with many more people on tours.  I used the tour to try my hand at High Dynamic Range (HDR) photography. I have to say I am very excited about the results. The imge below is made up of seven individual images spanning 14 f/ stops.  Tuesday morning we returned to Horseshoe Bend and enjoyed much more favorable conditions. I presented my talk on color correction techniques in Adobe Photoshop CS4 on Tuesday afternoon. Wednesday finds us on our way to Bryce Canyon.

Antelope Canyon High Dynamic Range Image

Color Gamut & Fine Art Media

In conversations with my students and browsing the Internet, I find an abundance of worshippers who believe the holy grail of ink jet media is the one with the widest gamut. Choosing the very greatest gamut and forsaking all other considerations is certainly a choice that one can  make and perhaps someday compromises will not have to be made when setting sights on this goal.

I personally like the look and feel of fine art media for many of my prints and don’t want to avoid using it for the sake of greater gamut.  It is true that the gamut is an inherent property of the media for a given ink set and printer and there is nothing you can do to materially increase it.  That does not mean that you must accept the “flat” look or “lack of punch” that is often associated with the fine art media.

I have discussed this with many printers. They send their image to one of the wide gamut photographic papers and to a fine art paper and are terribly disappointed in the results on the fine art media. This is an unrealistic comparison because  the fine art media will definitely “:dumb down” the look of the print. It simply accepts ink differently. So there are two things going on in the fine art print, the smaller gamut and the distinctly different inking properties. I believe these two are lumped into one when the fine art media is dismissed out of hand.

There is a solution, and of course it does entail some more effort. The solution is to use the soft-proofing capabilities of Photoshop and to make further adjustments to your image before printing. These adjustments are specifically to accommodate the media you are printing to. While you are not improving the gamut of the media, you can return the “punch” that you saw on your monitor to the print. My experience is that soft-proof adjustments for  photographic media are usually minor but for fine art media they can be extensive. 

For me, I will give up a little gamut in my images for the look and feel of the fine art media. It is a compromise that I am willing to make. Perhaps down the road, it will not be necessary and I can have the widest gamut of all media.

Depth of Field Calculator for Your iPhone

Using depth of field as a creative tool in photography can make the diffenrece between a snap-shot and a photograph. Unfortuantely, the depth of field infromation that was once engraved on lens barrels has pretty much gone the way of the dinos in modern lenses. Instead the information is usually provided in tabular form with the instructions that are packed with the lens. You know, the piece of paper that often gets tossed out or lost.

There are several on-line depth of field calculators available but unless you are lugging your laptop with you along with your tripod and other gear, they really don’t help very much.  Enter the applications for the iPhone. An iTunes search will turn up several applications costing between $.99 and $3.99.

I really like the design of the f/8 DOF Calculator. It allows you to build a “camera” bag with the specific camera bodies and lenses that are part of your actual equipment. The camera body is simply selected from a drop down list. My Canon 1D MarkIII and D30 bodies were included. The lenses in your camera bag are created by specifying their maximum and minimum focal lengths, maximum aperture and closest focusing distance.

Main Display Page

Once entered, you simply select the body and lens combination you are using and use sliders to enter the data necessary to compute the depth of field. Buttons at the bottom of the main page let you select f/stop increments, distance units and scale. Everything you need to take advantage of depth  of field is calculated by this handy application.

Since I always have my iPhone with me things could not be more convenient.

Contrast Masking in Photoshop

In days long gone (at least they seem so),  creating cibachrome prints from chromes often required the use of a contrast mask to reduce the over-all contrast of the image.

Original Image as captured on chrome film.

Occasionally a digital image can benefit from applying a contrast mask. On a trip to Mexico several years ago I captured this image of Mexican children at a festival. It was high noon under a blazing sun and no fill flash. The resulting chrome was very contrasty.

Mimicking the contrast masking procedure used when making prints from cibachromes I first create a duplicate of the image in Photoshop (Image->Duplicate) and arrange a tiled view of the original and duplicate image. The duplicate image is then converted to a grayscale.  (Image->Mode->Grayscale). The resulted is shown in Step 1.

STEP 1 The image has been duplicated and the duplicate converted to a grayscale.

 
Step 2 inverts the grayscale to comlpete the creation of the contrast mask as seen below. (Image->Adjsutments->Invert)

Step 2 The duplicate image has been inveretd to complete the contraast mask.

Pin registration of the mask and the original is accomplished by selecting the inverted grayscale image and while holding down the shift key, dragging it onto the original. The result is shown in Step 3 below.

Step 3 The Inveretd grayscale image has been positoned as a layer over the original

Step 4 changes the blending mode of the contrast mask from normal to overlay resulting in the effect of applying the contrast mask as shown below.

Step 4 The contrast mask has been applied to the contrasty image

The last step is to adjsut the opacity of the contarst mask layer to create a pleasing result. My final choice for this image was 86%. Below are the before and after images.

Original Image as captured on chrome film.

Final after applying the contrast mask and adjsuting the opacity of the contrats mask layer

Image Resolution and Image Size

The question I get asked more often than any other in my digital imaging and Photoshop classes is “How big can I make a print from a file from my digital camera?” I will answer the question specifically, but first consider the factors that influence the answer to the question.

Native Resolution: This is the actual capture resolution whether by scanner or camera sensor. It is sometimes represented by file size, but specifying in terms of mega-pixels or pixel dimensions is more intuitive. In general, the greater the native resolution, the larger the size of the final printed image can be. However, it is important to note that camera sensors of the same pixel dimensions (resolution) do not necessarily yield images of the same quality. For example, sensors of smaller physical size will be more susceptible to noise than larger sensors with the same mega-pixel resolution.

Image quality: For a given “native resolution” the better the quality of the image, the more tolerant it will be to “up-sizing”. In many respects this is no different than the film world when the quality of the negative had much to do with how much enlargement the image could tolerate. Image quality depends on the quality of the equipment used to capture it, proper exposure, camera steadiness and the photographer’s technique.

Viewing distance:The distance at which a given image is viewed influences what the acceptable print resolution can be. In general, photographic prints in the traditional sizes of 8×10 to say 16×20 are viewed at roughly arm’s length or about three feet. Much larger images (panoramas often may fall into this category) are usually viewed from greater distances and may be rendered at a lower image resolution than the smaller ones.

Care in post-capture processing of the image: Even a high quality native image can be rendered unsuitable for large size prints by poor techniques durng post-capture processing. Techniques include such standards as tonal range adjustment, resizing and sharpening.

Viewer discernment: The judgment of photographic quality is truly in the eye of the beholder. For this reason alone, there is no universally accepted definition of an image resolution that equates to photographic quality. I have demonstrated this in my classes. I have shown prints of image resolutions from 180 ppi to 340 ppi. Seen individually, most students stated that they found the images of “photo” quality. However, when they see the prints together, they can easily distinguish between the one printed from the highest image resolution and the one printed from the lowest. In some cases, they can even put them in the correct order of increasing image resolution.

Image subject: This also is subjective, but the subject matter portrayed in the image can determine how large it can be printed. For example, still life photographs portrayed in an “arty” way, can sustain a greater degree of enlargement than images where the expectation of fine detail will require greater image resolution.

Media: The media used for printing can have a strong influence on the size a given digital image can be printed to. For instance, I have seen images printed on highly textured canvas that look wonderful, but fail when printed on a glossy photo paper or fine art media.

So there you have it; a lengthy list of considerations that impact the answer to the question of how large a print can be made from a given “native capture”. Now let’s talk some specifics.

Camera resolution required to make common print sizes as a function of image resolution

The data in the table presents a pretty discouraging picture. It is often claimed that image resolution must be 300 dpi to achieve “photo quality”. Does that really mean that we can only print to an 8″ x 12″ with an 8.3 Mega pixel camera such as the Canon30d as the above table suggests? In my experience, certainly it does not. I routinely print images from a Canon 30d to 16×24 and, on occasion, even larger. This is where all of the factors I listed above come in to play. For instance, I have settled on 240 dpi as my standard for most of my digital images from the Canon 30D, this allows me to print up to 9.7×14.6 without interpolation (ie using the native capture).

In addition, I have found that if the original image is of high quality and I take care in post-processing, that I can up-size or interpolate using Adobe Photoshop so that the final image size is 2 to 2.5 times the native size or in the case of my Canon30d, up to 24×36. In fact I prefer these images to those from my chromes scanned at 3600dpi and printed to the same final print size. So, the numbers in the table don’t present such a discouraging picture after all!

To determine your own “comfortable” image resolution, I suggest you select one of your best digital images. Judge it by critically inspecting it at 100% in Photoshop. Print that image using several different image resolutions withoutinterpolation. Compare the images and select the resolution that satisfies your expectation of image quality. Once you have selected your personal image resolution, print the same image up-sized. Try up sizing in the range of 1.5x to 2.5x using Adobe for the interpolation. Compare the up-sized images to establish your personal limits for image up-sizing.

Determining your personal working image resolution and up-sizing limits is exercising one of the exciting aspects of digital imaging: ultimately you are in complete control of the resulting image and have no one to satisfy but yourself.