|
DIGITAL PHOTOGRAPHY IN-CANYON John Hart Program in Atmospheric and Oceanic Sciences University of Colorado Boulder, CO 80302 nimbus.colorado.edu/hart/science.htm Sept 20, 2003
The Sony DSC-U60 is a small waterproof (to 5 feet) and rugged digital camera. In this Note I give examples of how this camera performed in the field, focusing on it's limitations and dealing with them. These problems are probably generic to most inexpensive digital cameras. Some defects can be correct after the shoot. Examples of post-processing, including level setting, histograms, and USM sharpening, are given. I do 3D photography, so I made a one pound twin rig. The cameras fire together (supposedly) and take left and right images that can be viewed in various ways in full stereo. Here is the rig.
Compare this with my previous 3D SLR-based camera which is big and bulky and weighs in at well over over 6 pounds.:
References on the DSC U60: Performance Tests, Preliminary Results Modifying the Cameras to Make the Stereo Rig (Camera Micro-surgery) Review by Professional Digital Photography Site or Another Review (gets "Good" image quality rating)
The Sony DSC U60 camera is incredibly small and light (8 ounces if you carry just one), water proof in pools and while swimming, and very easy to use. It seemed ideal for photography of water sports like kayaking, rafting, and canyoneering. Of course the image quality is not going to be as good as film, but you will get some shots you would surely miss with a big old film camera. The image quality is adequate for posting on the web, for digital projection, and for prints up to 4x6 or maybe 5x7. With a 128MB memory stick you can blast off 250 shots in a single day-trip, toss all the bad ones, and still come up with a load of winners. That's the equivalent of 8 rolls of film ($120 right there, for slide film with processing). And changing film in the mist of a waterfall is very nasty and takes a toll on SLR equipment. Most people will be interested in something like this for mono shooting. Of course then you only need one, and it's real handy. SO HOW DOES THE DSC U-60 PERFORM IN A REAL CANYON? Here is the good, the bad and the ugly. Click On a Thumbnail to see a larger view along with a description. THE GOOD AND THE BAD (but not awful) Nice Exposures and Pretty Sharp, Holds Detail in Brights and Shadows.... Care is needed in dark canyons - camera or subject movement can be a problem. Click On a Thumbnail to see 800x600 view along with a description. Note that these files are compressed for reasonable transfer speed on the web.
In summary, with uniform lighting (no hot spots or deep shadows), a steady hand, and folks that don't move fast (in the shade), one can obtain good pictures with this simple little digital camera.
THE UGLY (Difficult exposures exacerbated by limited dynamic range) Click On a Thumbnail to See 800x600 View along with a description.
The major problem with a low-end "consumer" digital camera is that the physical size of its CCD sensor is small. Small sensors have small photosites (pixels). This means that relatively few photons are received, especially in dark situations. Thus the "signal" for dark areas of a scene competes with the inherent quantum noise of the sensor as well as with the circuit noise of the camera's electronic systems. On miniature consumer digicameras, 12, 14, or 16 bit analog to digital conversion is not used, because the sensor doesn't warrant it (and it's more expensive than these little cameras' market price would support). Thus physically small sensors with high pixel counts typically suffer limited dynamic range and a relatively high noise floor that is compounded somewhat by simpler electronics and A-D resolution. In weak light, the camera compensates by turning up the analog gain to put the black level above the noise. But as a result of this excess gain, the whites, if bright enough, can overload the circuits and cause whiteout. In this situation the highlights lose all detail. As a result the major problem, as illustrated above, is burned out highlights. Careful scene selection (more so than with film or a high-end digital SLR) is one solution. EXPOSURE COMPENSATION IN THE FIELD Another annoying aspect was that while the camera did well on exposing bright scenes, it tended to over expose dim scenes. When a digital camera overexposes, the pixel elements tend to BLOOM over into adjacent pixels, causing loss of focus (resolution) and saturation.
(1) Mystery Canyon: Example of an overexposed dim (shaded) scene. Whites are burned out. Ferns are soft
(2) Best Photoshop adjustment of above image. Better, but whites are still gone and the image is still a tad soft.
(3) Same scene, but here I forced the camera to turn down its exposure by pointing it partially at the sky and using the exposure/focus preset. This locks in the exposure setting, which, after I point the camera at the scene I desire, produces a darker overall image. Now the image is sharper and the rocks have detail (compare with the first, unprocessed shot above). The shadows and dark areas are noisier (but so what). Much better overall.
(4) Now we adjust brightness and levels in Photoshop and apply some sharpening to the darker image. It works! Because there was detail originally, and no burned out whites, we end up with a much better picture!
Histogram of image (1). This shows number of pixels with brightness 0 (black as can be, on left) to 255 (washed out) on right. A good exposure covering the scene would have no spikes at 0 or 255. This is a poor exposure.
This is what I got for (3). By darkening the exposure I got rid of the 255 spike and didn't pick up any 0 spike. That's why it looked so good after post processing the level. The Sony DSC-U60 has no in-camera exposure correction setting buttons. The method of exposing on part of the bright sky isn't optimal. Ideally the decaying tail of the histogram on the right should be closer to the right (255) axis. But it still worked well. MORE POST PROCESSING
Here's another example with burned out highlights. There was no sky to point at to make the camera underexpose a little. I couldn't get close enough to the bright stone to use it to force an under-exposure. But by limiting the burnout to a small area of no significance (i.e. it's not at Ian's shirt, for example), I can save this image by post-processing it in Photoshop (or using some other image processing software like JASC Paint Shop Pro, which is a lot cheaper that Photoshop). The detail is gone from the bright patch, so just making it gray (by selecting it and turning down the brightness) won't help. But I can gently clone-brush in some stone detail, at a low level, from somewhere else. Releveling the scene, and applying a slight Unsharp Mask (USM) filter (80%, 1 pixel, 0 threshold) turns this into:
A lot better (and pretty good for a 2 MP camera in difficult light). Because the camera smooths low contrast areas (an undesirable artifact), it is best to use the 0 threshold in the USM filter. Sometimes, with a fully automatic camera, you get results you didn't anticipate (or have any control over). When the light is dim, the camera turns up its gain as much as it will (i.e. increases its effective ISO film rating), then takes a longer exposure to compensate for the low light. This will blur the image if there is any motion (of the camera or of the subject). But this can be a good thing:
Raw image.
Re-Leveled and sharpened (USM) in Photoshop. I held the camera steady enough that walls have detail. Blurred canyoneer conveys action.
Or even better. Here I was following the canyoneer and blurred the walls. Strong USM reveals the water splash well (great in 3D). CONCLUSIONS I will carry this lightweight stereo rig into rough wet situations. It would be nice if it had an exposure adjustment, but it doesn't. I will hope for uniform lighting (either bright or shady) and be aware of the dynamic range limitations of the camera. I will compensate in scenes that are not brightly lit, by aiming the camera at some brighter areas to force it to darken the exposure (while holding the preset button down). I will shoot lots of exposures this way, and check on the spot and delete (if needed) the duds. Being able to shoot hundreds of images in an outing makes it possible to capture action moments. You don't have to change film in the wet, and the small size is a blessing. It would be interesting to investigate other small compact "point and shoot" digital cameras for such activities. There are several miniaturized 5MP cameras on the market, but their sensors are also small, and so they probably will have the same dynamic range problems as the Sony DSC U60. On the other hand if a camera has the facility to make exposure adjustments, either by going to aperture or manual modes (if available, as in the Canon G5, Nikon 4300, Sony V1), or by making "exposure compensation" by changing the effective exposure value (EV), as in the small Sony P92/P10, then some of the bad shots I got with the Sony DSC U60 probably could have been saved. Though relatively small and light, these alternatives will need to be dry-bagged and handled with due care in wet environments. For photographing from the front of the raft, or while rapelling down waterfalls, it will be hard to beat the little U60. One just needs to be aware of its limitations.....
|
