* Winter Wondering
* Changing Backgrounds
* Cropping Problems?
* Resampling For Size
Q) I live in Florida, but will be traveling to Yellowstone to snowmobile in January and I don’t know how my digital camera will react to the cold weather. What should I know, as I don’t want to lose any photos of this special trip?
A) Last year, I spent a couple of days with a digital camera on a dog-sledding trip in northern Minnesota, so I can speak from experience about shooting in cold weather. Aside from the usual warnings about keeping your camera away from moisture and dirt when shooting outdoors, there’s an additional concern with cold weather.
One word: power.
While your snowmobile may have plenty of power to get through the trip, digital cameras need a little more thought. The big enemy of batteries is temperature. They don’t like heat and they particularly don’t do well in cold temperatures.
Your batteries may last only a quarter of the time they usually work. It could be less or it could be more-in either case, I’d make certain that you have enough batteries between recharges.
There’s the option of an external battery pack that can be kept warm while connected by wire to the camera; some cameras have this as an optional accessory, plus there are some independent brands of external power packs. This is what I was able to use while mushing. It allowed me to keep the battery pack close to my body for warmth, which allowed for more shooting time.
It’s important to remember that you want to pay careful attention to your battery charge level while taking pictures. One way to corrupt the file system on a memory card is losing power while writing to it. While camera manufacturers try to safeguard writing to media, all bets are off when a battery is at its lowest charge level. If the camera runs out of juice at the critical time when the media card’s file directory table is being written to, you could lose or damage some of the data on the card. So replace the battery when the camera warns you, and in cold weather, don’t think you can take one more shot before swapping because the battery’s power can diminish quite quickly.
Another suggestion is to practice limiting the use of the LCD. This can help reduce battery drain.
And while I’m on the subject of practicing, there are some other things to think about when you’re heading out into cold weather.
Have you ever operated your camera while wearing heavy gloves or mittens? Go to an outdoor clothing store and bring along your camera. It also helps to try using your camera while wearing those gloves. If you practice in Florida where it’s warm, you’ll have a better chance for success in Yellowstone.
You might also want to make sure that you’re familiar with your camera’s exposure override settings. You’ll be around a lot of snow, which can drive the metering system in any camera crazy. If you have the time, when you arrive at Yellowstone, try taking pictures outside right away before you head out on the trails, and see how the images look. You might want to adjust the exposure settings accordingly.
Be very careful of moving a cold camera into warm conditions. This can cause major problems because of condensation, both on the outside and inside of the camera. Keep the camera in a zipped camera case or put it in a plastic bag until it warms up.
Also, with any outdoor conditions, make sure you bring something you can use to clean your lens.
Q) I’m looking for information on the use of chroma-key for backgrounds—why it’s used, and when to use the green and when to use the blue.
Roger E. Johnston Jr.
A) Chroma-keying is the process whereby all of the pixels of a certain color on one image are replaced with pixels on another image. If you’ve ever watched a weather report on television, you’ve seen a chroma-key. The meteorologist appears to be standing in front of a weather map, but, in reality, is standing in front of a colored background. By chroma-keying (keying on a certain color), the actual background behind the person is replaced by the map.
A chroma-key background is a solid, highly saturated surface that’s typically either blue or green in color. In the past, chroma-keying usually was relegated to moving images, namely video and motion pictures. As still-image-editing software has advanced, the chroma-key process has become available in the digital darkroom. You either can make use of the manual color selection in your image editor or use more sophisticated third-party tools to achieve good results (check out www.digitalanarchy.com).
The colors green and blue were originally chosen because they contrast with skin tones (which have a lot of red; if red was used, a person’s face would start to disappear as the color was replaced by the new image). Blue was preferred because of color spill on flesh tones. The blue spill could be removed with less objectionable color casting. Now the answer of green or blue usually is dependent on what color won’t be in the scene. In other words, if someone is wearing a blue shirt, you should use a green background so the shirt doesn’t disappear.
Here are a few tips to help you achieve a successful chroma-key:
• First, light the background evenly, top to bottom and left to right.
• Second, keep your foreground object as far away from the background as possible to minimize color spill.
• Third, light your foreground with the new background in mind. In other words, if you’re trying to key someone into a new background that has a window in the corner with the sun coming through it, it’s important that your foreground object be lit so it looks like the sun is shining in the same direction.
• Finally, when shooting, don’t use any diffusion on the lens (fog, mist, etc.). These filters will just mix the light and cause a bad key.
Q) I use an image-editing program to crop and make minor adjustments on some of my files. Does cropping just discard the extra pixels or does it actually recopy the file? In other words, does cropping create the possibility of artifacts degrading the image? I like to crop one side at a time, but I wouldn’t want to do it that way if cropping four times would increase the possibility of adding artifacts, rather than doing it in one pass.
A) As long as you stay in the “native” file format of your image-editing program or you use a TIFF file, you shouldn’t have problems with cropping one side at a time. A problem might occur if you open a JPEG file, crop one side, close the image as a JPEG, then reopen the file at a later time and crop another side and resave as a JPEG, and so forth. JPEG throws out data to compress files, then rebuilds that data later when the file is opened. Low levels of compression used only once have little effect on an image. However, multiple compression cycles (which happens every time a file is opened, then resaved) can degrade the image. In short, when working with compressed files, don’t keep resaving them in a compressed file format. All image-processing progr
ams work the same way concerning this issue.
Resampling For Size
Q) I would appreciate some help on resizing photos, particularly when to resample. Here’s a scenario: I upload an image from my camera, and Photoshop Elements shows the resolution at 72 pixels per inch. I want to print the image at 4×6 at 300 dpi. Where in the procedure would it be best to resample?
A) You can make the needed changes in one step. However, I like to do it in two parts, leaving the resampling (which is interpolation) off until the second part. I first make changes just to see how big an image I can get based on a desired printing resolution for the image of 200 to 300 ppi/dpi.
In other words, with resampling turned off (unchecked), I change the ppi/dpi of the image to 200 or 300 and see what the new image dimensions are. This lets me know if I have enough resolution in the original file to make my print. If I do, I use the appropriate resolution size without resampling because I don’t need to do any interpolation. If the image is larger or smaller than what I need, then I can size the image using interpolation, meaning checking the resample box. If you do resample an image to change its size, you’ll usually need to sharpen it slightly, too.
A final pointer: If you decide to redo the size of your image after you’ve already interpolated it once, start over with the original image. Avoid re-interpolating an image.
If you have any questions, please send them to HelpLine, PCPhoto Magazine, 12121 Wilshire Blvd., Ste. 1200, Los Angeles, CA 90025 or [email protected].