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NZ Macguide Issue 10
Most of us are happy that digital photography and Mac computers require so little effort to use. However, some of us want to get as much from the photographic experience as possible. 'White balance' was something I practically ignored until I started researching this article. Once I saw the huge differences possible in the final image, I changed my mind.
What exactly does white balance do? Sunlight is the gauge; our brain automatically registers light as white, no matter what the source. Most artificial light has a colour cast, e.g. household lights are yellow, and fluorescents are green. White balance is normally associated with video cameras. When using conventional film you can use filters or special film types to compensate for these irregularities. In fact, digital video cameras have filters to adjust light to the right colour and digital still cameras, like their video cousins, simplify things for you by automatically adjusting these filters (red and blue) to give the correct white balance without your input.
Using flash has the benefit of adding 'white' light, and this is the obvious way to correct indoor lighting. When the light level becomes too low the camera will automatically fire the flash - but sometimes you don't want to use flash.
So why fool with the white balance? If you take a shot without adjusting the white balance you will get an acceptable image that can be corrected on your Mac if need be. If you take a white balance reading first, the image will be totally different - the colour will look more natural. Essentially you'll want to do it when you use exposures longer than about one second. Most of today's digital cameras give you a simple override for various lighting situations. In your menu will be settings for fluorescents, overcast, household bulbs and sunlight. If the image doesn't look satisfactory after using an automatic white balance reading, try using one of the pre-sets.
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Shots of Oriental Parade, Wellington, taken from the balcony of the Quality Inn with an Olympus C-5050 demonstrate the difference you will get by attending to white balance. The shot using auto white balance looks a little warm (yellow), with good shadow detail and clean white trails of light from the car headlights. However, accessing the camera's menu and taking a custom white balance reading gives the image clean whites (look at the pedestrian crossing) and renders the road surface a more natural colour.
The correct way to take a custom white balance reading is to use a white piece of paper. Photocopy paper is fine. Hold it in front of the camera and take the reading from the paper. If you carry a small notebook check to see if it has an un-ruled page, and use this to take your white balance reading.
Noise and compositing
Noise - it's not restricted to the loud car stereo in the hatchback of that spotty boy who's dating your daughter. Digital cameras suffer from a phenomenon called 'noise': a speckling of white throughout the image that occurs in long exposures. Not all digital cameras include a feature for controlling this, but more manufacturers are doing so. Search the camera's menu for 'noise reduction', and turn it on to help eliminate those annoying white speckles (on the Olympus cameras this increases the time it takes to write the image).
I shot images at dusk from Te Mata Peak - looking down over Havelock North and Hastings - to get detail in the foreground and some vehicle light trails.
Using a tripod and a cable release is a must for these long exposures. The shot taken with the camera set to Auto White Balance' provides an acceptable image, though there's a little red in the grass and rock areas in the foreground and a cool blue - as you would expect - in the city part of the scene.
The great thing with digitals is that you can review your images immediately and make any necessary adjustments. So, working quickly in the fading light I accessed the menu and took a custom white balance reading, then fired the camera with the supplied remote control. With two images shot in the same place on a tripod it is easy to merge the two, and salvage the best components from each. Take them to the chop shop - Photoshop! Inside Adobe Photoshop 7 is a feature called a 'layer mask' that allows the image below the top image to be exposed. By 'brushing' either black to reveal the layer below, or white to replace it with the original, you can quickly hide errors you have made on one layer with better features from another.
You need to open two images that are the same, and drag one image on top of the other (or Select All in one, choose copy, select the second image and choose Paste). Save and name this new file something different from the original file name. This ensures you don't lose the original image. Make a selection of the two main areas, in this case the city and the peak. Using the rectangular marquee tool, select the major part of the section of the image you are selecting. Choose - Select, Inverse and Inverse the Selection.
Next add to this selection by using the Quickmask; the original rectangle selection will appear pink. Choose a brush and paint in the rest of your selection along the hills. This may take some time, and it pays to blow the image up to 200 per cent to get the most detail.
Don't panic if you go over a line as you can revert to the standard mode, invert again, and then use the Quickmask setting to paint out the botched selection. Use the brackets to toggle up and down the range of brushes (this works on both PCs and Macs). Once you have the selection you want, go Select, 'Save Selection, and a new window appears with the option Channel and New. Name this new channel.
(With the peak shot I made a channel of the peak and a separate one for the city by saving one selection, then inverting and saving this selection.)
By having the two selections you can recall each selection by choosing Select, Load Selection, use the drop down box and choose which one you want. This allows you to do different things to the independent layers and selections. It's also handy if at a later date you wish to use different parts of the image for another image. In this case I could remove the city and replace it with a shot of some boiling lava.
I've chosen to reveal some of the bluer layer from below my almost perfect top layer by using a layer mask. This is a great method, and an easy one to perfect. Choose the top layer and add a layer mask.
Go to Select, load selection and pick city lights. Go to the palette and single out the gradient tool. If it's not visible, it is hidden under the paint bucket tool. Make sure white is the top colour and black is the background colour.
Drag a line from just below the selection to almost the top of the picture. In the layer mask you will see the gradient tool, and how it moves along the selection. If it still needs work, choose Edit, Undo gradient tool and Redo. You can tell you have selected the layer mask, as a little box with a circle will appear to the left of the image in the layers palette. If the image is selected there will be a little paintbrush in this box. Practice flipping from the image to the layer mask to get familiar with the two symbols.
You should now see the merging of the two layers in my photo. The sky has taken on the darkness of the lower layer and - having used the gradient tool - the lower layer subtly merges into the upper one. Use layer masks whenever you wish to work quickly - they can hide a multitude of sins.
The original files are juicy 15meg TIFFs, images like this from a five mega pixel can be blown up really big! I've printed the final image out to A3 size, and it looks fantastic.
© Parkside Media 2004
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