Dodge, Burn and Sponge, the Photoshop CS4 Way
The improvements in Photoshop CS4 come in all shapes and sizes — some big and obvious, and others are important yet easy to miss. The improvements in the Dodge, Burn and Sponge tools fall into this latter group.
By way of explaining what I mean, let me start with an overview of what these tools do, then we'll be in a better position to explain how Adobe has improved them in Photoshop CS4.
Dodging and burning simulate tools from the traditional film darkroom to modify the exposure over potions of a print. To dodge a print, a piece of cardboard or even the hand of the person doing the developing is use used to block the light source and thereby develop that section less than the rest of the print. This has the effect of leaving it lighter than the surrounding areas and is usually done to preserve more detail in shadow areas. Burning is just the opposite. After the standard amount of time has elapsed to develop the print as a whole, additional light is focused in on areas to darken them in the final print. Although Photoshop doesn't work the way traditional darkroom chemistry does, the Dodge and Burn tools produce a similar effect and serve as convenient ways to selectively lighten or darken portions of an image.
Oregon's Mt. Hood as shot
Dodge and Sponge problems in previous versions of Photoshop. The sponge oversaturated the mountain peak while dodging the tree line left it washed out and fake looking.
Dodging with 'Protect Tones' still revealed some detail in the trees and the 'Vibrance' option of the sponge tool worked much better to emphasize the warm glow on Mt. Hood.
The Sponge tool comes to Photoshop by way of watercolor painting where an actual sponge is sometimes used to soak up some of the paint in order to modify how much color remains in part of a painting. The sponge tool in Photoshop similarly can be used to desaturate (or saturate) the color where it is applied to an image.
Although these tools in Photoshop are indeed convenient, they aren't perfect. Dodge and Burn tend to lighten and darken indiscriminately where they are applied, and the Sponge tool tends to saturate or desaturate equally indiscriminately where used. If you aren't careful, you can end up doing more harm to an image than good when using them. They can be used to good effect, but it's been all too easy for them to be overused. Photoshop CS4 addresses this problem quite effectively.
Accessing the Dodge, Burn and Sponge tools is still done the same way. You'll find them sharing one of the boxes in the tools palette on the left-hand side of the Photoshop main window. Clicking on whichever one is showing in the palette and dragging your mouse to the right will reveal the other two. After picking whichever one you need, you can fine tune what it does by means of the Options bar along the top of the Photoshop window. The options for all three are similar and are shown here. What's new in Photoshop CS4 is the checkbox at the end of each. In the options for Dodge and Burn, there's now a checkbox "Protect Tones" and in the Sponge tool you'll find a checkbox for "Vibrance." Each of these is checked by default, and for good reason.
"Protect Tones" is particularly helpful when dodging and prevents problems with haloing and washed out colors. In previous versions of Photoshop, it was all too easy to end up with areas that looked like they had been bleached when all you were trying to do was lighten up some of the shadows to show more detail. The same thing could happen when burning an area too darken it too but less often. Instead of lighter colored halos and washed out color though you could end up with black fringe halos and oversaturated colors. Checking "Protect Tones" tells Photoshop to use a new, more sophisticated algorithm when dodging and burning to allow you to better control brightness without such artifacts.
The "Vibrance" checkbox performs a similar improvement when using the Sponge tool. Previous versions of Photoshop saturated or desaturated all pixels equally to which the Sponge was applied. As you might have guessed, checking "Vibrance" tells Photoshop to use the same vibrance algorithm recently added to Camera Raw and Lightroom instead of the traditional method of changing saturation. Rather than raising or lowering saturation an equal amount for all pixels, vibrance affects areas of an image proportionally to how much they need it. Areas that are already fairly well saturated get affected less than pixels that could benefit more. This means you can paint with the Sponge tool over part of an image without having to worry about garish oversaturation nearly as much as in previous versions of Photoshop.
CS4 makes it easy to get good results with the Dodge, Burn and Sponge tools. They still operate directly on the pixels of an image rather than on a separate layer, but this just gives Adobe something to add to the next release of Photoshop. Progress marches on.