1954 Ford Hood Ornament, Garden Grove, California, 2009.
Filter: Custom, RGB Swap + Discolor + Contrast. Original is chrome on a red hood.
CameraBag 2's main mission — low-fidelity toy-camera and retro looks — tends to involve a lot of color reassignment. Consequently, its collection of Adjust tools for manipulating color are extensive enough that they need an entire page of their own.
Color Channel Controls
The following tools allow you to adjust the behavior of the individual color channels (red, green, and blue). The Color Balance, Color Filter, and Color Corrector are mainly different interfaces for the same thing — level controls on the individual channels — and the R,G,B Curves tool is also related to those.
- Color Balance — separate level controls for each of the color channels.
- Color Filter — separate level controls for each of the color channels. This is the same functionality as Color Balance but with a slightly different interface. See details at the bottom of the Color Application section below.
- Color Corrector (in Color Filter mode) — separate level controls for each of the color channels, with a common response curve. See details at the bottom of the Color Application section below.
- R,G,B Curves — separate response curves for each of the color channels.
- RGB Swap — sets the output color for each of the color channels. See details below.
... the RGB Swap tool ...
The RGB Swap tool allows you to specify the coloration associated with of each of the color channels. You certainly can swap channels to get an unusual color effect, as was done in the hood ornament photo above. For monochrome, you can use RGB Swap as a channel mixer. But for color photos, the main reason to use RGB Swap is to emulate the color response or fading of a particular film type, by adjusting the redness, greenness, and blueness of the channels. Here's a table showing how the filters provided with CB2 use RGB Swap:
|Film NC01||Dull red||Aquamarine||Cornflower|
|Film NC02||Red||Olive green||Dark cornflower|
|Film NC05||Orange||Dark green||Deep blue|
The numerical values in the RGB Swap tool are not on an absolute scale of 0 to 255, although you certainly get that impression from the color pickers. Each is relative to all of the other numbers. It's all proportional, not just within an input channel but between input channels, too. That's not important for small tweaks, but it is for large shifts and re-assignments.
This can be especially useful when setting up a monochrome channel mixer, because you can use percentages directly in the fields. So if you wanted 50% green, 30% red, and 20% blue, you could set up the RGB Swap tool with values of 30/30/30, 50/50/50, and 20/20/20. There's no need to convert the numbers to be on the 0-to-255 scale. Then, if you decided you wanted more of the red channel, you could simply change it to, say, 40/40/40 and you don't need to go back and readjust the numbers on the other channels; they're automatically rebalanced for you.
CameraBag 2 provides a number of tools for applying a particular color to an image. Note that Color Corrector can do everything that Colorize, Tint, Dye, and Color Filter can do; those four tools just provide a simplified interface for simpler cases.
- Colorize — mixes the color with the image while generally retaining the brightness of the original pixels. The coloration tends to be more noticeable in the midtones and shadows. Whites are slightly colored, reducing their overall brightness. Mixing in a bright color can reduce contrast in the shadows because black pixels are replaced with the color. Use as dark a color as possible if you want to retain the shadows. Mixing in a white, gray, or black color has no effect.
- Tint — mixes the color with the image without concern for preserving the brightness of the original. At 100%, the image is completely replaced with the tint color. Contrast is reduced because the pixels are all moved closer to the brightness of the tint color.
- Dye — mixes the color with the image in a subtractive way, resulting in a somewhat darker image, usually with increased contrast. Mixing in a bright color will let highlights escape with minimal coloration while shadows are colored and deepened. CB2 uses this effect for its Dusklight filter. Mixing in a dark color will darken and color the highlights while blocking the shadows toward black, so use as bright a color as possible if you want to retain the shadows. Mixing in a white, gray, or black will remove all color and will reduce the brightness to have a maximum of the mixed-in color.
- Color Filter — a somewhat complex tool. See details below.
- Color Corrector — applies a color using any of the four modes above, but with the intensity of the effect depending on the brightness of each pixel according to a curve. The Colorize mode is the default, which seems a good choice since the Colorize mode is generally stable brightness-wise.
- Split Tone — applies different coloration to shadows and to highlights, using Tint mode. The color to be applied to each pixel is controlled by the brightness of that pixel (black=dark color, white=light color, others=in-between). When the Amount is set to 100%, all of the original coloration in the image is replaced, effectively forcing a conversion to monochrome. By selecting shades of gray for both shadows and highlights, the image can be converted to monochrome with a limited range; CB2's 1952 and Soft B&W filters do this.
- Color Correction — (hidden tool) applies different coloration to shadows, midtones, and highlights, in Colorize mode. There is no Amount control on this tool, so the only way to reduce its potency is by using desaturated colors. Color Correction cannot completely replace any existing color in the image.
- Discolor — applies a color to part of the image, using Color Filter mode (see details of Color Filter mode below).
... the Color Filter tool, Color Filter mode for Color Corrector, and Discolor ...
The Color Filter tool is flexible and calls for some finesse, by which I mean paying attention to (and perhaps directly entering) the numerical RGB values. Attempting to use Color Filter in a naïve fashion usually results in an effect rather like a weaker version of Tint.
The trick is choosing the correct RGB values. Values of 127.5 have no effect, 128 and above will lighten, and 127 and below will darken. If the color RGB is set to 127.5/127.5/127.5, the Color Filter tool has no effect at all. [Yes, the color controls can be set to fractional values, but the fraction won't stay displayed.]
With a true color filter, some of the light is removed so the overall image is somewhat darker. To emulate such a filter, none of the RGB values should be above 128. For example, a pure yellow filter might have values of 127.5/127.5/0.
The Color Filter tool, and the Color Corrector tool in Color Filter mode, can also be used for channel level control. They are essentially the same as the Color Balance tool, except that the ranges for each channel are denoted as 0 to 255 instead of -255 to 255, and the Color Corrector tool offers a response curve (the same curve is used for all three channels).
- Selective Saturation — increases or decreases saturation for a range of colors. Can also be used to produce the "B&W with selective color" look by desaturating the complementary color, as is done in CB2's filter called Red Splash.