Color Modes
Bit-depth
Bit depth specifies how much color information is available for each pixel in an image (bit per pixel). The more bits of information per pixel, the more available colors and more accurate color representation. Factor in the color mode's number of channels. # of bits per channel (bpc) = # bits per pixel divided by # of channels IE: RGB images with *8‑bits per channel* (bpc) are sometimes called *24‑bit images* (8 bits x 3 channels = 24 bits of data for each pixel) Higher bit-depth = more colors
Dithering
Dithering uses adjacent pixels of different colors to give the appearance of a third color. For example, a red color and a yellow color may dither in a mosaic pattern to produce the illusion of an orange color that the 8‑bit color panel doesn't contain.
Spot color
Spot colors are *special premixed inks* used instead of, or in addition to, the process color (CMYK) inks. Each spot color *requires its own plate on the press*. (Because a varnish requires a separate plate, it is considered a spot color, too.)
Color Lookup Table (CLUT
Stores and indexes colors in the image
Lab color mode
The CIE L a b color model is based on the *human perception of color*. The numeric values in Lab describe all the colors that a person with normal values sees. *Device-independent color model* Color management systems use Lab as a color reference to predictably transform a color from one color space to another. (L) lightness component: 0 to 100 (A) green-red axis & (B) blue-yellow axis: +127 to -128
Proof Setup command
Used to *simulate the effects of CMYK without changing the color mode* You should do this before transferring a file from Photoshop to InDesign (for printing).
Grayscale mode
Uses different shades of gray in an image. 8-bit images can be up to 256 shades of gray. Every pixel of a grayscale image has *brightness value* from "0" (black) to "255" (white). # of shades increases in 16 and 32-bit images. Can be measured as percentages of black ink coverage (0% = white, 100% = black).
Indexed Color mode
Produces *8-bit image files with up to 256 colors* When converting to Indexed Color, Photoshop builds a *"Color Lookup Table (CLUT)*. Program chooses the closest color, or uses *dithering* to simulate the color using available colors if a color in the image doesn't appear in the table. Palette and editing is *limited* Can reduce file size
Bitmap mode
*2 colors (black or white) to represent pixels in an image. Called "bitmapped 1-bit images" because they have a bit depth of 1 (bpc)
RGB mode
*3 channels: Red, Green, Blue*. Assigns an intensity value to each pixel. *Additive color model* Millions of colors. In an 8-bits-per-channel image, the intensity range is *"0" (black) to "255" (white)* 8-bpc images = 16.7 million colors/pixel (even more with 16-bpc and 32-bpc images) Used by computer monitors to display color. Standard color model Used in *web or email to reduce file size while maintaining color integrity*
CMYK mode
*CMYK: cyan, magenta, yellow, black* *4 printed colors* *Subtractive color model* Each pixel is assigned a *% value* of each of the process inks. The lightest (highlight) colors are assigned the small %, darker (shadow) colors have higher %. ie White = 0% across all four channels. *Used when preparing an image to be printed using process colors* You can use CMYK mode to directly work with CMYK images scanned or imported from high-end systems.
Converting images to Multichannel mode
- Layers are unsupported, therefore flattened - Color channels in the original image become *spot color channels* in converted image - CMYK -> Multichannel = C, M, Y, K, spot channels - RGB -> Multichannel = C, M, Y spot channels - Deleting a channel from an RGB, CMYK, or Lab image automatically converts image to Multichannel mode -> flattening layers To export a multichannel image, save it in *Photoshop DCS 2.0 format*
Spot channel
Can be added to add spot color plates for *printing*. Can also remove a color for printing.
Alpha channel
Component that determines *transparency settings* for certain colors or selections. Can be added to an image for storing and editing selections as masks.
Multichannel mode
Contain *256 levels of gray* in each channel. Used for *specialized printing* To export a multichannel image, save it in *Photoshop DCS 2.0 format*
Duotone mode
Creates monotone, duotone, tritone, and quadtrone *grayscale images* using *one to four custom inks*
Device-independent color model
Describes how a color looks rather than how much a particular color is needed for a device (ie monitor, camera) to produce colors.
Color Mode (or Image Mode)
Determines how colors combine based on the *number of channels* in a color model. Different color modes result in different levels of color detail and file size. 1. RGB mode (millions of colors) 2. CMYK mode (4 printed colors) 3. Index mode (256 colors) 4. Grayscale mode (256 grays) 5. Bitmap mode (2 colors - black and white)
Color channel
Every Photoshop image has one or more channels, each storing information about color elements in the image. The number of default color channels in an image depends on its color mode. By default, images in *Bitmap, Grayscale, Duotone*, and *Indexed Color mode* have *1 channel*; *RGB* and *Lab images* have *3*; and *CMYK* images have *4*. You can add channels to all image types except Bitmap mode images. Channels in color images are actually grayscale images that represent each of the color components of an image. For example, an RGB image has separate channels for red, green, and blues color values. Can add alpha channels and spot channels, too, on certain situations.
