GDT 141&142: Photoshop

Handouts

Blending Modes

Blending modes affect how a tool or layer affects pixels on a lower layer. In these descriptions, “base color” refers to underlying pixels and “blend layer” is the layer for which a blending mode is chosen.

Normal
All base colors are modified.
Dissolve
Creates a chalky, dry brush texture in areas on the blend layer with partial transparency.
Multiply
A dark color on the blend layer darkens base colors that are lighter than that color.
Screen
A light blend layer removes the darker parts of the base color to produce a lighter, bleached base color.
Overlay
Multiplies dark areas and screens light base colors. Preserves luminosity.
Soft Light
Lightens the base color if the blend layer is light, darkens the base layer if the blend layer is dark. Preserves luminosity in the base color.
Hard Light
Screens the base color if the blend layer is light. Multiplies the base color if the blend layer is dark. Increases contrast in the base color.
Color Dodge
Lightens the base color where the blend layer color is light. Dark areas in the blend layer slightly tint the base color.
Color Burn
A dark blend layer color darkens the base color. A light blend layer color slightly tints the base color.
Darken
Base colors that are lighter than the blend color are modified, base colors that are darker are unaffected.
Lighten
Base colors that are darker than the blend color are modified, base colors that are lighter are unaffected.
Difference
Creates a color negative affect on the base color when the blend color is light. Produces noticeable color shifts.
Exclusion
Grays out the base color where the blend layer is dark. Inverts the base color where the blend color is light.
Hue
The blend layer’s hue is applied. Saturation and luminosity are preserved in the base color.
Saturation
The blend color’s saturation is applied. Hue and luminosity in the base color are preserved.
Color
The blend color’s saturation and hue are applied. Luminosity in the base color is preserved. Good for tinting.
Luminosity
The base color’s luminosity values are replaced by luminosity values from the blend layer. Hue and saturation are not affected on the base layer.

Basic File Operations Using Windows Explorer

Open Windows Explorer by clicking on the “Start” button at the lower left of the screen. Point to Programs, and choose Windows Explorer.

The frame on the left contains the directory structure of your computer. The desktop is the top level directory, or folder. Inside the desktop folder are My Computer and any other folders that are on the desktop. Next to the My Computer icon is a plus sign. To show the directories inside of My Computer, click on the plus sign and the directory structure will expand, showing the directories inside My Computer, and the plus sign will become a minus sign. To hide these directories, click on the minus sign. This applies all directories that have folders inside of them.

If you click on a directory on the left, the contents of that directory are shown in the frame on the right. If you were to click on My Computer, you would see not only all of the directories inside of My Computer, but also all of the individual files. To open a directory or file that is displayed in the right hand frame, double-click it.

There are several ways to transfer a file from your desktop to your Zip disk or to the server. The easiest way is as follows:

  1. Locate your files on the desktop that you wish to copy to the server or to your Zip disk. Make sure that you can see them behind Windows Explorer.
  2. In the left-hand frame of Windows Explorer, click on the plus sign to the left of My Computer. You will see several drives that you can access, including the H: drive (GDT141 on WC2...) and the Zip drive. If you are copying to a directory located on one of these drives, click its plus sign to reveal the directories inside of it.
  3. Still in the left-hand frame, click on the folder to which you wish to copy your files. The contents of that directory appear in the right-hand frame.
  4. On your desktop, click once on the file that you wish to copy, or drag a box around several files to highlight them all, drag it into the right-hand frame of Windows Explorer,and release the mouse button. Windows will copy files to external drives, such as the server or the Zip drive. Windows will move files between directories on local hard drives, rather than copying them.
  5. Once you see your files appear in the right-hand window, the file has been copied successfully.

An alternate way to accomplish this task is by using the Copy and Paste commands available in the toolbar of Windows Explorer.

  1. In the left-hand frame, find the directory that contains the file that you wish to copy. Click on the directory to show its content in the right-hand frame.
  2. In the right-hand frame, click once on the file, then click the Copy button in the toolbar located at the top of the window. You can also use the keyboard shortcut (Ctrl-C).
  3. Now, in the left-hand frame, find the directory to which you wish to copy your file. Click once on the folder to show its contents in the right-hand frame.
  4. Click the Paste button in the toolbar to paste the file that you copied into the selected directory. You can also use Ctrl-V.
  5. When you see your file in the right-hand frame, it has been successfully copied.

Raster Images and Bit Depth

Photoshop images are bitmap images, also called raster images. Bitmap images are composed of a geometric arrangement (a mapping) of dots. Each dot, called a pixel, represents a color or shade. On a computer, the arrangement of bitmap pixels is on a grid made up of squares.

Each pixel carries a certain amount of color information that is determined by its bit-depth. Color information, like all computer data, is made up of bits, which can have one of two values, zero or one. Bit-depth refers to the number of bits that are necessary to represent the total number of colors available to an image. To determine how many colors are available with a certain bit-depth, raise the number 2 to the power of the number of bits. For example, an image with eight-bit color can have 28 colors, or 256. An image with 24-bit color can have 16,777,216 colors. In RGB mode, Photoshop uses 24-bit color. Each pixel uses 24 bits, or 3 bytes (there are eight bits in a byte), of data to record color information. You can roughly determine the size of a file by multiplying the total number of pixels by the bit-depth of the image.

Image modes

Bitmap
Black and white only. An image must be converted first to grayscale mode and then to bitmap mode. Note: this is not the same as a bitmap file type.
Grayscale
Images are made up of 256 shades of gray, ranging from black to white. Records only luminosity values (darks and lights).
Indexed Color
Images are made up of any 256 colors. Photoshop creates a table, or index, of these colors, which you can view under Image>Mode>Color Table.
RGB
Images are made up of millions of colors composed of red, green, and blue, each with 256 different values. It’s the most versatile mode for working in Photoshop; every tool and option is available.
CMYK
Images are made up of millions of colors, broken down into cyan, magenta, yellow, and black. This is the standard mode for high quality print output.
Lab Color
Three-channel mode using lightness, green-to-red, and blue-to-yellow to record color information. It was developed to maintain color consistency between devices.
Duotone
A printing method that uses one or more colors to add tint to a grayscale image.
Multichannel
Images are composed of multiple grayscale channels for certain printing situations. RGB images converted to multichannel become CMY (cyan, magenta, and yellow, no black), and as a result lighten significantly.

Resolution

Resolution of an image is measured in pixels per inch (PPI). The higher the resolution, the more pixels there are packed into each inch. Standard monitor resolution is 72 pixels per inch, and the viewing size of individual pixels can never change without adjusting the resolution of your monitor.

All pixels in an image are the same size at any given time. However, pixels can be made larger or smaller, so an image with a fixed number of pixels can be made dimensionally bigger or smaller. The number of pixels per inch determines how big pixels are. By decreasing the number of pixels per inch (PPI), the pixels and the image become dimensionally bigger, but the image appears coarser. By increasing the PPI, the image gets sharper and dimensionally smaller.

In Photoshop, it is possible to resize an image by changing the resolution, or by maintaining the resolution and adding pixels to the image. Photoshop can resample an image to change its resolution and/or size by adding or deleting pixels. Resampling is necessary when you are increasing or decreasing in image’s size, but maintaining its resolution. To resize an image without resampling, uncheck the resample image box in the image size dialog box. As the image is resized, the total number of pixels remains the same, while the resolution changes. The file size (in k/MB) stays the same.

To resize an image by resampling, check the resample image box. Making an image larger with resampling yields a blurry image, because Photoshop adds pixels to the image by interpolation, or guessing. New pixels are added and colored by averaging the colors of the pixels on either side of the new one, which blurs any hard edges in the image. When increasing the image size, pixels are added and file size will increase. When making an image smaller with resampling, pixels are deleted and the file size decreases.

Output Resolution

The resolution for screen graphics (web and multimedia) is standard monitor resolution, or 72 PPI. The output resolution for print is based on the resolution of the halftone screen that the output device uses. Printing devices use a series of halftone dots that vary in size to simulate grays. In dark areas the dots are larger and closer together than in light areas. The resolution of halftone screens in measures in lines per inch (LPI). To determine the proper image resolution for a Photoshop image that is to be printed, multiply the LPI on the halftone screen by 1.5. For example, a printer that uses a screen with 133 LPI requires a Photoshop image with a resolution of approximately 200 PPI. To determine the proper resolution in the image size dialog box, click the “auto…” button and enter the LPI of the halftone screen. Photoshop will determine the proper resolution of the image.

Review for GDT 142 Final