GS-PS: Core Concepts for Image Quality

Review

• Menu Bar
• Status Bar
• Pallets
• Tool Bar
• Image Window
• Zoom Tool
• Hand Tool

Navigator Pallet + Hand Tool

• When using another tool, you can press the spacebar to temporarily access the hand tool. You can then drag to move around the image. When you stop pressing the spacebar,  you will return to using the other tool.
• To zoom and move around the image with the Navigator palette, choose Window>Show Navigator. The navigator palette will appear:

Use the navigator palette to zoom in or out of an image (by dragging the navigator slider) or to move around the image by dragging the view box (when you are zoomed in). The view box (red box in the above example) shows the part of the image that is currently being displayed in the main image window.

JPEG's vs. RAW vs. .PSD's

• Always try to take images in RAW format if you camera allows it.
• If you have a RAW image, you can do some editing before you import the image, then save the file as a .psd
• If you have a .jpg/.jpeg, you should immediately save it as a .psd before doing anything else.

Correcting mistakes and History Palette

• Choose Edit-Step Backward to undo your last action.
• Choose Window-Show History to view the History palette. Then you can click on a previous history state to undo one or more of your actions.
• Choose File-Revert to return to last saved version of file.

Getting Help

To access online help, choose Help > Photoshop Help.

Image Size

• Digital images are made up of pixels (picture elements), which can be defined as colored squares. Each pixel is only one color.
• A good way to learn about image size, resolution, and print size is to experiment with an image using the Image Size dialog box.  To do this, open an image in Photoshop. Then choose Image > Image Size, and the Image Size dialog box appears.
• 
• Under Pixel Dimensions, Width and Height refer to the number of pixels in an image, which has to do with the size of display on screen.
• Under Document Size, Width and Height refer to the size of the image when printed.

Experimenting with Document Size Options

• Uncheck Resample Image and change the resolution to 300 ppi. (high quality printing)  
• Note what happens to your document size numbers
• To change the print size of an image, uncheck the "Resample Image" box.  When you turn resampling off, notice that the Pixel Dimensions are no longer editable.
• Under Document Size, there is a trade off between Width/Height and the Resolution. If you increase the width and height, resolution decreases. If you increase the resolution, width and height decrease. 
• As a general guideline, newsletters and newspapers are likely to require resolutions in the range of 150 to 200 ppi, and magazines are likely to prefer high resolution images of 250 ppi or more. 
• A resolution of more than 300 ppi may be unnecessary. But keep in mind that if you crop the image and then enlarge the cropped image to the size of the original, the resolution will be lower than the original... so an image that was 300 ppi, then cropped and enlarged, may then be much less than 300 ppi.

Color Modes

• In Photoshop, you are always working in a color mode. The default mode is RGB (Red-Green-Blue), which is also the default mode for the Web. If you are only working to create color images for the Web or for a desktop inkjet printer, you may not need to use any of the other modes. But it is useful to know about modes because this gives you a better idea of how Photoshop creates, displays and prints images.
• Each color mode defines the colors that combine to make up the color of every pixel in the image. To change color modes, choose Image > Mode.
• Color modes are made up of channels. Each channel is a grayscale image. A grayscale image is an image made up of shades of brightness (as many as 256 shades, from white to black). To view the channels, choose Window > Channels, and the Channels palette will appear. Modes with fewer channels result in smaller file sizes.
• For example, in RGB mode, the red channel is a grayscale image made up of brightness values for the color red; the green channel is made up of brightness values for the color green; and the blue channel is made up of brightness values for the color blue. Each pixel in the full color image is made up of a combination of of brightness values for red, green, and blue.
• Note: It is possible to edit an individual channel, which is useful to improve the quality of some images.

Some of the most frequently used color modes are:

RGB mode three channels (Red, Green, and Blue) used by all monitors and by the Web recommended by Adobe for editing color images

Grayscale mode One channel, 256 shades of gray

Bitmap mode black and white (no shades of gray) used for line art

Indexed mode one color channel, up to 256 color values used for GIF images destined for the Web

CMYK mode

• four channels (Cyan, Magenta, Yellow, Black)
• used by professional printing houses. If you are producing a images for a publication or poster, you may need to save it in CMYK mode.

Core Concepts for Photoshop

1.  .psd is lossless.  .jpg is lossy.  Always convert jpg's to .psd's before doing anything
2. create a new (duplicate) layer before you get started by dragging the background layer to the New Layer icon.  You can then poke out the eyeballs of the background layer and get to work
3. Always create Adjustment Layers, don't adjust the image itself
4. Print/export from the .psd file, if possible, don't convert to another file format unless necessary.  And, if you have to, do it last
5. Create "Comps" as you go for states that you like - layers/layer options/edits... frozen