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Magic Wand Selections
Printer Resolution
Screen Frequency
File Size

Magic Wand Selections

If you need to select a complicated image that is sitting on a simple background, if is often easier to select the background (using the Magic Wand) and then choose Select > Inverse to get the subject. The magic wand is used to select the same colour pixels on a layer. It is a fast selection tool only and is not used for truly accurate methods of selection. The best way to select an accurate and sharp shape is to use Paths. This is explained on another page as Path's can be quite involved.
However, using the Magic Wand to select parts of the layer is very handy. You can also adjust the tolerance of the pixel selection (colour selection). Click on the Magic Wand Tool, on the top of your screen, you can manipulate the tolerance of colour (pixels of the same value or close to same value). By adjusting the different tolerances, you can reasonably make quick selections of you image.
TIP: Develop a skill of Inverse. This means, that when you use the Magic Wand, It selects the pixels in Positive format, for a live example and understanding, use the Magic Wand on any part of a file you have open now.
Then, on the top menu bar, Choose > Select > Inverse.
You can see that the selection has been flipped into a negative selection. This is very handy for actually keeping what the Magic Tool Selected in the first place for you.
Other TIPS: Develop a skill of using the Modify Functions found in the top menu. Choose > Select > Modify > Expand. Type in a new pixel range that the selection will expand by. In this manner, when you use the Magic Wand or any other way of creating a selected part of your layer, you can increase or decrease the selection path by any number of pixels. Very handy when the Magic Wand Tool doesnt quite get it close.

Printer resolution

The number of ink dots per inch (dpi) produced by all laser printers, including image setters and digital printing equipment. Most desktop laser printers have a resolution of 600 dpi, and image setters and wide format printing machines have a resolution of 360, 720, 1200, 1440 dpi or higher. To determine the appropriate resolution for your image when printing to any laser printer, but especially to image setters, see "screen frequency."

Ink jet printers produce a microscopic spray of ink, not actual dots; however, most ink jet printers have an approximate resolution of 300 to 720 dpi. To determine your printer's optimal resolution, check your printer documentation. You can quickly change the print setting in Photoshop by choosing > Edit > Preferences > Units and Rulers > Print Resolution For New Documents.

Or

Choose > File > Page Setup > Printer > Use the options your desktop or wide format printing equipment allows.

Screen frequency

The number of printer dots or halftone cells per inch used to print grayscale images or color separations. Also known as screen ruling or line screen, screen frequency is measured in lines per inch (lpi)--or lines of cells per inch in a halftone screen.

The relationship between image resolution and screen frequency determines the quality of detail in the printed image. To produce a halftone image of the highest quality, you generally use an image resolution that is from 1.5 to at most 2 times the screen frequency. But with some images and output devices, a lower resolution can produce good results.

File size

The digital size of an image, measured in kilobytes (K), megabytes (MB), or gigabytes (GB). File size is proportional to the pixel dimensions of the image. Images with more pixels may produce more detail at a given printed size, but they require more disk space to store and may be slower to edit and print. For instance, a 1-by-1-inch, 200-ppi image contains four times as many pixels as a 1-by-1-inch, 100-ppi image and so has four times the file size. Image resolution thus becomes a compromise between image quality (capturing all the data you need) and file size.

Another factor that affects file size is file format--due to varying compression methods used by GIF, JPEG, and PNG file formats, file sizes can vary considerably for the same pixel dimensions. Similarly, color bit-depth and the number of layers and channels in an image affect file size.

Photoshop supports a maximum file size of 2 GB and maximum pixel dimensions of 30,000 by 30,000 pixels per image. This restriction places limits on the print size and resolution available to an image.

If your working on very large file sizes, you may also be interested in ready the topic 'Using Photoshop With Large Files'.

Cropping Images to size

With the Crop Tool selected, Click and Drag over the image.
Release when you've selected the part of the image you want to keep. Don't worry about getting it just right, you can always go back and edit it.

You will have a dashed line with little squares (selection handles) around the dashed line. This enables you to edit the selection by mousing over them and dragging in either direction to enlarge or decrease your selection.

By default, Photoshop will mask out the area that is not part of the selection. You can turn this on or off by going up top to the Options Bar and selecting/deselecting Shield Cropped Area.

To rotate move your cursor over one of the 4 corners until you see it change into a double sided arrow.

Cropping Images to specific size

Better to use the guidelines or use 'fixed size' options in your Marquee selections tools.
TIP: When using the fixed size option selection tool, type the value including the following code:
EG: '120px' or 120cm or 120in in the width and height fields. The result will actually look like 120 px or 120 cm. Do not add a space when entering the amount, Photoshop will complete this automatically. Also works when manipulating HTML.
Then when the section of your image is selected, cut and paste into a new file. Your image will be specific in size and output.

Increase your canvas size relatively

The next time you have to increase the size of your canvas, check out Photoshop's Relative option. Just choose Image > Canvas Size. Then, in the resulting Canvas Size dialog box, select the Relative check box. Now, just enter the how much space you want added to the Width and Height text boxes. (this avoids creating documents with random sizes).

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