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Saturday, January 8, 2011

Adobe Photoshop: the basics

What is Photoshop?
Adobe Photoshop is image-editing software. It allows you to transform scanned photographs, slides and original artwork in many ways, for example, by cropping, rotation, resizing and by creating special effects using filters ranging in effect from blurring to mosaics.
Photoshop combines a full range of painting, editing and image composition tools, sophisticated selection tools, and methods for adjusting levels of grey and colour in continuous-tone images.

Lesson 1: Scanning, saving and set-up
To scan images into your computer, you need a scanner attached to your computer and scanning software installed onto your computer. Scanning software is supplied with the scanners, often Photoshop.  You can also buy Photoshop independently.
To scan a picture
  1. Place the original material on the scanner glass. It should be face-down. Your scanner manual will tell you which way round to put it.
  2. Launch the scanning software: Photoshop, Photo Deluxe, ScanWise, etc. If you already have Photoshop running, you can launch the scanning package from within Photoshop by choosing File > Import > and select the scanning package (eg ScanWise).
  3. Your software may automatically preview (scan) your document so that it appears on the right hand side of the scan window. If not, you will need to  click a Preview button to pre-scan the document.
  4. The scanning software will automatically select options for destination, image settings, file format, etc.
  5. You may change this if you wish from the buttons on the left hand side of the scan window.
  6. Click the Scan button.
  7. Save the image in the desired format (see page 7). If your scanning package was launched from within Photoshop, your image will automatically appear in a Photoshop window.

File size and resolution
Big is not always best: an A4-sized colour photo scanned at a resolution of 300 dots
per inch (dpi) takes up 28Mb! PostScript printing adds another 50% to the file size.
Where will you keep it? How will you transport it? Using a lower resolution reduces
the file size.  Set your resolution according to the end use of your image and output

  • Screen use (eg. web page): 72dpi
  • Posters, monochrome, line art: 100dpi
  • Colour printing in documents: 150dpi
  • High quality printing/microscope enlargements: 300dpi or higher
  • (to be continued)
Use RGB as your colour format unless you require colour separations at printing time
(in which case use CMYK).  CMYK is not available in Photoshop LE, a cutdown
version of Photoshop often supplied with scanners.
File formats
1 Photoshop (.psd): for “working” images in Photoshop
2 TIFF: for exporting to other printing applications.  (24bit colour, loss-less compression possible, channel masks saved).
3 PICT: for exporting to other printing applications (Mac only).
4 JPEG: for exporting tone-based web-images. Note, JPEG compresses the file
by losing file information so file cannot be reworked.
5 GIF: for exporting line-based web-images
6 PNG: emerging web standard to replace JPEG and GIF but not widely used yet.
6 EPS: encapsulated Postscript, for printing or inclusion in printed materials.

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