Photoshop: Color and Image

Topics: Color, Pixel, RGB color model Pages: 10 (3200 words) Published: September 25, 2009
Basic concepts and terminology
The Photoshop is a tool for photograph retouching, enhancing and will give you flexible features to produce stunning images which can be put in Web pages. If you have not fully understood the coloring of your images, you have go through the chapter on Basic Concepts. Basic Concepts

What is computer graphics? There are two main types of computer graphics- vector and raster images. Vector images, such as those created in Adobe Illustrator, are made up of mathematically defined lines and curves called vectors. Raster images, such as those created in Adobe Photoshop, consist of a grid, or raster, of small squares, known as pixels. Several types of resolutions are important when working with digitized images. They are: Image resolution refers to the spacing of pixels in the images and is measured in pixels per inch (ppi). If an image has a resolution of 72 ppi, this will have 5184 pixels in a square inch. Pixel depth (bit resolution) is a measurement of the number of bits of stored information per pixel. Bit resolution determines how much color information is available for each pixel. Greater pixel depth means more available colors and more accurate color representation in the digital image. E.g. A pixel with a bit depth of 8 has 2**8, or 256 possible values (colors); and a pixel with a bit depth of 24 has 2**24 or 16 million, possible values (colors). Monitor resolution defines the number of dots or pixels per unit length of output. It is measured in dots per inch (dpi). The device resolution for a Macintosh monitor is typically 72 dpi. Screen frequency, also known as screen ruling, refers to the number of halftone cells per inch in the halftone screen used to print grayscale image or color separation. Screen frequency is measured in lines per inch. Output resolution refers to the number of dots per inch (dpi) that output device, such as a laser printer reduces.

Image fundamentals:
• Bitmapped image as a mosaic made out of square tiles of various colors. • Images are colored pixels displayed on screen. When enlarged, they look like unrelated collection of colored squares. After reducing, these blend together to form an image that looks like a standard photograph. Image size and image resolution:

• Image size refers to physical dimension of an image; image resolution is the number of pixels per linear inch. For example, if the resolution of an image is 72 ppi(pixels per inch) - you get 5,184 pixels per square inch. Image creation, duplication and save:

• Open existing images in CD-ROM or hard disk, use File->Open. • Creating a new image, choose File->New to bring up new dialog box. If the Clipboard contains an image, the Width, Height and Resolution option boxes shows the size and resolution of that image. [pic]

•  Otherwise, you can enter your own values in one of five units of measurement: pixels, inches, centimeters, picas, columns or points. (A pica, incidentally, is equal to roughly 1/6 inch and a point is 1/12 pica, or roughly 1/72 inch). •  Creating a new image from scanner, use File->Acquire->Scan. •  Creating an image from the Clipboard, use Edit->Paste. •  Duplicating an image by choosing Image >Duplicate: This is important when you try out an effect without permanently damaging the original image on disk. •  Saving an image on disk by choosing File >Save and this will display Save dialog box, prompting for the name of the image, specify its location on disk, and select its file format. •  Saved file formats can be up to 22 types from its open and save dialog boxes. It can support more through the addition of plug-in modules. Here are some descriptions of the supported file formats. [pic]

Scanning, importing and exporting
To scan images, use Acquire command in the File menu.
Determining the scan resolution depends on the capability of your output device. If the image is used on screen, the best is 96 ppi for PC...
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