Lecture 2 - Photoshop Basics.docx

5 Pages
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Department
Computer Science
Course Code
Computer Science 1033A/B
Professor
Vivi Tryphonopoulos

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Description
Photoshop Basics 4/20/2013 5:53:00 PM Lecture 2 Recap  All photo images (from camera, scanner) are bitmapped images (.jpg .gif .png)  Bitmapped images (Raster images): o Smallest unit of an image is the pixel (square) o Blocky when increase in size  Vector images: o Are scalable-will not be blocky if you increase or decrease size o Resolution independent – takes on resolution of output device o Vector images – based on a mathematical relationship, but are scalable, will not get blocky Images: Resizing Images vs. Resampling  To Change Image Dimensions: o Select Image> Size o Provides two measurements:  Pixel Dimensions  Document size Resampling (for Web)  You are physically changing the number of pixels in the image for the web, adding or taking away pixels  Pixel Dimensions = web o Width/height of our image in pixels  Width = 2048 Height=1536  Total # of pixels = 2048 x 1536 = 3,145,728 o To change simply type new values  Remember when going from smaller  larger dimensions you will get blurriness/pixilation  The higher the image dimensions to begin, the better the outcome  Downsampling – scaling it down o Decimation – eliminating pixels and therefore deleting information and detail from your image by averaging the values of source pixels contributing to each output pixel  Casts off unnecessary information by averaging together pairs of pixels or groups of pixels  Results in faithful tonality – image still looks smooth  Uses the bicubic sharper option***  Upsampling – scaling it up: o Interpolation – adding pixels by analyzing the colours of the original pixels and “manufacturing” new pixels which are then added to the existing ones  Guesses the values of the unknown pixels  6 interpolation methods:  Nearest neighbour:  Most basic/least sophisticated but fastest  Takes pixel color and assigns it to the new pixels that are created (uses the same color)  Poor quality, jaggedness  Bilinear:  Averages the color of the 4 pixels around it and performs simple linear calculations  Less jaggedness but still not good quality  Bicubic (default):  Averages the color of the 16 pixels, a larger sample size to draw from  Most sophisticated algorithm to give great results - most commonly used  Best for smooth gradients  Bicubic smoother:  Great for upsampling  Averages from more than 16 pixels  Adds a blurriness pass but great photos  Bicubic Sharper:  Good method for downsampling image  Decimation technique – eliminates by
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