Digital images and image compression

Transcription

1 BMS2062 Introduction to Bioinformatics Use of information technology and telecommunications in bioinformatics Topic 3: Digitised images and image compression Ros Gibson Digital images and image compression Overview What are digital images? Image types Image formats and compression Obtaining images Manipulating images Examples 2 What are digital images? The latest digital cameras combined with powerful computer software now offer image quality that is comparable with traditional film photography. Moreover, digital cameras are also easier to use and offer greater flexibility for image manipulation and storage. Stored on, and retrieved from digital medium such as disk, CD-ROM, DVD, digital tape, microfilm 3

2 Image types [1] 1. Line art / drawings / clip art 2. Photographs and photo-realistic images 3. Animations, simulations and morphs 4. Image Maps 4 Image types [2] Line art Computer art Clip art Icons 5 Image types [3] Photographs and photo-realistic images A photograph of Bacterial colonies on Agar (Presscott et al pg110) A computer-generated model of Reverse transcriptase and ribonuclese H. (Presscott et al pg376) 6

3 Image types [4] Animations, morphs and simulations Use multiple images Usually no sound Usually made from images not photographs 7 Image types [5] Image maps Used for: Web navigation Instruction Based on x, y coordinates Some html authoring tools have an inbuilt image map creator. The Microbe Zoo example of an image map 8 Image formats Consider: Orientation Colour depth Compression File size And consider these before creating numerous images get the specifications right first. 9

4 Format: orientation Portrait Landscape 10 Format: Colour depth Depth - max. # of colours 1 bit bit 16 8 bit bit 65 thousand 24 bit 16 million 11 Image compression Compression algorithm Resolution File size Compressed images lose quality each time they are edited. 12

5 Compression: algorithms.bmp (<= 16million colours or 24 bit colour, no compression).jpg (<= 16million colours or 24 bit colour, highly compressed).gif (<= 256 colour or 8 bit colour, moderately compressed) 13 Compression: resolution Resolution is the most important factor in digital imaging where fine details are required Pixels - picture elements, millions of these tiny squares are what make up digital images. The more pixels, the higher the resolution and therefore the better the quality of the image Dimension relates to the size of the image Screen size x 480 pixels, 800 x 600 pixels, 1024 x 768 pixels 14 15

6 Compression: file size Effected by width and height of image in the file colour depth compression format Uncompressed files are large than the same file that has been compressed BMP - 263KB JPG - 21KB GIF - 69KB 16 Obtaining images Off-the shelf (CDROM or Web page) Off a Web page Create your own Screen shots / dumps or capture Scan (least favoured) Digital photography - copyright 17 Obtaining images: Off the shelf Commercial CDROMS Web

7 Obtaining images: Create your own [1] Many software programs are available some easy, others more sophisticated and more difficult Capture the screen display or part of the screen by using a specialist program such as Snag It or PaintShopPro Capture the screen display by using short cuts keys (Windows), alt/prntscrn, or Ctrl/PrntScrn 19 Obtaining images: Scanning photographs or drawings agar plate microscopic slides x-rays 35mm slides organic objects (eg a leaf and magnifying glass) inorganic objects 20 Obtaining images: Digital photography Capturing a single frame from a video Digital cameras still and video Digital microscopes x.html 21

8 Manipulating images [1] Captions Rotate Mirror Change colours Tidying up rubbing out, cropping Colouring in Resizing (resample) Changing file format Aspect ratio 22 Limitations and problems Mixing everything (fonts, orientation, format, colour depth) Degradation of images as recompressed or re-edited Steep learning curve to master some tools Various end-user computer configuration 23 How to. Manipulate images using PaintShop Pro Create an image map using FrontPage Create a gif animation using MS Animator 24

9 Remember 1. Use images wisely 2. Use the most appropriate format (file type, size, colour, orientation, compression) 3. Maintain an image s aspect ratio 4. Always keep an original (preferably uncompressed) 25 The last 60 minutes.. What was it about you tell me What didn t you understand? 26 What s next Week 2 Practical: Practical Uses of Internet Services Week 3 Practical: Web Pages Design and Use Week 4 Practical: Using PowerPoint 27

10 Resources PaintShopPro Trial download (55MB) PaintShop Pro Earlier version 3.11 (3MB) is available from MS GIF Animator (1MB) Clip art 28