Grade 8 image file format
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This document discusses different digital image file formats and factors to consider when choosing a format. It explains that graphics file formats can vary in color depth, compression levels, portability, and ability to include transparency. Common formats include TIFF, PNG, GIF, JPEG, and BMP. The best format depends on an image's content and intended use, balancing file size, quality, and compatibility. TIFF offers highest quality but large files, while JPEG is best for photographs on the web due to high compression ratios.
Grade 8 image file format
- 1. DIGITAL IMAGE FORMATS: AN EXPLANATION GRADE 8 - ICT
- 2. GRAPHICS Graphics - anything on the page that is not actual text, from simple line drawings to fully active images found on the World Wide Web. There are many different graphic file formats. The format you choose depends on several factors. 0 10 20 30 40 50 60 70 80 90 1st Qtr 2nd Qtr 3rd Qtr 4th Qtr East West North Chart PhotographButtons
- 3. FACTORS THAT AFFECT GRAPHIC FORMAT • Color depth • Compression • Portability • Transparency
- 4. COLOR DEPTH The number of colors per pixel that can be contained in an image. Most graphics editing programs will allow you to set the color depth for your image. Different graphic formats contain different numbers of colors per pixel. Examples:1-bit Color 2 Colors Per Pixel 8-bit Color 256 Colors Per Pixel 16-bit Color 65.5 Thousand Colors Per Pixel 24-bit Color 16.7 Million Colors Per Pixel
- 5. COMPRESSION Compression refers to how an image is saved in order to reduce the file size. The greater the compression, the lower the quality Two types: Lossless Reduces the file size without losing any pixel data Quality is not compromised Lossy Alters and/or eliminates some data The more the image is reduced, the more the quality is degraded
- 6. After Compression Notice that there is no difference, no data has been lost. LOSSLESS COMPRESSION Before Compression
- 7. Original . . . . . . Final compression LOSSY COMPRESSION Notice that each time the image is saved, the quality is degraded. In the third image, the image is very pixelated.
- 8. PORTABILITY How easily you can open, modify, and view the files on computers using different operating systems, software and browsers.
- 9. TRANSPARENCY Allows the background color of an image to be “eliminated” or made transparent so that the background behind the image can be seen. It makes part of the image invisible, or “see-through.”
- 10. FACTORS TO CONSIDER WHEN CHOOSING A GRAPHIC FILE FORMAT Which file format is best for a particular application? How important is the quality of the image when transferred, copied, or displayed? How important is the speed at which the image transfers or loads? How important is file size?
- 11. NUMBER OF COLORS Images have differing numbers of color within them. Black and white images take up the least amount of space with 1 bit of information. Current video cards are able to display 24 bits of color per pixel. This makes it possible for 16 million colors to be displayed (224 colors). This requires a significant amount of disk space.
- 12. THE FILE TYPES – TIFF (TAG IMAGE FILE FORMAT) TIFF can be lossless or lossy. The details of the image storage algorithm are included as part of the file. TIFF is used almost exclusively as a lossless image storage format that uses no compression at all. Most graphics programs that use TIFF do not use compression. File sizes are quite big.
- 13. THE FILE TYPES – PNG (PORTABLE NETWORK GRAPHICS PNG is a lossless storage format. It looks for patterns in the image that it can use to compress file size. The compression is exactly reversible, so the image is recovered exactly.
- 14. THE FILE TYPES – GIF (GRAPHICS INTERCHANGE FORMAT) GIF creates a table of up to 256 colors from a pool of 16 million. If the image has fewer than 256 colors, GIF can render the image exactly. GIF is "lossless" only for images with 256 colors or less. For a rich, true color image, GIF may "lose" 99.998% of the colors.
- 15. THE FILE TYPES – JPEG (JOINT PHOTOGRAPHIC EXPERTS GROUP) JPG is optimized for photographs and similar continuous tone images that contain many, many colors. It can achieve astounding compression ratios even while maintaining very high image quality. It stores information as 24 bit color. The degree of compression of a JPG is adjustable.
- 16. THE FILE TYPES – BMP (BITMAP) BMP is an uncompressed proprietary format invented by Microsoft. There is really no reason to ever use this format.
- 17. THE FILE TYPES – PSD (PHOTOSHOP DOCUMENT) PSD is a proprietary format used by Photoshop. This is the preferred working format to edit images in the software This package uses layers to build complex images, and layer information may be lost in the nonproprietary formats such as TIFF and JPG. However, it is best to save the product as a TIFF or JPG, so it can be viewed in the future when software changes.
- 18. THE FILE TYPES - SUMMARY TIFF files are generally large. PNG compression can be reversed if needed. GIF results in lose of color information. JPG are the best in terms of compressed files. BMP should be rarely, if ever used. PSD is exclusive to Photoshop.
- 19. TIFF – This is usually the best quality output from a digital camera. JPG – This is the format of choice for nearly all photographs on the web. GIF - For images with fewer than 256 colors and large areas of uniform color like cartoons. Do NOT use GIF for photographic images PNG - For images with large areas of exactly uniform color, but more than 256 colors Also, for display of photographs exactly without loss of quality on the web. WHEN SHOULD YOU CHOOSE EACH?
Editor's Notes
- #5: Teachers: Color Depth here refers to the number of colors that can be contained in the image. It is not referring to the number of colors which can be displayed on a computer monitor. Just for Fun (supplemental, not required): If you would like to integrate math into your curriculum, you could have students calculate the number of colors which can be displayed in an image based on the bits of color. To calculate this, raise 2 to the power of the color resolution. (Because each bit can contain 2 pieces of data: 1 or 0). So 8-bit color = 2^8 = 256 color possibilities per pixel. 1-bit color = 21 = 2 colors 8-bit color = 28 – 256 colors 16-bit color – 216 = 65.5 thousand colors
- #6: Teacher Note: Lossy compression deletes some of the data that it deems unnecessary since the human eye is not very sensitive to changes in color over small distances.
- #7: Teacher Note: Lossless compression looks for recurring patterns and replaces each occurrence with an abbreviation. If there isn’t a lot of redundant information, then the file size may not be decreased very much. Lossless compression is used when it is important for the compressed image to look exactly like the original image.
- #8: Teacher Note: In lossy compression, the more times you save the image, the more data that is eliminated and the more the quality of the image is degraded. So every time you save a JPG file, the quality is degraded more. To prevent this, make all of the editing changes in the editing software program’s native format or in a bitmap format before saving the final image as a JPG or other compressed format which uses lossy compression.
- #10: Teacher Note: To illustrate this concept, hold up a photograph on a piece of paper and hold a piece of colored paper behind it. You cannot see the color through the image. Next, hold up a transparency with a piece of colored paper behind it. The background color does change.
- #11: Teacher Note: The answers to these questions will help determine which graphic file type should be used.