Dallas Genealogical Society Technology Special Interest Group Thursday, April 2, 2015

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1 Dallas Genealogical Society Technology Special Interest Group Thursday, April 2, 2015 Tony Hanson Webmaster Technology Special Interest Group Leader Director - Education

2 Demystifying Digital Images Tony Hanson Webmaster Technology Special Interest Group Leader

3 What we will be talking about What is a Digital Image How Digital Images are Created Numeric Representation of Colors Histograms How Digital Cameras and Scanners Work Digital File Formats Image Resolution and Size Printing Images Metadata Resizing Images 02/2015 3

4 What is a Digital Image? A numeric representation of an image Comprised of an organized collection of Pixels (Picture Elements) Rows & Columns Pixel a.k.a. Dot When viewed on a suitable display (or printed) it appears to be an exact copy of the original image 02/2015 4

5 Mosaic Image Prairie Passage by Carl and Sandra Bryant Eagleville, MO Welcome Center 02/2015 5

6 02/2015 6

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8 Notre Dame Cathedral, Montreal Canada

9 How Are Digital Images Created? Born Digital Created using software that directly creates the digital file File -> Save As -> 02/2015 9

10 This is an image file created directly from Publisher 02/

11 Graphic Images Has relatively Few colors Usually a (relatively) small file Some file formats are customized to support this type of image 02/

12 How Are Digital Images Created? Converted to a digital format Scanner Digital Camera These both use a Charge Coupled Device (CCD) to convert the optical image into an appropriate numeric representation 02/

13 CCD: Converts Light to a Numeric Value x Light y z CCD Memory Color values are represented by three components: Red Green Blue 02/

14 Color Palette 02/

15 Red Memory 02/ CCD

16 Green Memory 02/ CCD

17 Blue Memory 02/ CCD

18 White Memory 02/ CCD

19 Black Memory 02/ CCD

20 Purple Memory 02/ CCD

21 Gray Note that the color values are all the same for Gray Memory 02/ CCD

22 Numeric Representation Color Gray Scale Black and White 02/

23 Numeric Representation: Color 24 Bit Color Depth Each component value (Red, Blue and Green) can range from 0 to 255 In Binary, the range is 0: : Colors x 8 bits each = 24 bits 02/

24 255 in Binary Notation = /

25 48 Bit Color 48 Bit Color Depth Each component value (Red, Blue and Green) can range from 0 to 65,535 In Binary, the range is 0: : Colors x 16 bits each = 48 bits Provides more colors More steps between Black and White 02/

26 65,536 in Binary Notation = = = /

27 Black is Still Black Memory 02/ CCD

28 White is still White Memory 02/ CCD

29 More shades of Blue (and Red, Green ) Memory 02/ CCD

30 Gray Scale Ranges from White through various shades of Gray to Black Has equal Red, Green and Blue values Since each of the three values is the same it is only necessary to record it once This limits the colors available, but may produce a high quality image that requires less storage 02/

31 Grayscale Palette 02/

32 Gray Scale Color Depth Usually available in 8 bit and 16 bit color depth The end points in both cases are still White and Black 16 bits gives you more granularity More shades of Gray 02/

33 Black and White ( a.k.a. Line Art ) Each Pixel can have one of two values: 0 => White 1 => Black It is usually possible for you to modify the threshold between what is considered Black and what is considered White These values (0 or 1) can be stored in a single bit, significantly reducing storage requirements 02/

34 Size Matters! Source: A few scanning tips 02/

35 How many Pixels at each color? How Many Pixels , 0, 255 0, 255, 0 255, 0, 0 0, 0, 0 255, 255, 255 Black Blue Green Red White

36 A Histogram! How Many Pixels 0, 0, 255 0, 255, 0 255, 0, 0 0, 0, 0 255, 255, 255 Black Count of How Many Pixels at each color White s

37 Histogram Shows a count of each color in the image Helps understand how much contrast the image has Probably most useful to photographers (useful for judging exposure) Also useful when adjusting scanner threshold settings s

38 Digitation Tools Camera Scanner 02/

39 Digital Camera Light Aperture Shutter Charge Coupled Device Lens Image s

40 Image on a Charge Coupled Device (CCD) Pixels

41 CCD Characteristics How sensitive it is to Light Its Size How many Megapixels Aspect Ratio Ratio of Width to Height (Pixels) A square would have an aspect ratio of 1 Typical values for a camera are 1.3 or 1.5 (rectangular) 02/

42 iphone 6 Records images in a 3264 by 2448 format 3264 x 2448 = 7,990,272 Pixels (8 MegaPixels) 3264 / 2448 = 1.33 to 1 Aspect Ratio

43 Scanners Unlike a camera, a scanner has only a single row of CCD sensors The sensor is moved across the document to be scanned and takes many samples in the process 02/

44 Flatbed Scanner Light Document Glass Charge Coupled Device Mirrors

45 Document

46 My Simple Document Tony. 02/

47 Each Line scanned as a series of Pixels oooooooooo oooooooooo oo oo oo oo oooooooooo oooooooooo ooo oo oo oo oo oo oo oo oo oo oooo oo oo oo oo oo oo oo oo oo oo oo oooo oo oo oooooooooo oo ooo oo oo oooooooooo oo oo oo o

48 Scanner Specifications Optical Resolution The Pixels per Inch capability of the CCD (Horizontal resolution) Hardware Resolution The resolution of the mechanism that moves the CCD across the document (Vertical Resolution) Interpolated Resolution Using software to increase resolution by predicting what might be in between two scanned pixels 02/

49 How are digital images saved? 02/

50 Digital File Formats A digital file format defines the way that the digital information will written into (and read from) the file Many file formats have been created over the years to address different needs and concerns Wikipedia has identified 262 different graphics file formats! 02/

51 Image File Format Characteristics Raster vs. Vector Compression Type Color Depth Color Indexing Transparency Metadata Interlacing Animation Layers Color Management 02/

52 Raster vs. Vector Vector formats deal with lines and shapes These scale (adjust to different sizes and display formats) very well Useful in graphic and scientific applications Raster formations deal with pixels/dots The focus of our discussion 02/

53 Compression Not all formats perform compression Those that do fall into two classes: Lossless No loss of resolution or color information Results in larger files Lossy Some irreversible loss of resolution or color information in the compression process Results in smaller files 02/

54 Color Depth Defines the number of bits available to encode color Usually can be modified Ranges from 1 to 48 bits 02/

55 Color Indexing Some formats limit the number of discrete colors that can be utilized They provide a fixed size matrix where the colors utilized in the image can be specified During the encryption, each pixel s color is referenced to this table Advantage: Smaller File Disadvantage: Limits the color granularity of the image 02/

56 Transparency Not supported by all formats Allows the background to be viewed behind the image Achieved by designating a specific color in the image When displayed, image pixels with the designated color are discarded and replaced the appropriate pixel from the background image 02/

57 Metadata Not supported by all formats Descriptive information about the image Appended to the image file There are a variety of metadata types/standards that can be used The most common are: Exif Photographic Information IPTC Descriptive Information XMP ISO Standard 02/

58 Popular Image File Formats 02/

59 TIFF Compression: None Color Depth: 1,2,4,8,16,24,32 bit Color Indexing: Yes Transparency: Yes Metadata: Yes Comments Can be compressed with external/3 rd party compression tools 02/

60 JPEG Compression: Lossy Color Depth: 12/24 bit Color Indexing: No Transparency: No Metadata: Yes Comments Amount of compression can be varied Repeated saving compounds color loss a.k.a. JPEG Artifacts Good for photos, bad for text or graphics 02/

61 JPEG vs TIFF Original TIFF File 5036 x 8326 Pixels 600 dpi 25,667 KB Large JPEG 5036 x 8326 Pixels 600 dpi 15,360 KB Medium JPEG 5036 x 8326 Pixels 600 dpi 3,146 KB Small JPEG 5036 x 8326 Pixels 600 dpi 1,567 KB 02/

62 JPEG Artifacts Loss of: True Color Correct Intensity Resolution 02/

63 GIF Compression: LZW Color Depth: 1,2,3,4,5,6,7,8 bit Color Indexing: Yes Transparency: Yes Metadata: Yes Comments LZW compression had licensing/legal issues that limited its widespread use 02/

64 PNG Compression: Lossless Color Depth: 1,2,4,8,16,24,32 bit Color Indexing: Yes Transparency: Yes Metadata: Yes Comments Much better choice than JPEG Some consider it to be nearly as good as TIFF W 3 endorsed replacement for GIF 02/

65 JPEG 2000 Compression: Lossy or Lossless Color Depth: Color up to 48 bit Color Indexing: No Transparency: Yes Metadata: Yes Comments Popular with governments and institutions Not yet widely supported in the consumer market Eventual replacement for TIFF 02/

66 Metadata Data about something Digital Metadata is Embedded in each file Pre-Digital Metadata Date (Aug 61) Description (Hanson Evans Tollief s Fam)

67 File Format Image Data (Pixels) Format Specific (TIFF, JPG, PNG, etc ) Camera Data (EXIF) Exchangeable Image File Format MetaData

68 IPTC: International Press Telecommunications Council The most widely recognized standard for Metadata Established in 1965 by a group of news organizations

69 IPTC Defined For Many Image File Types You can define IPTC metadata for the following image formats:.tif.jpg.png But NOT for these image formats:.bmp.gif

70 Viewing or Printing an Image Requires software that understands the file format Extracts the data and re-creates the image Computer monitors and printers present images in very different ways This may impact how the image appears to you 02/

71 How Big Is That Image? Digital images have no size However, they do have characteristics that may limit how large you want it to be when it is displayed or printed 02/

72 This is a stamp The original is 1 ¼ inched tall and 1 inch wide Scanned at 300 dpi 300 x 375 dpi s

73 1920 x 1080 Resolution A 1 ¼ inch tall stamp scanned at 300 dots per inch

74 1280 x 720 Resolution A 1 ¼ inch tall stamp scanned at 300 dots per inch

75 800 x 600 Resolution A 1 ¼ inch tall stamp scanned at 300 dots per inch

76 Pixels and Colors Computer Monitors will always display images with truer colors when compared to most home printers This is because each pixel on a monitor can display the entire possible range of colors A printer can only approximate the color using a mixture of colors 02/

77 Printing Images Printers used at home (generally) can only print dots Black and White printers can only create black dots (or no dots at all a.k.a. white ) Two modes of printing: Line Art Shades of Gray 02/

78 Line Art Dot for dot representation of the image Good for text & some (limited) types of images 02/

79 Shades of Gray 02/2015 HP 1320 Laser Printer: Prints at 1200 dpi 79

80 Shades of Gray 02/ Scanned at 9600 dpi

81 Grid Sizes 6 x 6 37 Shades of Gray, reduces resolution by a factor of dpi -> 100 Line Per Inch (lpi) 1200 dpi -> 200 lpi 7 x 7 50 Shades of Gray, reduces resolution by a factor of 7 8 x 8 65 Shades of Gray, reduces resolution by a factor of 8 10 x Shades of Gray, reduces resolution by a factor of 10 02/

82 Printing Color Images Printers used at home (generally) can only print dots Color printers can only print the colors for which they have ink Cyan, Magenta, Yellow and Black Cyan, Magenta, Yellow, Black, light Cyan, Light Magenta 02/

83 Printing Colors Colors are created by placing different colors close together One color image (pixel) requires many printer ink dots The human eye cannot distinguish the individual colors and will perceive the mixed color Called Dithering This is why (for example) we need a 1200 dpi printer (ink dots) to print an image at 250 dpi (pixels). 02/

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86 Printer dpi Specifications Printer specifications are real, accurate and meaningful, but are not to be confused with image resolution Printer ink dots and image pixels are very different things 02/

87 Rule of Thumb The effective resolution (image pixels per inch) should be in the range of dpi (for the actual printed dimensions) Sending images at higher resolutions is counter productive Files are larger Most of the pixels will be thrown away May actually decrease the quality of the printed image 02/

88 1 ¼ x 1 inch Original Scanned at 300 dpi OK to print it at its original size Effective resolution would be 300 dpi Could print it twice as large (2 ½ x 2 inches) Effective resolution would be 150 dpi Larger images would probably not look good If desired, scan again at higher dpi setting 02/

89 Image Resizing Scaling Cropping Resizing 02/

90 Image Resizing: Scaling Scaling Specifying a dpi value to use when printing Just a numeric value that is saved with the image and used if/when it is printed The original image remains unchanged Defined for TIF and JPG Not all applications pay attention to this value 02/

91 Scaling Stretching or shrinking the image to fit a specified area Can be done while scanning or afterwards.. 02/

92 Scaling: Photoshop 12 Image -> Resize -> Image Size 02/

93 Image Resizing: Cropping Selected part of the original image The original image remains unchanged 02/

94 Image Resizing: Resizing Resizing Alters the dpi of the image The original image IS CHANGED Best to work on a copy! Works better when you DECREASE the dpi value You can increase, but you are asking the software to make an educated guess about the pixels it adds 02/

95 Resizing: Photoshop 12 Image -> Resize -> Image Size 02/

96 Other Modifications Orientation (Portrait / Landscape) Contrast Modifying what is considered white and what is black Color Balance File format conversions Much more Ask Sandra Crowley to give her Image Editing seminar again. 02/

97 More on Size and Resolution Let s assume we want to digitize a document that is 8.5 x 11 inches (the entire document) Using an 8 Megapixel Digital Camera Using a Flatbed Scanner Questions: What is the best resolution I can obtain using the camera? What dpi setting would I need to use on the scanner to obtain better resolution? 02/

98 Best Case We want to maximize the resolution of the image by using as many pixels as possible Use all of the horizontal pixels (2448) Determine how many vertical pixels we can use /

99 Math! 2448 / 8.5 = x / 11 x = ( 11 * 2448) / 8.5 x = Pixels 11 inches Unused Pixels: 2448 Pixels 8.5 Inches ( ) * 2048 = 96 * 2048 = 196,608 (2.5%) 02/

100 What is our effective resolution? 2448 Pixels / 8.5 inches = 288 Pixels/inch 3168 Pixels / 11 inches = 288 Pixels/inch To obtain a higher resolution image using a scanner we could scan it at 300 dpi. 02/

101 Another Example I have a slide (1 inch High x 1.5 inches Wide) I want to print a 4 x 6 image What dpi setting do I need to use on the scanner to scan the slide? 02/

102 Solution I want to sent a 4 x 6 image at a density of 300 dpi to the printer. A 4 x 6 image is exactly 4 times the size of the slide (they have the same Aspect Ratio) 1 x 4 = x 4 = 6 Since I am enlarging the image by a power of 4, I will also be decreasing the resolution by a power of dpi (printed) = dpi (scanned) / 4 dpi(scanned) = 4 * 300 = 1200 dpi 02/

103 1 inch 1200 Pixels 6 inches 1800 Pixels (300 dpi) 1.5 inches 1800 Pixels 4 inches 1200 Pixels (300 dpi) 02/

104 What if I wanted an 8 x 10? (6 * 1 x 1.5) = 6 x 10 Not big enough! (8 * 1 x 1.5) = 8 x 12 Too big! Need to crop 2 inches off the width Could take 1 inch off each side Let s assume that this will work for the image 02/

105 Solution We still want an effective density of 300 dpi Enlarging it by a factor of 8 8 * 300 = 2400 dpi Scan the slide at 2400 dpi, crop to 8 x 10 and print! Check: ( 1 * 2400 ) / 8 = 300 dpi ( 1.5 * 2400) / 12 = 3600 / 12 = 300 dpi 02/

106 References/Resources A few scanning tips Wayne Fulton Invaluable reference! Also good tips on photography 02/

107 Scanning 101 The Basics * START - The First Fundamental Concept Video Resolution - How much to scan? Say No to 72 dpi - It's a false notion Images for television or for PowerPoint Printing Resolution - Scaling and Resampling Finding the Scaling and Resampling Menus Printer Resolution - How much to scan? Line art and Threshold - Copy and OCR, Printed Text Line art and Grayscale Scanning for Fax Descreen to remove Moiré Interference Images in magazines/books/newspapers Interpolated Resolution dpi? Photo Resolution - How much can we scan? Image File Formats - Which format? Video Boards Transparent Media Adapter - 35 mm slides? What about Film Scanners? Dynamic Range - 24 bit or 36 bits? 02/

108 Wikipedia Comparison of graphics file formats 02/

109 Epson Technical Brief Discusses Image Quality, Performance and Flexibility of Epson Scanners A good overview of technical aspects of scanner design and operation 02/

110 Questions? 02/

111 Thank You! Tony Hanson Webmaster Technology Special Interest Group Leader 02/

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