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Working With Images April 21, 2005 Why this workshop? To end the frustrating hours spent trying to print posters. To maximize the quality of your posters, manuscripts, PowerPoint presentations and web images. To inject some good information into the informal support network. Agenda

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working with images

Working With Images

April 21, 2005

why this workshop
Why this workshop?
  • To end the frustrating hours spent trying to print posters.
  • To maximize the quality of your posters, manuscripts, PowerPoint presentations and web images.
  • To inject some good information into the informal support network.
  • Image basics
  • Resolution
  • Color management
  • File formats
  • Printing
  • Incorporating images into documents
step 1 forget everything you know about working with graphics

Step 1: Forget everything you know about working with graphics!

… unless I ask a question

graphic types
Graphic Types
  • Two fundamental types of graphics
    • Vector graphics
    • Raster graphics (a.k.a. bitmaps)
vector vs raster
Vector vs. Raster


Draw a 1024 x 768 pixel rectangle and fill it with light yellow. Draw a 885 x 628 rectangle with no fill and a 6pt black stroke. This makes a 504K Illustrator file.


Make a 1024 x 768 pixel bitmap with a bunch of light yellow pixels and a few black pixels. This makes a 2.25MB image.

graphic types8
Graphic Types
  • Two fundamental types of graphics
    • Vector graphics
    • Raster graphics (a.k.a. bitmaps)
  • Graphics software used to do one type or the other. That is no longer true.
  • You need to pay attention to which type of graphic is being used and the conversion from vector to raster.
vector graphics
Vector Graphics
  • Consist of directions for drawing objects
  • File size depends on number and complexity of objects.
  • Do not have a “resolution” so they can be scaled without affecting image quality
  • Traditionally produced by drawing applications like Illustrator or Canvas
vector graphics10
Vector Graphics
  • Best used for images consisting of geometric shapes and lines (i.e. maps, charts, stratigraphic sections, etc.)
  • Text is generally a vector graphic.
  • It’s hard to get into too much trouble with vector graphics except when you convert from vector to raster.
  • Beware of overly complex digitized maps.
  • Beware of ArcGIS exports!
raster graphics
Raster Graphics
  • Image mapped out by grid (raster) of pixels.
raster graphics bit depth
Raster GraphicsBit Depth
  • Each pixel is represented by 1 to 64 bits depending on color mode.

Bitmap Grayscale RGB CMYK

1 bit

21 = 2 values

0 = black

1 = white

8 bits

28 = 256 values

0 = Black

255= white

This gray is 119

24 bits

224 = 16,777,216

8 bits for each channel (R,G & B)

This is 255, 153, 0

32 bits

232 = 4,294,967,296

8 bits for each channel (C,M,Y & K)

This is 0,44,95,0

image color modes
Image (Color) Modes
  • PhotoShop (and other applications) can work in numerous image modes.
  • Grayscale, Indexed, RGB and CMYK are the most common.
  • Use grayscale for “black and white” images.
  • Use indexed mode when creating GIFs.
  • Use RGB for all other images.
raster graphics image size
Raster GraphicsImage size
  • Image size (bits) = pixel dimension X bit depth
  • Divide by 8192 to get Kilobytes
  • Increasing the number of pixels geometrically increases the image size.
  • 500 x 500 24 bit image ~ 732K
  • 1000 x 1000 24 bit image ~ 2.9MB
  • 2000 x 2000 24 bit image ~11.4MB
raster graphics image scaling

100 x 1008/9s of original pixels discarded

300 x 300Original

Raster GraphicsImage scaling
  • Raster graphics are not scalable. Changing image size requires adding or removing pixels.

600 x 6003 new pixels created for each original pixel

raster graphics file size
Raster GraphicsFile size
  • File size does not usually equal image size.
  • Many file formats, such as JPEG and GIF, employ compression that shrinks the file size below the image size.
  • Example: a 1024 X 768 red box is 2.25MB, but saved as medium quality JPEG the file shrinks to 4.8KB; GIF is 1.5KB.
critical take home point 1
Critical take-home point #1
  • No matter what size you shrink the file to, the image size stays the same!

Critical take-home point #2

  • It’s the image size that matters when printing or displaying images! Compressed files such as a JPEGs are uncompressed to the full image size before they are used.
what is resolution
What is resolution?
  • It depends on whether you are talking about an image’s specification, a printer’s print quality, a scanner’s hardware, a monitor’s pixel dimension or a digital camera’s CCD.
  • Resolution is one of the most misunderstood and misused terms in graphics.
why is resolution important
Why is resolution important?
  • Properly specified image resolution is critical to print quality, printing speed and printer stability.
  • Improperly specified resolution can lead to all sorts of trouble (i.e. waiting 2 hours while the printer decides not to print your document).
device resolution
Device Resolution
  • For printers it specifies the number of ink spots that can be printed per unit area
  • For scanners it specifies the physical spacing of optical sensors
  • For monitors it specifies the total number of displayed pixels
  • For digital cameras it specifies the total number of light-receptive cells in its sensor
image resolution
Image Resolution
  • Image size has no physical reality; it just specifies the total number of pixels which have no inherent size.
  • When an image is displayed or printed it takes on a physical size.
  • Image resolution controls the conversion between the image size and the physical display size.
the acronym game
The Acronym Game
  • DPI: Dots Per Inch
  • PPI: Pixels Per Inch
  • SPI: Samples Per Inch
  • LPI: Lines Per Inch (a.k.a. screen frequency)
display monitor resolution
Display/Monitor Resolution
  • The dpi resolution specified in image files has no impact when they are displayed on computer monitors or data projectors.
  • Monitors can only display at their set resolution.
  • Each pixel in the image file is mapped to a pixel on the monitor.
which image is 20dpi and which is 600dpi
Which image is 20dpi and which is 600dpi?

It does not matter because they are both 500 x 350 pixels!

600dpi 20dpi

proper image dimensions for display
Proper Image Dimensions for Display
  • Figure out the size of your display device. 1024 x 768 is most common these days.
  • Size your images relative to display size
    • 1024 x 768 = full screen
    • 874 x 618 = image with ~1 inch border
    • 512 x 384 = 1/4 screen
  • Consistent image size adds a look of professionalism. Develop a set of preferred sizes and stick with them.
what about 72 96 dpi
What about 72/96 dpi?
  • In the old days the common monitor at native resolution had an effective resolution of 72dpi. Today it varies.
  • Example: The display width of my 17-inch CRT monitor is 12.25”. In 1024 x 768 mode this gives an effective resolution of ~84dpi.
  • Forget about 72/96dpi—it’s meaningless when displaying images.
scanner resolution samples per inch spi
Scanner ResolutionSamples Per Inch (spi)
  • The native resolution of a scanner is determined by the spacing of sensors in its scanning bar.
    • UMAX 1100 in Image lab = 1200spi
    • Epson Perfection 2400 Photo in Mac lab = 2400spi
    • Minolta Dimage slide scanner = 2400spi
  • Scanning at the native resolution gathers the maximum amount of info from the original document.
scanner resolution samples per inch spi29
Scanner ResolutionSamples Per Inch (spi)
  • Always scan at the native resolution and then let PhotoShop downsize the image if needed.
    • Exception: If you are in a hurry and you know your image is destined for low resolution use like the web or PowerPoint presentations, then scan at lower resolution for increased scanning speed.
  • Never scan at a setting higher than the native resolution. This causes the scanner software to make up pixel data. Let PhotoShop do the upsizing.
printer basics
Printer Basics
  • Images are printed as a series of dots. Your brain interprets the dots as continuous tones.
  • The dots are solid colors (black, cyan, magenta or yellow).
  • The resulting color on the page is a function of dot concentration and the ratio between the different colored dots.
  • The conversion of your image into the series of dots is halftoning.
example of halftones
Example of Halftones

Enlargement illustrates what halftone would look like if this image was printed on the color laser writer or plotter.

printer resolution dots per inch dpi
Printer ResolutionDots Per Inch (dpi)
  • Only applies when printing a monochrome (one color) image.
    • Text or 1-color line art (black, cyan, magenta or yellow).
  • Completely irrelevant when printing all other images.
  • I repeat, completely irrelevant when printing all other images!
printer resolution lines per inch lpi
Printer ResolutionLines Per Inch (lpi)
  • Also known as line screen or screen frequency
  • Specifies the number of halftone cells (spots) printed per inch
  • The LPI is much lower than the DPI and is generally hard to determine because printer manufacturers do not advertise it.
printer resolution the importance of lpi
Printer ResolutionThe importance of LPI
  • Image quality peaks when the resolution is set to ~2 times the line screen.
  • Many images look just fine at 1.2 - 1.5 times the line screen.
  • Sending images at resolutions higher than 2.5 times the line screen degrades image quality and clogs the printer with needlessly large files.
proper image resolution for printing
Proper Image Resolution for Printing
  • Use 100- 140dpi for normal images lacking fine detail or where the fine details are not critical.
  • Bump up to 140-200dpi when the fine details count or you are printing small images.
  • Go up to 200-255dpi when printing small detailed images.
  • Never use a resolution >255dpi.
  • Experiment with resolutions <100dpi on low-detail images such as backgrounds.
impact of proper image resolution
Impact of Proper Image Resolution
  • Let’s take the example of a color image we want printed at 10 x 8 inches
  • At 140dpi the image is 4.5MB
  • At 200dpi the image is 9.4MB
  • At 600dpi the image is 84.4MB
  • The 600dpi file is 19x larger than 140 dpi and 9x larger than the 200dpi file.
impact of proper image resolution the extreme case
Impact of Proper Image ResolutionThe Extreme Case
  • Let’s take the extreme example of a color image 12” tall spanning a 5’ poster
  • At 120dpi the image is 30.4MB
  • At 160dpi the image is 54MB
  • At 600dpi the image is 759.4MB
  • 120dpi is fine for almost any image you’ll print at this size. 160dpi is plenty for even finely detailed images. 600dpi makes the plotter go BOOM!
critical take home point 3
Critical take-home point #3
  • Less is more when setting image resolution. Never use an image resolution higher than than you need!
sizing images in photoshop
Sizing Images in PhotoShop

Use these boxes when sizing for display

Use these boxes when sizing for printing

Turn Resample Image off when you want to change resolution without changing image size

Use Bicubic Smoother when upsampling and use Bicubic Sharper when downsampling

color management

Color Management

There be monsters here…

what color is this
What color is this?


Nope. It’s 100110000001001111111111

the monsters of color
The Monsters of Color
  • Computers cannot see color. To them images are only a collection of 1s and 0s.
  • Monitors cannot see color. To them images are just electrical signals that tell them how to adjust electron flow.
  • Printers cannot see color. To them images are only a set of directions on how to control printheads.
the rgb vs cmyk complication
Red, Green, Blue

Used by monitors and data projectors

Works by adding colors together (additive)

Red+Green+Blue = White

Cyan, Magenta, Yellow, Black

Used by printers

Works by absorbing color (subtractive)

Cyan+Magenta+Yellow =Black

Imperfections in ink absorption causes C+M+Y= muddy brown

Black (K) is added to fix the problem

The RGB vs. CMYK Complication
the reality of color
The Reality of Color
  • Image color is device-dependent. It varies depending on the physical characteristics and configuration settings of the computer, monitor and printer.
    • Example: In a store the TVs are often all tuned to the same program. They are all receiving the same input signal yet they all display slightly different colors.
color management47
Color Management
  • Color management is the science of displaying and printing images with consistent color across different computers and printers.
  • It’s as mysterious as theoretical physics, but fortunately we can get by without knowing too many of the details.
color spaces
Color Spaces
  • Color spaces are 3D models used to represent a range of real-world colors using numbers.
  • Each color space contains a different sub-set of real-world colors (check out the Color Sync utility).
  • Color profiles define the color space and are the basis for all color management operations.
working space vs device spaces
Working Space vs. Device Spaces
  • The Working Space Profile defines the color space within the application.
    • You must specify the working space.
    • In Illustrator, PhotoShop, and InDesign each image has its own working space profile.
  • Device Space Profiles define the color behavior of the device (monitor, printer, scanner, digital camera, etc.).
    • For most devices you just select the proper manufacturer’s profile.
    • However, you should create your own monitor profile.
working space
Working Space
  • Keep images in RGB mode
  • Specify the sRGB color space (sRGB IEC 61966-2.1)
  • This color space closely matches the color range displayed by monitors.
  • The color laser printer and both HP plotters are configured to color match images created in the sRGB color space.
setting working space profile
Setting Working Space Profile
  • Open the color settings dialog box

Set RGB working space to sRGB

Set RGB color management policy to “convert to working space”

Turn on “Ask when opening” and “Ask when pasting”

Illustrator color setting dialog box. Other applications have similar dialog boxes.

monitor profile
Monitor Profile
  • To display color accurately, applications must know how your monitor behaves.
    • what color is white
    • how it displays color tones
    • what actual color it produces when fed pure red, green or blue signals.
  • The monitor profile tells applications how your monitor behaves.
  • Most factory CRT monitor profiles do not accurately represent the monitor's behavior .
critical take home point 4
Critical take-home point #4
  • You must pay attention to your monitor profile if you want accurate colors!
monitor calibration
Monitor Calibration
  • Both Mac and Windows users have the ability to create custom profiles for their monitors.
  • The utility is built into the Mac “Displays” system preference dialog box.
  • On Windows you need Adobe Gamma which is a control panel installed along with Photoshop.
monitor calibration how to
Monitor CalibrationHow to
  • Set a familiar desktop picture you can use to assess color quality.
  • Mac: Open the Displays control panel, select the color dialog box and click on “calibrate”.
  • Windows: Open the Adobe Gamma control panel
  • Follow the utilities directions.
file formats

File Formats

This used to be simple…

file formats new complications
File FormatsNew Complications
  • Traditionally raster-only formats like TIFF now support vector graphics and other image features like layers.
  • Traditionally closed formats like PDF are now editable.
  • Applications handle the new format features differently.
  • The best I can do is give some general guidelines.
loss less vs lossy compression
Loss-Less vs. Lossy Compression
  • Loss-Less: Files are compressed without altering the pixels. Repeated saves do not degrade the image. Examples: RLE, LZW and ZIP
  • Lossy: The act of compressing the file permanently alters the pixels. Each iteration of saving does more damage. Example: JPEG
  • Rule of thumb: Don’t use lossy compression on working images nor on images destined for printing.
formats for working images
Formats for Working Images
  • The retention of editing flexibility is paramount.
  • Native application formats (i.e. PhotoShop or Illustrator) are best.
  • TIFFs are a good choice if you have to move images across many applications.
formats for archiving images
Formats for Archiving Images
  • You want a format that preserves as much editing flexibility as possible.
  • You want a format that will be readable in the future by many applications.
  • TIFF is the hands-down favorite.
  • PDF and EPS files are also good.
  • Native application formats are the most flexible, but have long-term compatibility concerns.
formats for the web
Formats for the Web
  • File must compress well to minimize network bandwidth requirements.
  • File format must be readable by web browsers.
  • JPEG, GIF and PNG are the industry standards. PDF is also common.
  • Use care when compressing JPEGs.
  • PNG supports both raster and vector data.
formats for printing
Formats for Printing
  • The format must support color matching.
  • The format must be easily digestible by printers and page layout applications.
  • TIFF, EPS, PDF and PostScript are the industry standards.
  • Native application formats also work well.
  • Watch out for compression and downsampling of raster data.
the printing process
The Printing Process
  • Printers only print raster images.
  • When you print complex files like posters, the computer sends the printer a Postscript file that contains both raster and vector data.
  • The printer then converts (RIPs) the file into one giant raster image.
  • The amount of memory needed for the RIP depends on the file size and complexity.
embedded files
Embedded Files
  • Embedding files incorporates the image data into the document file
  • Creates a single file for the entire document
  • Quickly leads to very large files
  • Slow to load, save and display
  • Cumbersome to edit
linked files
Linked Files
  • Linking a file incorporates a small version of the image into the document as a place holder.
  • When printing or displaying, the computer links back to the original file.
  • Images are edited in their native application and the changes are automatically incorporated in the document.
linked files69
Linked Files
  • Documents with linked files are relatively small so they open fast and do not bog down the computer.
  • Caution: Changing the relative location of the document and link files breaks the link.
  • Linked files can often be embedded later if you need the entire document in one file.
images in powerpoint
Images in PowerPoint
  • File links in PowerPoint are very fragile.
  • Embed all files in PowerPoint.
  • If you need to use linked files, like video clips, save your PowerPoint presentation as a PowerPoint Package.
  • Use JPEG, GIF or PNG format.
  • Scale images to the proper pixel resolution at 104dpi to simplify importing.
images in illustrator and indesign
Images in Illustrator and InDesign
  • Use linked images to improve workflow and versatility.
  • Use native format for PhotoShop files, TIFF for rasters from other programs.
  • Scale images as needed in document, but then rescale originals.
  • Embed linked images to make portable file.