Get the Best Digital Images Possible What’s it all about anyway? Lorna Olsen Information Technology Services North Dakota State University
Issues to Consider Resolution n Image Size n File Size n Intended Use of the Image n File Formats n
Issues to Consider n Image size u Pixel dimensions of original image (width x height) determine maximum size the image can be without losing quality
Issues to Consider n File Size u The more pixels in an image – the larger the file size u Larger file sizes mean: t longer Web page load times t Longer print times for printed images
Issues to Consider n What’s the intended use of the image? u Print t Print dimensions are more important than pixel dimensions t Higher resolutions produce better quality printed image
Issues to Consider u Online viewing t File size is the most important consideration t Pixel dimensions determine approximate viewing size
Resolution n What IS resolution? u Ability to resolve detail (changes in contrast between pixels) u More commonly used to describe total number of pixels in captured image u The greater the number of pixels captured, the better the resolution – but – u More pixels means larger file sizes
Types of Resolution n Image Resolution u # of pixels per unit of length measured in pixels per inch (ppi) u A high resolution image contains more pixels than an image of the same dimensions with a low resolution
Types of Resolution n Monitor Resolution u # of pixels per unit of length on a monitor measured in pixels per inch (ppi) u Image pixels translate directly into monitor pixels t If image resolution is higher than monitor resolution, image appears larger on screen than it prints
Types of Resolution Common Monitor Resolutions u 640 X 480 u 800 X 600 u 1024 X 768 u 1280 X 1024 n Newer monitors can have even higher resolutions n
Types of Resolution The same image displayed at two different monitor resolutions will appear at different sizes n The monitor’s physical size also influences the size the image appears at n
Types of Resolution n An image displayed on a 19” monitor set to display 1024 X 768 pixels looks much larger than the same image displayed on the same monitor at 1280 X 1024 pixels
Types of Resolution n Output or Printer Resolution u # of ink dots per inch produced by printer measured in dots per inch (dpi) u Higher resolution printers combined with higher resolution images generally produce the best quality
Print Resolution n Appropriate resolution for printing is determined by both the printer’s resolution and the screen frequency (lines per inch – lpi) of the halftone screens used by the printer to produce images
Getting the Right Print Resolution n Computer Graphics Rule of Thumb: u Scan image at 1. 5 to 2 times the screen frequency used by the printer t Screen frequency is usually 133 lpi u 133 lpi x 1. 5 = 200 ppi correct scanning resolution to use
Digital Cameras Camera resolution is measured in terms of the maximum number of pixels the image sensor is capable of capturing n Megapixels – 1 megapixel = 1 million pixels n 3. 1 megapixel camera produces images with 2048 X 1538 pixel dimensions n
Digital Cameras n Assume you need at least a 150 ppi image resolution for good print quality u To get a good 4 X 6 print – you need to capture at least 600 X 900 pixels (150 X 4, 150 X 6) u For 8 X 10 print – you need at least 1200 X 1500 pixels
Digital Cameras Some cameras have multiple resolution settings (pixel dimensions) available n Use lower resolutions for smaller file sizes if you don’t need to enlarge the image for printing n
Image Size n Best to create the image at the final size you want to use u You can always resize images smaller without loss of quality u Resizing the image larger later can degrade image quality
Image Size n Digital Cameras u Start with camera set at highest resolution setting if you’ll need to print a larger image t Use image editing software to resize print dimensions/increase image resolution u If image will be used on Web page, reduce the camera resolution setting to reduce the file size and image dimensions when viewed on screen
Image Size n Scanners u Set scanning resolution as high as necessary t Scan at higher resolutions for both print and online viewing for best quality u Choose the desired print dimensions before scanning t Best to scan larger and rescale smaller, than to scan small and then try and resize larger
Image Size n If you’ve scanned at a higher resolution (200 -300 dpi): u If image is to be used online, use image editing software to lower image resolution to 72 -96 ppi t Image detail captured by higher resolution scan will still be there, but file size will be smaller t Improves quality of images printed from Web pages
File Formats n JPEG (. jpg) Joint Photographic Experts Group u Image is automatically compressed so file size is smaller as camera saves the image as a JPEG file u Most digital cameras use the jpg format by default u Some cameras use a proprietary file format you’ll need to convert to useable formats using image editing software
File Formats u When editing JPEG images, save in another format while editing – each time you resave a JPEG image you lose more data, lowers image quality
File Formats n n Many digital cameras have different quality settings u Hi – usually uncompressed TIFF files u Fine – lowest compression JPEG file, larger file size u Normal – more compression, smaller file size u Basic – most compression, smallest file size Each setting compresses the image with more or less loss of data – affects file size and image quality, not image resolution
File Formats Most scanners allow a choice of different file formats to save the final scanned image n Choose the format that’s best for the intended use of the image n JPEG is best for online images due to image compression – smaller file sizs n TIFF is often best for printing images – no image compression, no loss of data n
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