Information Technology Services North Dakota State University Lorna Olsen Get the Best Digital Images Possible What’s it all about anyway?

Issues to Consider Resolution Resolution Image Size Image Size File Size File Size Intended Use of the Image Intended Use of the Image File Formats File Formats

Issues to Consider Image size Image size  Pixel dimensions of original image (width x height) determine maximum size the image can be without losing quality

File Size File Size  The more pixels in an image – the larger the file size  Larger file sizes mean:  longer Web page load times  Longer print times for printed images Issues to Consider

What’s the intended use of the image? What’s the intended use of the image?  Print  Print dimensions are more important than pixel dimensions  Higher resolutions produce better quality printed image Issues to Consider

 Online viewing  File size is the most important consideration  Pixel dimensions determine approximate viewing size Issues to Consider

Resolution What IS resolution? What IS resolution?  Ability to resolve detail (changes in contrast between pixels)  More commonly used to describe total number of pixels in captured image  The greater the number of pixels captured, the better the resolution – but –  More pixels means larger file sizes

Types of Resolution Image Resolution Image Resolution  # of pixels per unit of length measured in pixels per inch (ppi)  A high resolution image contains more pixels than an image of the same dimensions with a low resolution

Monitor Resolution Monitor Resolution  # of pixels per unit of length on a monitor measured in pixels per inch (ppi)  Image pixels translate directly into monitor pixels  If image resolution is higher than monitor resolution, image appears larger on screen than it prints Types of Resolution

Common Monitor Resolutions Common Monitor Resolutions  640 X 480  800 X 600  1024 X 768  1280 X 1024 Newer monitors can have even higher resolutions Newer monitors can have even higher resolutions Types of Resolution

The same image displayed at two different monitor resolutions will appear at different sizes The same image displayed at two different monitor resolutions will appear at different sizes The monitor’s physical size also influences the size the image appears at The monitor’s physical size also influences the size the image appears at Types of Resolution

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 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

Output or Printer Resolution Output or Printer Resolution  # of ink dots per inch produced by printer measured in dots per inch (dpi)  Higher resolution printers combined with higher resolution images generally produce the best quality Types of Resolution

Print Resolution 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 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

Computer Graphics Rule of Thumb: Computer Graphics Rule of Thumb:  Scan image at 1.5 to 2 times the screen frequency used by the printer  Screen frequency is usually 133 lpi  133 lpi x 1.5 = 200 ppi correct scanning resolution to use Getting the Right Print Resolution

Digital Cameras Camera resolution is measured in terms of the maximum number of pixels the image sensor is capable of capturing Camera resolution is measured in terms of the maximum number of pixels the image sensor is capable of capturing Megapixels – 1 megapixel = 1 million pixels Megapixels – 1 megapixel = 1 million pixels 3.1 megapixel camera produces images with 2048 X 1538 pixel dimensions 3.1 megapixel camera produces images with 2048 X 1538 pixel dimensions

Assume you need at least a 150 ppi image resolution for good print quality Assume you need at least a 150 ppi image resolution for good print quality  To get a good 4 X 6 print – you need to capture at least 600 X 900 pixels (150 X 4, 150 X 6)  For 8 X 10 print – you need at least 1200 X 1500 pixels Digital Cameras

Some cameras have multiple resolution settings (pixel dimensions) available Some cameras have multiple resolution settings (pixel dimensions) available Use lower resolutions for smaller file sizes if you don’t need to enlarge the image for printing Use lower resolutions for smaller file sizes if you don’t need to enlarge the image for printing Digital Cameras

Image Size Best to create the image at the final size you want to use Best to create the image at the final size you want to use  You can always resize images smaller without loss of quality  Resizing the image larger later can degrade image quality

Digital Cameras Digital Cameras  Start with camera set at highest resolution setting if you’ll need to print a larger image  Use image editing software to resize print dimensions/increase image resolution  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

Scanners Scanners  Set scanning resolution as high as necessary  Scan at higher resolutions for both print and online viewing for best quality  Choose the desired print dimensions before scanning  Best to scan larger and rescale smaller, than to scan small and then try and resize larger Image Size

If you’ve scanned at a higher resolution ( dpi): If you’ve scanned at a higher resolution ( dpi):  If image is to be used online, use image editing software to lower image resolution to ppi  Image detail captured by higher resolution scan will still be there, but file size will be smaller  Improves quality of images printed from Web pages Image Size

File Formats JPEG (.jpg) Joint Photographic Experts Group JPEG (.jpg) Joint Photographic Experts Group  Image is automatically compressed so file size is smaller as camera saves the image as a JPEG file  Most digital cameras use the jpg format by default  Some cameras use a proprietary file format you’ll need to convert to useable formats using image editing software

 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

Many digital cameras have different quality settings Many digital cameras have different quality settings  Hi – usually uncompressed TIFF files  Fine – lowest compression JPEG file, larger file size  Normal – more compression, smaller file size  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 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 Most scanners allow a choice of different file formats to save the final scanned image Choose the format that’s best for the intended use of the image Choose the format that’s best for the intended use of the image JPEG is best for online images due to image compression – smaller file sizs JPEG is best for online images due to image compression – smaller file sizs TIFF is often best for printing images – no image compression, no loss of data TIFF is often best for printing images – no image compression, no loss of data File Formats

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