Subject Guides

Using Images

Citing Images, Evaluating Image Quality, Image Copyright, Digital Imaging, Finding Images

Digital Imaging

When using images in your papers or presentations, keep in mind these helpful guidelines to ensure the best image quality possible:

5 things you need to know about Imaging:


I. Pixels

A digital image is made up of a grid of pixels (picture elements)


Fannywackle/Wikimedia Commons/ CC-BY-SA-3.0


II. Resolution

Resolution is determined by how many pixels there are within the image. The higher number of pixels, the higher the resolution, and therefore the sharper an image will be. The lower the resolution, the more blurry (pixelated ) the image will be. Resolution is measured both in pixel dimensions or document size (pixels per square inch or ppi). 


For example:

Pixel dimension:

1060 x 800 pixels= 1060 width x 800=height


Document size:

300ppi=300 pixels x 300 pixels (smaller pixels, for a crisper image)

72ppi= 72 pixels x 72 pixels (larger pixels, which may blur an image)



Wikimedia Commons/ Public Domain/

Image (zoomed in to show quality), 3” x 3” at 72 ppi



Wikimedia Commons/ Public Domain/

Same image at 300 ppi, 3” x 3”


The optimal resolution for printing a digital image is typically 300 ppi, depending on how large your image is. For an 8 x 12 sheet of paper, stick with this. 600ppi resolution is used in professional printing. The human eye will not see a difference and your file size will be much larger if you go above 600ppi.


Be aware: when printing, the terminology is changed to dpi or Dots per inch. Dpi is used to refer to an output resolution of a printer. You usually don’t have to worry about this when using the latest printers, scanners, and imaging software.  Please visit the VRC if you have any questions about scanning images.


If you are giving a slide presentation, (such as PowerPoint) you can make the resolution smaller at 72 ppi-150 ppi. Using a larger resolution will make it hard to save your document as each image will take up a lot of space.


III. File Size

File size is determined by how much data is in a file, measured in kilobytes (KB) , megabytes (MB), or even gigabyte (GB), which is usually used when referring to hard drive space, not a single image.  The resolution and size of the image can change a file size.




IV. File Type  +  V. Compression


TIFF (TIF) or Tagged Image File Format. This is the preferred archival standard for digital storage. Tiffs are uncompressed, meaning all data about the image is preserved and nothing is lost.


JPG (JPEG) or Joint Photographic Experts Group. A compressed format that removes inessential data such as indistinct color tones and reduces the file to a more manageable size. Best used in papers, slide presentations, on the web, and editing images.  


PSD or Photoshop Document. An Adobe (therefore, proprietary) file. Use only when you are sure you need the image for use within an Adobe product.


GIF or Graphics Interchange Format. Use for graphics with few colors, not photographs. GIFs are 8 bit, therefore have only 256 colors. As a comparison, JPEGs and TIFFs support 24 bits, or 16,777,216  colors.



If you need help with scanning images or setting up a presentation using any type of software, such as Power Point or ARTstor OIV, please contact Marcia Focht, Curator of Visual Resources at Check the Visual Resources Collection page for more information.


For more in-depth explanation on digitizing a collection, technological specifications, and everything you’d possibly want to know about digital imaging, see this useful blog from the State Records of New South Wales or this comprehensive Getty Research Imaging Guide.