Snagit (Windows): Effect of changing DPI on capture quality

SnagIt has a feature that allows you to change DPI of the image that you capture.  However, changing the DPI does not change the quality of the image, it only makes it print smaller. DPI in relation to screen captures is one of the most complicated aspects of screen capture.

First, it is important to define the two key terms.

Pixels

If you look closely at your monitor, you will be able to pick out small squares of color within each object on your screen.  These small squares, referred to as pixels, make up the images on your screen.

Dots per inch (DPI)

This can often be replaced with the acronym PPI, which stands for pixels per inch.  When referring to DPI, a single pixel in an image is one dot.  So, each dot printed on paper represents one pixel within your image.  The DPI setting allows a user to define how many of these dots will fit into an inch on the page.  DPI is also often referred to as printing resolution.

SnagIt will capture exactly the pixels that are being displayed on your screen.  When initially capturing images from the screen, DPI does not yet come into play.  Once you have the image captured, you can then set a DPI for the capture, so that it will print at that specific DPI.  However, changing the DPI setting does not add or remove any pixels to the captured image.  Changing the DPI will only change how many dots (pixels) will be printed within an inch on the page.  Because of this relationship, increasing the DPI for an image will make it print smaller.  This is explained by the following formula:

Image Size/DPI = Printed Size

 For example, if you have a 100x100 pixel image that is being printed at 100 DPI, the image would then be 1 inch by 1 inch when printed.  If you have a 300x300 pixel image being printed at 100 DPI, the image would then be 3 inches by 3 inches when printed.  If you had an image that was 300x300 pixels being printed at 300 DPI, it would print at 1 inch by 1 inch. 

However, if you had a 300x300 pixel image being printed at 300 DPI, but you wanted it to be 3 inches by 3 inches, it would not be possible.  If you enter these numbers into the above formula, they would not calculate to a print size of 3 inches, as illustrated below:

300 pixels/300 DPI = 1 inch.

In order to print this image at 3 inches with 300 DPI, first it would need to be enlarged such that when dividing the image size by the DPI, you would get a printed size of 3 inches.  This means that your image size would need to be increased to 900 pixels, since 900 divided by 300 DPI would generate a print size of 3 inches:

900 pixels/300 DPI = 3 inches.

One of the most important things to remember is that when you are using SnagIt, you are capturing exactly what is on your screen.  You can not capture more than what is being displayed.  However, you can scale what you have captured to a larger size.  You can then print the image at a higher resolution to get your desired print size.

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