Understanding Image Resolutionby TJ Tierney
ood photography remains as elusive and as enticing as ever -- knowing how to optimise it in your digital darkroom will only make it better.
Resolution is a term used a lot in photography these days -regardless which type of photography you do, or which type of camera you use, understanding image resolution, pixels and the different properties attributed to them is so important.
Whether you are printing, scanning or sending an image by e-mail, you need to understand and know how to keep your images sharp and preserve as much detail as possible in your final print. This topic does cause some confusion, so I hope the following will help.
Image resolution explained:
Photography resolution is a measurement of image quality, so you may define resolution by how much detail is in your print. If your print has sharp detail you may consider your image to be of good resolution. If detail is blur in your image you may consider your image to have poor resolution. Good resolution is a direct result of having a large number of pixels in an image.
Digital images are made up of millions of small dots - each dot is called a pixel. Each dot contains a small piece of image information, and when added together with the other pixels you'll get your final image.
Print resolution is measured in pixel per inch (ppi) or in dots per inch (dpi) - both hold the same value. 300ppi means that there are 300 pixels per inch or 90,000 pixels per a square inch.
What size can I print my images?
A digital image that's 1500ppi wide will print a 15-inch wide print if the print resolution is 100ppi. If you change the same image to a print resolution to 300ppi your final print size will become a 5-inch wide print.
If your image file is 3000ppi wide x 2400ppi high with a print resolution 300ppi, your final print size will be 10 x 8 inch. The same file with a print resolution of 150ppi will give you a final print of 20 x 16 inch.
Divide the print resolution into the pixel width or height of your image.
Higher resolution should not be taken to mean that your images would be of higher quality - your images would only be of high quality if you print to the correct format. Example - if you print a 3000ppi x 2400ppi size file to a print size of 20 x 16 inch at 300ppi, the pixels may be visible resulting in a blur image. You need to print it at 600ppi to attain good quality.
What size resolution should I use?
At 600ppi (which is an extremely large resolution) your image will be supreme sharp. You will be restricted with print size.
Printing your images at 300ppi is the standard quality. Image sharpness doesn't get much better. The only setback is that the maximum print size will be restricted - you might need to drop the resolution to get a larger image.
If you need a large print from a small file print your file at 150ppi - your print will lack detail and the pixels may be visible. You should not print an image any smaller than 150ppi.
72ppi is standard with your computer screen. Don't print your images at this size - the pixels will be visible.
Scan your images as large as possible; it's easy to resize them later. If you scan an image to small you may have to re-scan at a later date to get a larger print.
If you need a print that's twice the size of the original - scan it at 600ppi and print it at 300ppi.
Try to print your image at 300ppi.
If you use a tripod when taking an image you may be able to push the print resolution lower than the recommended 300ppi - this will enable you to get a larger print.
Be very careful when cropping an image, if you crop it too much you will reduce the print size.
Be careful not to confuse print resolution with printer resolution; printer resolution is measured in dots per inch (dpi), but these values are a great deal higher- common printer resolutions are 2400dpi and 5760dpi - this is a measure of the amount of ink dropped onto your paper per inch.
Call Of The Wild Photo Comments:
As TJ points out, understanding what image resolution is and how it is used by the various devices in your digital darkroom will lead to better results when you print your image.
I agree you should always scan your photos at a higher resolution to preserve the details. However, for best results, you should never exceed the optical resolution capabilities of your scanner.
I prefer the results from scanning the film or slide directly, with a dedicated film scanner, over the results of scanning the printed photograph. If you want to scan your film/slides, I have to recommend using a film scanner. Many consumer flat bed scanners have film/slide adapters, but I've never been happy with the results of those I've tried. -Anita