DPI (Dots Per Inch) and
PPI (Pixels Per Inch)
When talking about the inking of prints DPI means Dots Per Inch. Just to make everyone confused DPI is also sometimes used to refer to Pixels Per Inch.
To be technically correct we should really refer to resolution as PPI or px/inch or px/cm. The DPI of an image is not what makes the quality of a print. The resolution quality of an image is its pixels (megapixels).
Here are some factors that effect the quality of an image:
1. The size (pixels) - higher is better
2. The quality of the recording device (like a camera’s optics and sensors)
3. The file format it is stored in
4. The technical proficiency of the photographer
There can be many other factors.
If the number of pixels do not change in image editing software, it really doesn’t matter what the DPI/PPI is set to. It won’t change the quality of the image. Some printers will only accept a resolution between 200 and 300 in order for it to believe the image is of photographic quality.
So again, if the number of pixels of an image do not change, then it has the same digital resolution no matter what number is parked in the DPI/PPI setting of the photo.
Scanning a photo and DPI:
If you need to print a 4x6 photo at it's original size, you would scan it at 300 DPI. If you need to print it at a larger size, like an 8x10 photo, you would need to scan it at 600 DPI.
Keep in mind not all devices are capable of doing this.
Meeting Print Shop demands:
Using the 300 PPI criteria, if the image is to be printed 7 inches in size, then your digital image has to be a minimum of 2,100 pixels in that dimension (2100 pixels / 300 PPI = 7 inches)
Print shops and designers need to be careful not to reject a perfectly suitable photo because the DPI/PPI setting in the photo is not 300. A photo that is 1500 x 2100 pixels in size with a DPI/PPI setting of 72 (the default in most digital cameras) will print to 5" x 7" at 300 PPI. Putting it another way, at 5" x 7" it is a 300 PPI photo (no matter what the internal DPI/PPI setting is).
I hope this helps you to understand the often confused meaning of DPI/PPI
Images used can be found at iCLIPART.com
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