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For a photographer, designer, advertising agency, publisher or printer, ‘300dpi’ is not an alien term, it is a kind of prerequisite for submission of photographs. From entering a photography contest to submitting images after a professional photo shoot, one comes across this term very often. For most of the people in the industry, 300dpi means high resolution but is it the right equation to describe the resolution of a photograph ?
In the current scenario 300dpi is the most misused term, it is rather incorrect, outdated and incomplete.
DPI is abbreviation for Dots Per Inch, a term which is related to printer dots per inch.
The resolution of a photograph is ascertained by pixels. Pixels are the square, solid colored smallest element of an image file. Camera manufacturers highlight MP-MegaPixels to describe the quality of sensor in the camera.
Megapixels mean million pixels, a 10mp sensor has 10 million pixels which is calculated by multiplying the horizontal pixel dimension with the vertical pixel dimension.
A 10 megapixel photo is 3872 pixels wide by 2592 pixels high
(3872 x 2592 = 10,036,224 pixels = 10 megapixels)
An 18 megapixel photo is 5184 pixels wide by 3456 pixels high
(5184 x 3456 = 17,915,904 pixels = 18 megapixels)
A camera does not give output in dots, only pixels are relevant in a digital image. When the term DPI is used, it really mean Pixels Per Inch or PPI.
When it comes to printing a photograph, even 300ppi is not the complete term, it does not mean anything unless accompanied by the size of the print.
A 6 inches by 4 inches at 300ppi will have 1800 by 1200 pixels ( 6×300 by 4×300) or 2.16mp (1800×1200). A same print at 100ppi will be 600 by 400 pixels and at 200ppi will be 1200 by 800 pixels.
A 12×8 inches print at 300 dpi will be 3600×2400 pixels or 8.64mp
A camera with a resolution of 24.2MP is able to record an image which contains a total of 24160256 pixels. Shot in an image ratio of 3:2 a 24.2MP image would have a resolution of 6016 x 4016 pixels. With this resolution, a print size of 20.05×13.38 inches is possible at 300ppi. At 200ppi the print size will be 30×20 inches and 60×40 inches at 100ppi. At 72ppi the maximum print size without any quality loss can be printed which will be 83.55×55.77 inches with this sensor. Below 72ppi, the print quality will start deteriorating but again it depends on viewing distance, sometimes the big hoardings which are placed at a distance are printed at lower than 72ppi.
So next time if you come across 300dpi ask for print size and do not forget to point out the difference between dpi and ppi.
© Ravi Dhingra