# Thread: DPI - Enlarging photos ? ?

1. ## DPI - Enlarging photos ? ?

Got a photo (19.5cm x 11cm), and when I try to save as 300 dpi, the photo size enlarges by quite a lot ! ! I thought that by increasing the dpi, it just increased the dots per inch, not the physical size of the photo - am I wrong ?

Chris.

2. Hi Chris

Is it a physical photo that you are scanning??? If so you will find that scanners will always produce a very large file with HUGE dimensions which you will have to resize later.

Chris

3. DPI refers to the physical dot density of an image when it is reproduced as a real physical entity.

A digitally stored image has no inherent physical dimensions, measured in inches or centimetres.

Some digital file formats record a DPI value, or more commonly a PPI (pixels per inch) value, which is to be used when printing the image. This number lets the printer know the intended size of the image, or in the case of scanned images, the size of the original scanned object.

Here is my calculation:
1'' = 2.54cm; we will have 300 pixels at every inch ->

[ 7.7 x 4.3 = 33.11 sq.inches ] x [ 300 x 300 ] = close to = [ 2300px x 1300px ]

Needless to say, DPI has everything to do with file size; even a seemingly thumbnail picture may have enough depth (resolution) to let you focus inside a hundred times ( Alice's hole ).

Or, may be, a lot more!

We see the stars above during all night, don't we? Always big and shining, but merely just one pixel to us. Assuming what you see is captured in a small frame of inches, using your fingers to make a rectangle and there you'll have one.

In this case the DPI is what your eyes see. Believing that you can count every 'bright dots' inside the frame, the DPI is quite limited!

But how about taking another 'resolution check' with a much better 'eye' - here let's try one and pick your "dot". You're on the house.

See? that dot has a good chance of being just another galaxy! Waving a hello to Alice, we are lost inside your thumbnail beyond imagination!

Seeing that the real world has infinite DPI, you must also agree they stored infinite information.
Should the DPI be limited, so would be your file size.

I believe my point is taken.

4. hey, sorry if i am hijacking this thread but it is reasonably relevant...

i have been working on a poster for a social a local church is throwing. They have requested that it needs to a size equivilent to A3 which i looked up is about 297mm(w) X 420mm(h) @ 300dpi

i tried working in this format but i was torturing my computer so reduced the dpi down to 150.. this has given me a resolution of 1753x2479 pixels..

will this still be the correct measurements and resolution for a A3 print?

after reading this, it sounds like i have reduced it down to A4 by halving the dpi...

if this is true, what will be the outcome if i just put it back up to 300dpi through image resizing?
hope to hear good news.. thanks...

i use GIMP not Photoshop...

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