# Photo Contest Help



## timmy_650 (Jan 11, 2018)

My wife is working at a new medical school and they want to have a photo contest for the students. They were wondering about files sizes and printing. They want to be able to print on metal at 24 x 36. 

The wording the put in the email to my wife and asked her to ask me is

"Electronic file must be a minimum size of 4mb at 300 dpi and a maximum of 15 mb size."

Do you think a 4mb file will be big enough to print at 24x36 and still look good.


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## Mikehit (Jan 11, 2018)

The problem with 'acceptable' image quality is that people see an image and want to walk up, look at it from 6" and see every hair and pore. When in fact in real life they would stand at least 4 feet from an image 24"x36"

You should be able to print a 4MB image to about that size provided you don't have to stand too close - I have 600X 800 pixel jpeg image (300kb size) to A3 OK. Printing overcomes a lot of sins that are obvious on screen. 


By the way '300 dpi' is irrelevant when referring to file size size because dpi is only relevant for converting to print. Do the maths:
At 300 dpi at 24x36 = 7,000 x 10,000 dots. If you print at what can loosely be called '100%' (as it is on screen) that is a 70MB image. 

For some reason, 300dpi has become a default printing requirements but many people more experienced than I say you can hardly tell the difference between 300dpi and 180 dpi.


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## timmy_650 (Jan 11, 2018)

I was kinda thinking the 300 dpi was weird. It sounded like they google search for printing and saw that number and included it B/c in the email they didn't say size. 

So to me if you just put 4mb and 300 dpi....all 4mb files are 300 dpi if you don't include a size, it might be a 2 x 3.


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## LDS (Jan 11, 2018)

Mikehit said:


> For some reason, 300dpi has become a default printing requirements but many people more experienced than I say you can hardly tell the difference between 300dpi and 180 dpi.



That's because printing at 133/150lpi on an half-tone printer (common resolutions for magazines, etc.) requires an image with a resolution of 300ppi (actually 266 for 133lpi, but 300 will work too).

When a pixel and a dot are the same (i.e. most image file formats, screens), it's also 300dpi.

The formula is lpi x 2, or lpi x 1.5 if a little lower quality is acceptable. Beyond 2x multiplier, any added resolution is wasted on halftone printers.


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## hne (Jan 11, 2018)

I sure hope the specification of file size being between four millibit and 15 millibit was a typo.

Let me send in a few 300x450 pixel files "compressed" to 10MB size, with some embedded metadata stating that they are 1"x1½" in size, that is... 300dpi. No problemos!

No, you can't specify a lowest file size for a compressed file and assume that'd say anything about the quality. That is insane. I've got lots of files at under a megabyte that look fantastic blown up big and several files over 10MB that just look ugly if you print them larger than postcard-sized because of all the distracting fine detail.

I would specify a list of acceptable file formats, a minimum expected pixel dimension of about 2400x3600 and a warning that too much compression or low number of pixels will cause the prints to look bad, lowering the chances of winning. Possibly also a line on any technical restriction in maximum file size accepted for submissions, eg "no larger than 100MB per file".


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