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How many equals what - dpi, mb, kb...


12 years 7 months ago #142551 by icepics
If I know an image (that I scanned in) is for example 1400 x 2100 and 590 kb, how would I know how many dpi it is? It's a photo that I did in the darkroom, it was not taken w/a digital camera. And keep it simple!! :huh: - thanks.
Sharon
Photo Comments
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12 years 7 months ago - 12 years 7 months ago #142559 by MLKstudios
Ignore kb for now.

Your image has 1400 pixels (or DOTS) on one edge by 2100 pixels on the other. It can be shrunk to make more DOTS PER INCH, or enlarged to make less.

For example, if you make it 300 DPI, it becomes 4.6666666 x 7 inches. 1400÷300 by 2100÷300.

If you choose 150 DPI, you divide by 150 instead (roughly 9x14 inches). DPI is not a constant. It's a variable.

The pixel dimensions are all that matters. 1400 x 2100 = 2,940,000 total pixels (or dots) that make up the image -- roughly a 3mp image. Pixels are the grain in a digital image.

Clear?
Matthew L Kees
MLK Studios Photography School
www.MLKstudios.com
[email protected]
"Every artist, was once an amateur"
,
12 years 7 months ago - 12 years 7 months ago #142631 by KCook
Kb is a whole other "measure", as it is the size of the data in the file for the image. Simplest case would be a lossless file, which means each pixel in the image gets its own private data set within the file. With 48-bit color depth, this results in quite a large file. Such file formats are PNG, RAW, and TIFF. A more general purpose file like TIFF can get enormous if it is multi-page (layered). The common JPG files use image compression, not a one-to-one data set. Strong compression results in a tiny file, especially compared to a lossless RAW file.

Short version: Kb is also highly variable, if you allow all the various file types.

no help Kelly
Canon 50D, Olympus PL2
kellycook.zenfolio.com/
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12 years 7 months ago #142635 by MLKstudios
No, that was really good Kelly. It shows there is no one-to-one relationship to be found. It just isn't there, so don't bother looking.

:)
Matthew L Kees
MLK Studios Photography School
www.MLKstudios.com
[email protected]
"Every artist, was once an amateur"
,
12 years 7 months ago #142645 by KCook
It's my curse (retired computer programmer) :toocrazy:
Canon 50D, Olympus PL2
kellycook.zenfolio.com/
,
12 years 7 months ago - 12 years 7 months ago #142646 by MLKstudios
I started out as an EE. Worked for DEC on PDP-11's and VAX 11-780's. Ran VMS and UNIX operating systems.

Glad I don't work there no mo'. ;)
Matthew L Kees
MLK Studios Photography School
www.MLKstudios.com
[email protected]
"Every artist, was once an amateur"
,
12 years 7 months ago #142707 by icepics
As mud.

I'm kidding, I think I understand what you're saying. I was wondering if I wanted to submit something and the requirement was max 300 dpi, how I would determine that from the dimensions of the photo. I think I can figure it out now even though it involves math...

Thanks 'some help after all' Kelly, for what I'm working on I don't need to worry about kb after all.

I think I'll go back to looking at my new book 'Camera Work' and see what was happening in 1906.
Sharon
Photo Comments
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12 years 7 months ago - 12 years 7 months ago #142708 by MLKstudios
They had tabulating machines back then. The first computer was used for the census in 1890 (I think).

I calculated 300 DPI for you above -- roughly an image 4.7 x 7 inches. You can also increase that (in size) and fill in the missing pixels with interpolated ones. It basically fills in the dots with what it figures the color should be.

Enjoy your reading/viewing of Camera Work. It is another world, and Alfred takes us there so well.

:)
Matthew L Kees
MLK Studios Photography School
www.MLKstudios.com
[email protected]
"Every artist, was once an amateur"
,
12 years 7 months ago #142710 by icepics
Oh no don't tell me that, I'm trying to escape the digital world! Yeah just glanced thru the book and it's wonderful. Wow, those are some photos. I never realized that early that someone had the foresight to see photography as art.

Thanks, the images need to be under 8" so they should work as is. The exact sizes are 1916 x 1323 and 1436 x 2117. It's for a local art gallery submission.

OK I need a calculator. And some chocolate. Or maybe a toasty bagel would be nice, it's getting chilly again tonight here in the midwest.
Sharon
Photo Comments
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12 years 7 months ago - 12 years 7 months ago #142764 by KCook
Erm, any photo editing program will perform these calculations for you, automatically. With most editors the Image menu will include the function Resize. Go to resize and that page will display your current image resolution and DPI. The image resolution will be in either pixels or inches or millimeters (sometimes your choice of 2 of those). Set the resolution fields to the inches unit. If the size shown is too big, then increase the DPI value until it shows the inches you want. Vice versa of course if the size is too small.

lazy Kelly
Canon 50D, Olympus PL2
kellycook.zenfolio.com/
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12 years 7 months ago #142770 by icepics
I may try that. I wouldn't be surprised to find out I'm reinventing the wheel. I think my image size will work, they'd be under the 8" requirement. The funny thing is, I'm having to do this to submit images via email which if accepted I'll be matting and framing my original darkroom prints. Go figure.
Sharon
Photo Comments
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12 years 7 months ago #142788 by KCook
That does sound odd. Unless they are running off their own proof prints and don't want to be fussed with adjusting the DPI. Or they are simply ignorant about how photo sizing works.
Canon 50D, Olympus PL2
kellycook.zenfolio.com/
,
12 years 7 months ago - 12 years 7 months ago #142792 by MLKstudios
Sounds to me like they want a decent size for print, but not so big they fill up their hard drives with all the contestants work.

3mp is good enough for most situations. You only need more for really large prints.

They may only plan to print small.
Matthew L Kees
MLK Studios Photography School
www.MLKstudios.com
[email protected]
"Every artist, was once an amateur"
,
12 years 7 months ago #142963 by icepics
It may be because when you submit images you are agreeing to allow them to potentially use your photos to promote the exhibit; perhaps they want a specific size to work for their newsletter, exhibit materials etc. The call for entries is to supplement a photography exhibit they host annually; it's done by the local ASMP chapter and tours the region throughout the year.
Sharon
Photo Comments
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12 years 7 months ago #142975 by KCook
I'm getting confused myself . . .

the requirement was max 300 dpi

If that is their requirement, it makes very little sense. If it is you who is making this the requirement, then is it you who is complicating the question. Dpi is of interest only for printing, and it can be very easily adjusted at the time of printing, without making any change in the resolution (pixel size) of the image being printed.

Kelly
Canon 50D, Olympus PL2
kellycook.zenfolio.com/
,

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