DPI Question - DPChallenge Forums

Sony 16-50mm f/3.5-5.6 E-mount

06/29/2005 11:19:39 PM · #1

Ok here it is-
I am shooting in RAW and I am wondering what is the largest DPI I can save to? I know I have the ability from 10-2000 but is there any reason NOT to save 2000 DPI?

Oh, BTW I have recently changed to saving as TIFF so as not to loose any pixel info. (live and learn right?)

Any insight would be appreciated!

jmsetzler

Sony Alpha a6000

06/29/2005 11:20:15 PM · #2

DPI has no relevance until you print.

Cracked Egg

Tamron AF 28-300mm f/3.5-6.3 XR Di LD Aspherical IF for Canon

06/29/2005 11:28:06 PM · #3

Well the best reason is file size. Large files take up room and are a pain to work with in photoshop. I save mine at 300 dpi which is the ideal size for printing, smaller you will lose quality and larger you are creating a large file for no reason. The key is 300 dpi at 100% of the size you want to use for printing.

kyebosh

Canon EF 80-200mm f/2.8L

06/29/2005 11:29:39 PM · #4

Originally posted by Cracked Egg:

no, this is not correct. Changing the DPI only changes the size of the print the computer thinks you are making. a 3000 x 2000 pixel image is the same quality if it's at 100dpi or 2000dpi.

Cracked Egg

Tamron AF 28-300mm f/3.5-6.3 XR Di LD Aspherical IF for Canon

06/29/2005 11:41:28 PM · #5

Kyebosh, I am talking about dots per inch, and in the printing world, which I have been in for over 20 years a 300 dpi image at 100% of the usage size is optimum for print. Try taking a 1200 dpi image to your local service bureau and it will choke their rip system. Anything smaller and you will hear "you have a low res. image in your file", which will also flag the rip system. RGB images will flag it as well. Hope this makes sense.

kyebosh

Nikon AF-S NIKKOR 24-70mm f/2.8G ED

Canon EF 80-200mm f/2.8L

06/29/2005 11:46:30 PM · #6

Originally posted by Cracked Egg:

That still doesn't make you correct. The file is the SAME SIZE if it's 1dpi or 2000dpi. The only way you change the file size is if ou increase DPI AND don't let the size adjust automatically.

edit: If i'm not being clear... I can prove it with examples if needed.

Message edited by author 2005-06-29 23:48:18.

Neil

Fujifilm X-T30

06/29/2005 11:49:05 PM · #7

If I can interpret here, I think the source of confusion here is the DPI metadata in files (kyebosh is talking about this), and the output DPI (Leonard), where you say want a 4x5 on a 300 dpi device, so you know you need to size it 1200x1500.

I always thought the DPI metadata was a bit strange, because I can set it lower and then software handles the print differently, rather than simply looking at the output device, the pixel size I supply, and the size I request for printing. I am not really sure what the dpi setting in the file is useful for, and why it was put there.

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

06/29/2005 11:51:42 PM · #8

The point is that phrase "at 100% print size."

In the offset printing world it is correct, that you don't need over 300 dpi, because those pixels are being used to create halftone dots for offset printing at limited resolutions.

In (relatively) continuous-tone photographic printing, you can put in as many DPI as you want without "choking" the processor -- also, the files are left in RGB mode instead of being converted to CMYK.

So, in the photo words, at least capturing the maximum number of pixels (regardless of what dpi value they are assigned) is almost always a good idea. You can easily throw out unneeded data, but can't "recover" what was never there.

BTW: In offset printing, 1200 dpi is just dandy for line art -- my imagesetter goes up to 3600 dpi. 300 is the optimum value if you're using a 150 LPI (Lines-Per-Inch) halftone screen, and modern RIPS don't really care about overly high-res images any more.

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

06/29/2005 11:56:59 PM · #9

The dpi value is there to do just what it says: to tell the software how many pixels (dots) to display per each inch of target devise (printer, monitor, whatever).

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

06/29/2005 11:59:16 PM · #10

You can drive at ten miles per hour for ten hours, or a hundred miles per hour for one hour, and have the same number of miles driven -- 100.

If you have 1000 pixels, you can display them 10 inches across at 100 dpi or 1 inch across at 1000 dpi.

Nikon AF-S NIKKOR 24-70mm f/2.8G ED

06/30/2005 12:12:50 AM · #11

But when converting from RAW it doesn't let me decide output size, only DPI It automatically does that for you? ...now I have to go check out the differences!

Neil

Fujifilm X-T30

06/30/2005 12:15:25 AM · #12

Originally posted by GeneralE:

Yes, I take it back. I see that it's used to keep the output size as planned, despite the resolution of the output device.

I have 1000 pixels and the file is captured at 200 dpi. Without the dpi setting, it would be 10 inches on a 100 dpi printer, and with the DPI setting, it prints it 5 inches across. If I switch to a 200 dpi printer, it will still be 5 inches across.

Unless I tell it to print 1:1, in which case it prints 10" across on the 100 dpi printer, and 5" across on the 200 dpi printer.

Still, I'm not sure what a dpi setting means in a photograph. What does 300 dpi mean as captured on a CCD? Trying to maintain some semblance of scale?

06/30/2005 12:22:22 AM · #13

Originally posted by nshapiro:

Still, I'm not sure what a dpi setting means in a photograph. What does 300 dpi mean as captured on a CCD? Trying to maintain some semblance of scale?

While your explanations make me seem to understand it more, that leaves me with the same question?!? whether I output 400dpi or 800dpi the file size and pixels stay the same while only the dimensions change- therefore it seems arbitrary, right?

Message edited by author 2005-06-30 00:23:23.

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

06/30/2005 12:41:12 AM · #14

OK, a CCD sensor is about 1/2 or 2/3 inch across, with something like 2-3000 sensors, so you can see the density of the CCD bears little resemblance to the output dpi figures. What you really need to know is how many pixels your camera captures; from there the output dimensions and the dpi value are just simple math.

kyebosh

Canon EF 80-200mm f/2.8L

06/30/2005 12:47:56 AM · #15

edit: I think i'm tired >_<

Message edited by author 2005-06-30 00:49:39.

06/30/2005 12:57:15 AM · #16

Originally posted by GeneralE:

So I could go 72 dpi or 1200 dpi and it's all the same thing coming out the same camera- right?

pixieland

Fujifilm FinePix S602Z

06/30/2005 12:58:05 AM · #17

This may be irrevalent to the answer but isn't it called ppi(pixels per inch) going in and dpi (dots per inch) going out to print?

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

06/30/2005 01:24:09 AM · #18

DPI is used for almost everything. In the printing industry, you can have:

ppi = pixels per inch -- in the file

dpi = the size of the smallest dot the printer can make

lpi = lines per inch -- used in offset printing to describe halftone dots

Think of pixels as little electronic mosaic tiles -- they can be bigger or smaller, but can't be broken into pieces. If you are going to make a mosaic 1 foot square, you can make your image have a lot of detail if you use tiles 1/4" square (48 tiles per foot) than if you use tiles 2" square (6 tiles per foot).

However, you can take those same 48 tiles and make them 2" and end up with an image 8 feet square (also at 6 pixels/foot) ...

When you resample an image to make it bigger, you essentially spread the tiles farther apart, and then make new ones to fill in the spaces; each new one based on some average of the values of the surrounding ones.

pixieland

Fujifilm FinePix S602Z

06/30/2005 01:37:01 AM · #19

Thanks GeneralE,I am just learning this stuff, even though I took some Graphic design classes a couple of years ago, good thing I didn't have to pay for the course cause they left alot of stuff like this out.