72dpi - resolution - resampling - dpi - ppi

[tomorrowstreasures]

So, I shot in camera raw + jpeg lg... reviewing the jpeg files in Adobe Bridge - it says 72dpi.... WHAT???? I thought I would be getting the 300dpi... can anyone help me understand this?

[jjeling]

I think all jpeg files recorded by camera's are recorded in 72dpi. I think it is something you have to do in PP. My Pentax and my Sony record all the jpegs in 72dpi. Maybe I am wrong, but thats what my experiences have told me.

[kat]

This is a great question.

I tried the Raw+JPeg and couldn't get the Raw to upload and the JPeg was low dpi. Can't remember what, it was a while ago.

I've also notice that I have some images pop up at 240 dpi and others 300 dpi. And I haven't changed the settings on my camera for the last year (nor the computer - but then again, we do have two and I use both).

I'm curious to know...

[Gatepc]

I dont mean to be rude ( and i could be wrong so correct me ) but dpi is only a measurement that tells a device how big to display or print something and does not mean anything!!!! since the only thing that matters is resolotion when you go to print it it will STILL print at 300 dpi ( or what ever your printer prints at ) its only a guideline so to speak for devices which doisint really matter anyway.

a image at 3600x2700 res and saying 72dpi on the exif will give you identical results to file with the same res saying 5000dpi becouse the printer recognizes that this "size guidline" is false and writes its own before printing


sorry for spelling using touch screen device

[Iguanasan]

According to Page 170 of the owner's manual you should get the following resolutions:



Now, if I understand this correctly, DPI is dots per inch and whether it's 300DPI or 72DPI will depend upon how big the resulting photo is when it is displayed or printed. If you print the photo on a 4x6 and you do not lose any of the pixels then you are going to get

4368 / 6 = 728 DPI horizontal resolution
2912 / 4 = 728 DPI vertical resolution

So you are at 728 DPI.

That same photo printed at 8 x 12 will get you

4368 / 12 = 364 DPI horizontal resolution
2912 / 8 = 364 DPI vertical resolution

This is 364 DPI.

Remember, no matter what we do the image only has 4368 horizontal dots and 2912 vertical dots. The more inches that it's spread across the smaller the DPI.

Computer screens are generally 72 DPI because that's the largest number of pixels they can fit into 1 inch worth of screen "real estate". Note that newer monitors can go higher (96 and 120) and you can see the DPI of your screen in the advanced display properties (in Windows).

To make a long story short, you might be seeing the display properties of your image showing 72 DPI because it's being displayed on your monitor which really has little to do with the DPI of the image since that is completely dependent upon how big it is when you print it.

[tomorrowstreasures]

Nice that I read these replies on Valentine's day so I can say Love you guys with out too much brow raising!

Thanks for all of the feedback! !!! ! Very,very helpful!

[mindforge]

DPI is a screen and printing term. Dots per inch. It has nothing really to do with the images in your camera. Even the lowest can run at 300dpi at size and look good.

72 DPI = Screen Resolution
172 DPI = Newspaper images (highest quality papers) Keep in mind that most newspapers now have ink optimizers that cut down on the dpi on the plate so they use less ink. So newspapers can print 100 dpi on some plates and 172 on others. DPI is just a term for formatting images for internet use 72-120 DPI and formatting for printing.
200-300 dpi = most trade magazines
300 dpi = high quality printing


Also, if you have a printer capable of printing higher than 300 - you can't see the difference, even at 600 dpi. The only reason you would ever print at high DPI is large format imaging and only if you shooting with a FF camera.

[ridicwilco]

actually, dpi does matter. here's an example why: if you scan an object on a flat bed scanner at 300 dpi then you can print that image with a higher level of detail at 20x30in than if you were to scan that same object at 72 dpi, convert it to 300dpi and print it out as 20x30in.

when you change the dpi of an image the file size return is larger. that's because you're adding more information.

you have to think about it in terms of information vs detail

more detail means more information but more information doesn't necessarily mean more detail. yes more detail, but more of the SAME details.

say you change a 72dpi image to 300dpi. you're literally multiplying the same information to make for a larger image vs an actual 300dpi image which has a more diverse information matrix.

[Alex Wilson]

Some good info here, and I thought I'd chime in:

- Most of the time DPI and PPI are used interchangeably when talking about the pixel resolution -- the exception being when talking about the resolution of a printer. For printers, the DPI output is talking about how small the dots are it uses to make the image. In that case, it is not the same thing, since it take many dots over a larger area to render a single pixel of the source image. If you've got a 1440 DPI printer, you don't want to print your images at 1440 PPI on it.

- On a scanner, the PPI is very important since what you're scanning is of a fixed size. Being able to double the PPI means a higher resolution image.

- For an image file, PPI means absolutely nothing unless paired with the image dimensions. A 300 PPI 8x10in file contains exactly the same information as a 75 PPI 32x40in file.

So why do you need to know or care about PPI for an image?

Photoshop and other image applications will use it for printing. If you've set the PPI (or the setting has carried through from your raw file) then that's the size it will print at -- unless you override the print setting to scale it to fit to the paper, etc.

It also makes it easier when talking about printing formats and such. For the print shop I take all my stuff to, it's much easier for them to say to provide the files at 300 PPI rather than list the pixel dimensions of every possible image size.

[Marko]

I don't think so T.I., I only shoot RAW and this happens to me too.

I guess what I was referring to more precisely is the opening up of an image, in my case using camera RAW or the Bridge part of photoshop which is similar to lightroom. And I only shoot in RAW.

When I double click an image to open it sometimes the image has a default size (which of course can be easily changed) of 240 DPI. Sometimes it has a default size of 300 DPI.

The question is why is this DPI not consistent when opening the image in camera RAW or Bridge. This is a bit of a hassle because people (myself included) may not realize that the image is 240 DPI when 300 DPI was desired, after it is opened in a graphics program. (In my case - Photoshop)

many thanks again for this good and informative thread