PPI vs. DPI

In the case you're referring to, people are usuing dpi and ppi interchangeably. It may not be technically accurate, but it is very common to use the term dpi when discussing file resolution.

The distinction people usually make here is that dpi referrs to the actual number of dots laid down on the paper. In other words, dpi is really an output setting that isn't a reflection of the resolution in the image itself. For example, inkjets often use dpi settings of 1440, 2880, or 5760. These don't necessarily correspond to the file's ppi, but rather are a reflection of the many small dots laid down to make up each pixel of color.

PPI, in turn, is the number of discrete pixels of (possibly) different color in the file. This is the image's resolution. What they are looking for is a file that is at least 1200x1500 pixels across. If you are resizing the image to 4x5 and it is 70ppi in PS, your file is 280x350 pixels across and will not print well at 4x5. If you shot it large, then only having 280 pixels across seems unlikely. Hope that helps a little.

These two terms basically mean the same thing. Dots or Pixels per inch. If they require a photograph to be 4x5 at 300dpi then they are asking for images that are at least 1200x1500 pixels.

They definitely do not mean the same thing. Listen to Marshall.

Without getting overly technical about this, think of it this way. Electronic devices like cameras and LCD displays have discrete, individual, picture elements (pixels) that either receive (cameras) or display (LCDs) light at each pixel.

Printers (output devices) display images by making the images into dots. The more dots per inch (DPI) the finer the image is rendered.

It's really a bit more complicated with computer output devices as the original definition of DPI relates to printing presses and how finely a continuous tone image is screened. You really had xxx dots per inch that you could count if you used a magnifying loupe on a printing plate or in the final printed image. You can see this on a laserjet printed photo image, as those printers use physical dots per inch.

Today, inkjets and LighJet type printers really don't print in "dpi" but, it's a convenient way to summarize the amount of data being sent to the output device for it to interpolate into the final image.

As to your 70 dpi question versus 300 dpi required output, you don't give any information as to the original image size in pixels per inch (2000 x 3200 for example) other than saying "very large" - which is meaningless.

Your controls in the resize image menu should allow you to set the dpi, and the image size. Uncheck the resample box, and resize the image to 4x5 inches and see how many dpi it shows. If it's not 300 then you need to resample the image. Check the "resample" box - use "bicubic sharper" for the image if it needs to be reduced in dpi -from 600 -> 300 for example. Use "bicubic smoother" if it needs to be resampled upwards 180 -> 300, for example.

These two terms basically mean the same thing. Dots or Pixels per inch. If they require a photograph to be 4x5 at 300dpi then they are asking for images that are at least 1200x1500 pixels.

Technically dpi and ppi are not the same thing, But yes they are asking for an image that is 1200 x 1500 pixels. (4x300 pixels = 1200 pixels, 5 x 300 = 1500pixels.

What camera are you using? Go back to your original image. In Photoshop, Go: Image> Image Size > and uncheck Resample Image. this will link resolution (PPI) and height and width. enter 300 as resolution. What size in inches d oyou get as height and width?

"Electronic devices like cameras.............."

LOL! Don't you mean "Digital cameras?" Can't find the battries in my Leica M3.

take your original image unresized and do the following:
first using the image resize tool, uncheck the resample box at the bottom.
Then, and only after unchecking the resample box, set the resolution box to 300 pixels/inch and press OK.
Next save your image.
Next open it again and using the image resize tool do the following:
check the resample box
set the resample type to bicubic.
check the constrain proportions box
Next depends on whether original image was portrait or landscape:
If image is landscape then:
set image width to 1500 pixels (height will change automatically).
if height is now less than 1200 then set height to 1200 (width will change automatically).
press OK.

If image is portrait then:
set image width to 1200 pixels (height will change automatically).
if height is now less than 1500 then set height to 1500 (width will change automatically).
press OK.

you will now have an image which needs either width or height cropping(using the crop tool) depending on the original image width:height ratios. i.e. if original w:h ratio wasn't 5:4 or 4:5 then you will need to crop to that ratio.

after this use the image resize tool to check all is OK. just change the document size to read in inches and it should say 5x4 inches with the dpi setting at 300dpi.

Thanks for everyone's input. I'm shooting with a Canon 20D set at Large/Fine, so if I'm thinking correctly, that's a 3504 x 2336 pixels image, right? If that info helps out any more towards a solution, let me know.

When I get home tonight (at the day job right now), I'll open up Photoshop and try out the solutions a couple of you have provided. I really appreciate everyone's help with this and for not making me feel like a complete gomer (dork).

:) Kristi

"My red dog can read and read a red book yesterday". A perfectly clear sentence to a native English speaker but hard to decode for someone else. Context is the key. If someone is talking about image files in, or being made by, cameras or computers or scanners then ppi is what is meant even if dpi is used. Inkjet printers create images with dots of ink, up to thousands per inch. Epson printers (mine at least) prefer files at 360 ppi. So I might say, if I'm being a bit casual, "my Epson prints at 2880 dpi and likes 360 dpi images." What I mean in the second instance is ppi. Each pixel is printed with many many dots thus creating the impression of a continuous-tone photograph.

Two other points: pixels have no size at all; they are just data. The physical size of an image (e.g., 4x5 inches) is just a instruction to the printer like telling the printer that a landscape (horizontal) image is on its way. But print size and ppi definitely interrelate. Open any image and play with the Photoshop Image Size dialog. Leave the "constrain proportions" box checked and play with the "resample image" checked and unchecked. You'll see what's happening.

If resampling is off and you double the document size, the ppi is cut in half. That is, you're stretching x number of pixels to twice one length of the document, there will half as many per inch as there were. That is OK only if there is still high enough ppi for your printer--360 ppi in my case. Conversely, with resampling on if you double the document size the ppi stays the same but the file size grows four times larger. Where is that extra data coming from? Photoshop is creating more pixels as best it can. That too may be OK depending on the print size. In your example of 4x5, that is so small that up sampling may not be noticeable. But with your example of printing to 4x5 inches with only 70 ppi--well, there is not much hope for such an image. So I am not sure what you mean in saying "they were shot very large." What happens if you up sample? What are the original file pixel dimensions?