will47 Loc: Indianapolis, IN

If for instance, I decided to use a photo from a source such as Unsplash for the background of one of my photos. Possibly a portrait. Assume the background is 72dpi and my photo is 300dpi. Should I worry about the background or just continue working? Now if I was going to do a composite and the background image was going to be a main component of my finished photo and the disparity of the dpi's remains the same what should I do? Thanks.

Longshadow Loc: Audubon, PA, United States

DPI <> PPI.

I myself, would see how it looks before I worry about it.

rwilson1942 Loc: Houston, TX

DPI is a printer thing, it has no bearing on digital images.

CHG_CANON Loc: the Windy City

The logic expression above states it exactly: 'dots' have nothing to do with pixels. Your digital editor edits pixels.

will47 Loc: Indianapolis, IN

I think I understand that but, what if I plan to print what I am working on?

CHG_CANON Loc: the Windy City

You take the pixel resolution and divide your image pixels by the desired pixel per printed inch, ppi - pixels per inch. A 'gold standard' would be 300 ppi, where 6000 pixels on the long side would be 20 inches (6000px / 300ppi = 20 inches). The larger you print, the less critical a 300 ppi gold standard becomes, unless you want your viewer to stand nose to print like they could for a 5x7 print.

LindaPuyear

Hi. DPI stands for "dots per inch", meaning back in the old days when offset lithograph printing became the commercial way to print stuff, wooden frames with fine wire screens were made with standard spacing such as 50 dpi (wires per inch) or 100 dpi, etc. These screens were placed over continuous tone paintings or photographs and shot with a fixed camera, producing a film negative of the image that could then be transferred to offset lighography printing plates that could in turn be mounted on a press to print reproductions of the original images. On top of that, a separate shot for each of the 4 standard printing inks, (cyan, magenta, yellow, black) had to be shot using filters on the camera to capture each of these 4 colors on 4 separate negatives that in turn produce 4 separate printing plates. The offset press then made 4 passes to produce a complete color image. Another archaic bit of trivia, the term screen angles refers to angling the 4 screens at slightly different angles so that the tiny dots printed for each color were slightly different shaped ovals to avoid a "moray" effect caused by all perfectly circular dots. Whew. Lot of work. Yeah for digital! Now the standard is 300dpi for printing and 72dpi for viewing on a monitor, and yes, large volume printing for magazines and such still has dots and is still cmyk (cyan, magenta, yellow, black) ink on offset lithograph presses. However if you order Christmas cards printed of your family for example, those are run on short run digital presses that simply reproduce your image continuous tone on an all digital press. When you see suggestions you send in your images at 300 dpi, they are using that as a ballpark standard to avoid people providing low resolution images.

PPI is a digital measurement that stands for "pixels per inch" and refers to bit map images. 300 dpi equals 118.11 ppi. Who comes up with stuff? We do need to understand it though.

I have now forgotten your question and if have read all of this you are probably sorry you asked.

df61743 Loc: Corpus Christi, TX

The pixel dimensions of your background photo would be your only concern, and DPI is irrelevant.

When you merge the background and foreground, they become one image, that has only pixel dimensions... no DPI. When you decide you want to send it to a device (like a printer) that wants to refer to the image size in inches, rather than pixels, DPI becomes an issue.

You will crop and/or resize the digital image to fit the paper you want to print on, and save it at 300 DPI or whatever DPI you think is appropriate.

CHG_CANON said it right. Digital images are measured strictly in pixels. Printers measure that same image in inches and dots.

speters Loc: Grangeville/Idaho

I really don't know what you're getting at, you are talking about print resolutions and then you mention your photo is 300 dpi, (it is only 300 dpi, if you print it at that resolution! I guess you do not really know what dpi stands for!

Tomfl101 Loc: Mount Airy, MD

I think I understand your issue-
You will need to enlarge the smaller background layer to match the larger foreground. This may cause the background to look pixelated. If a soft background is your aim, just blur the background and it should look fine.

Hamltnblue Loc: Springfield PA

You can resemble the background at 300dpi before merging

gvarner Loc: Central Oregon Coast

Do you mean "ppi"? Dpi is used in printing and stands for dots per inch, as in dots of ink per inch. Photo files are referenced in pixels per inch. Not the same as dots of ink.

nospambob Loc: Edmond, Oklahoma

Wow, thank you Linda for that cool explanation. Cool beans!!!

coolhanduke Loc: Redondo Beach, CA

Garbage in garbage out. 72dpi is 72dpi. It will come out pixelated.

Sunrisepano Loc: West Sub of Chicago

So many people see ppi (pixels per inch) as the end all. The term has two expressions, "pixels" and "inch." Therefore, the end all is if you have the numbers for both terms.
If you have your front image of 300ppi, how many inches is it? 10? Then you have 3000 pixels to work with in the one dimension.
If you have your background image of 72ppi, how many inches is it? 10? Then you have 720 pixels for the background which is less than one fourth of the main/front image. Not good.
If your background image is 72ppi and 40 inches, that is 2880 pixels compared to 3000. Go for it. They are comparable in size.
Remember, two terms, pixels AND inches. If you have both, (you must have both), do the multiplication and you have your answer.