The physical size is determined by the size pixel you print. The image Aspect ratio is determined by the number of pixels you have width and height. To change an images Aspect Ratio you have two choices Crop or Distort the image.
Pixel density 300dpi pixels are printed 1/300"x1/300= 90,000 pixels per square inch 72Dpi pixels are 1/72"x1/72" 5,184 pixel per square inch. The 300dpi print will be much smaler and sharper then the 72dpi print.
I actually just figured it out... it was in "Workflow Options." However, it seems that I cannot keep the large physical size with 300dpi, as changing that setting to 300 is what knocked down the physical size by default. Which makes sense, I guess.
This brings me to a new question... If I go ahead and open the photos at 72/default size (somewhere around 44 inches) and I want to create a print ready photo at say 20 inches 300 dpi... What is the proper way to resize the photo and set the resolution resampling, etc. I realize that when I do not check off "resample" and I change the dpi to 300, the image is back at only 15 inches. So, to keep physical size relatively large and set resolution to 300dpi, what should I do? I am sure there are other forums about this, but I thought it was worth asking anyway.
Also, thank you for your quick response!
Why is 300DPI important to you. Printers can print any size pixel you need to print the image the size you want your print to have. Do not lose image quality by resembling your camera image. Why are you concerned with DPI resolution you need to be concerned about the pixels you have for you image. The pixels you get from your camera are the best pixels you will ever have for you image. You do not want to change the number of pixels you have except when you need to save small Web image for displays can not change their spots.
Use Image size do NOT check RESAMPLE set the print width or height you want you print to have. Photoshop will the set the other side length and the correct pixel size to print with. Print DPI Resolution is just a setting that set the pixel size the image will be printed with.
When RESAMPLE is NOT checked the numbers of pixels dose not change Not a single pixel is changed all that changes is the print Pixel Size. The Print Dp resolution is just a setting the is easly changed.
From what I understand, 300 dpi is standard for print. 72 is standard for screen. I want a high-res image so that it prints as clear as possible for a large sized print. I guess you are just saying that I should start with the default dimensions (around 44 inches) and down size it to whatever I want using "Image Size," while leaving the resolution at 72. I get that but that doesn't help me get a large print at 300 ppi, which is the standard print res.
No - forget 300dpi for print. Larger prints are viewed from further away so the image pixels can get larger without being noticed.
What is being said is adjust the image dimensions for print but do not check resample. The ppi number in the image size box will change as the physical size changes - the smaller the physical dimensions the higher the ppi . Don't worry about that - the number of pixels making up the image will remain the same.
Do no think in inches - think in pixels. A 50D produces image 3168 x 4752 pixels. Prints are what have inches. The resolution is just a ratio: The pixels [of the image] per [divided by] the inches [in the print]. As JJ has said, use Image Size with Resample UN-checked.
Note that in both of these screenshots, the dimensions [of the image] have not changed, because there is no resampling. Enter your desired print size in the Width or Height fields [in inches or centimeters or whatever], and the resolution will follow.