How do I go from 72 to 300 ppi?

[dave_powell2]

Hi Again, Everyone!

 

On the drive in this morning, I thought of a little experiment that may help to make this a bit more clear. It's worth trying!:

 

1. Open your version of Photoshop (or Elements).

 

2. Create a New file only 2 pixels on each side (4 pixels in total), and in the color black.

 

3. The Image Size window will indicate that its "Document Size" (the size at which it will print) is .028 inches at a Resolution of 72 pixels-per-inch.

 

4. Print it...you'll see a tiny black square at the center of the paper.

 

5. Back In the Image Size window, make sure that Resample is not checked, and change the Resolution to 300. The window shows that you still have a 2x2 image matrix, but its print size is now only .007 inches.

 

6. Print it, and if you look real close, you can see a microscopic dot in the center of the paper. You did not actually make it a "higher-res image" (as the original poster asked about doing)...you only printed the original pixel matrix at a much smaller size.

 

7. Back in the Image Size window, with Resample still unchecked, drop the Resolution to 2 pixels-per-inch. The window shows that you still have a 2x2 image matrix, but its "Document" (print) size is now up to 1 inch square!

 

8. Print it, and the result will depend on your printer's internal algorithms. On my two printers (laser and inkjet), it actually appears as a solid-black 1-inch square. The printers did not give me a faithful rendition of my four data pixels, but instead, interpolated and filled in data on their own...using algorithms that may not be as good as Photoshop's.

 

This exercise with a small test file demonstrates two things:

 

* That changing the Resolution without resampling simply alters the physical print size (which is perfectly OK, if that size is what you want).

 

* That changing the Resolution without resampling doesn't avoid adding or interpolating pixels in printed output...it may simply leave that task to the printer's internal algorithms, which may not be as good (image-wise) as Photoshop's "professional-grade" Bicubic resampling!

 

Sincerely,

 

Dave

[don_e]

"Hi everyone, I am a beginner at PS and need to save some images at 300 ppi. They were shot as fine JPGs on a Canon 350D. When I open them in PS Elements 5 it says they are 72 ppi images. HOwever they need to be 300 ppi for printing purposes. HOw do I do this? Many thanks!"

 

It depends on what size you want the prints. What is the pixel size of your images and what size to you want them printed?

[dave_powell2]

Hi Again Federica,

 

Just thought of another...hopefully finally better...approach to answering your question! According to dpreview.com, your 8MP camera produces a 2304x3456-pixel matrix at its highest resolution. When I create a dummy file in Photoshop with that exact number of pixels, the Image Size window tells me that (at a "Resolution" of 72) the file would print at 32x48 inches. With Resampling unchecked, entering 300 in the Resolution field changes this "Document size" to just under 8x12 inches (try this with one of your actual files).

 

So... if you actually want to output an 8x12-inch image (at 300 dpi), you're golden!

 

But if you want to print the image on smaller 8x10-inch paper, you'll need to crop and/or Resample the file down to as close as you can get to under 2400x3000 pixels (300 times 8x10). You could also let the printing device itself remove pixels, instead of your doing so through Resampling, which would probably work out OK.

 

But the REAL rub comes if you want to print the file on larger paper...say, at 12x18 inches in size. Here, you again have several options:

 

* Print the file as-is (at 300 dpi), which would leave a blank border around an 8x12-inch image on the 12x18-inch paper.

 

* Resample the file upward to as close to just under 3600x5400 pixels (300 times 12x18), and print it at 300 dpi (to pretty much fill the 12x18-inch paper).

 

* (If possible) have the printing device's operating resolution set down from 300 to 192 dpi, to lower its output resolution and again fill the 12x18-inch paper with your un-Resampled file. (Actually, this isn't as dumb as it sounds, since larger prints are usually viewed from further away...and within limits, can be printed at lower resolutions without compromizing their "apparent" quality.)

 

* Use whatever internal "upscaling" the printing device may have, to fill the paper with the un-Resampled image. This is what turned the 4-pixel test file in my last message into a 1-inch solid-black square... which demonstrated why Photoshop's resampling algorithm might give you better results than leaving this to a printing device's software.

 

By the way, the "Resolution" number that you see or enter in Photoshop's Image Size window is simply a tool to help you add or remove enough pixels to make the image print at a desired size using a desired output resolution. The Photohsop Resolution number is not actually sent to the printer with the image file! When the time comes to lay the image on paper, the printing device (or the printing lab) cares only that your file contains sufficient pixels to fill the desired print area at the desired output resolution.

 

To relate this to your camera again, its 2304x3456-pixel file will fill about 8x12 inches on your local print lab's paper (when output at 300 dpi) regardless of whether your Photoshop Image Size window says it's 32x48 inches (at 72 dpi) or 8x12 inches (at 300 dpi)!

 

Sincerely,

 

Dave

[fred_monsone]

Thanks Everyone. I'm going to print your advice and try it out!

[hashim a]

Dave... you said

 

*But if you want to print the image on smaller 8x10-inch paper, you'll need to crop and/or Resample the file down to as close as you can get to under 2400x3000 pixels (300 times 8x10). You could also let the printing device itself remove pixels, instead of your doing so through Resampling, which would probably work out OK.*

 

two questions...

 

1. any advantage to resampling downwards before getting it to the printer or is it the same as letting the printer do the resampling?

 

2. what happens when i send a file to the printer that is at something like 500 dpi when seeking a print size of 4x6... will the additional pixel density make for a *better print* than if at 300 dpi?

[dave_powell2]

Hi Hashim,

 

Good questions!

 

Q: Any advantage to resampling downwards before getting it to the printer or is it the same as letting the printer do the resampling?

 

A: Personally, I always do that (and I combine it with judicious cropping when the image's proportions differ from the desired print area's). Usually, though, letting a decent printer drop the pixels won't adversely affect the result (as long as the image proportions are OK without cropping).

 

Q: What happens when I send a file to the printer that is at something like 500 dpi when seeking a print size of 4x6... will the additional pixel density make for a *better print* than if at 300 dpi?

 

N: That depends on the printer. But in most cases, a drastically higher DPI accomplishes three things: expends more ink, lengthens the output time, and (sometimes) actually makes the ink "pool" rather unattractively on the paper! With most Epson printers, the recommended output DPI is 720 or a fraction thereof (such as 240 DPI), and many users print at 240 instead of 300, because they see almost no difference in output quality.

 

Hope that helps!

 

Sincerley,

 

Dave

[hashim a]

thanks for the quick response Dave... appreciated.

[dave_powell2]

You're most welcome, Hashim...and good luck with your tests, Fererica!

 

Sincerely,

 

Dave

[dave_powell2]

Sorry Federica, I mistyped!

 

Dave