There’s a fixed relationship between those three values: resolution (dots/inch) * physical size (inches) = pixel count (dots). If you change the resolution, you’re either changing the physical size, which would mean that 1" x 1" image isn’t going to be 1 square inch anymore, or you’re resampling.
Yes, the physical size is changing. We’re not the ones who said anything about keeping it constant.
Which is what the OP appears to have wanted.
The OP wants to keep the image at the same dimension, but increase the number of pixels so it prints better
But it won’t, whether you resample or not, because you’ve only got the original number of pixels to work with.
Try this, gang:
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Scan a photo that’s 3 inches square at 300 ppi.
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Keep it 3 inches, but change the resolution to 1 ppi. (yes, 1 ppi.)
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Now, still keeping it 3 inches, change the resolution to 240 ppi. Resample to your heart’s content.
Is the image after step three going to print better than the image after step two?
Is either going to be anything like the original 300ppi scan?
[QUOTE=VernWinterbottom]
The OP wants to keep the image at the same dimension, but increase the number of pixels so it prints better/QUOTE]
Huh? That’s resampling. My initial answer was to prevent resampling, and I got a positive response from the OP. Yes, I know DPI, PPI, and related commonly-misused terms can be confusing. But given that I worked out what the OP wanted, and provided the solution immediately, I wish people would stop telling me that I’ve misunderstood summat-or-other.
[QUOTE=GorillaMan]
I got your back here. I don’t know why everyone is confusing the issue here, either. You’re right. The OP just wants the exact same picture at 240 ppi instead of 72 ppi, because that was his teacher’s specs. That’s exactly what you showed him how to do.
That’s entirely true. (Not relevant to the OP at all, but since it was answered right away I don’t mind continuing the hijack.)
I made an action that is specifically intended to to increase the resolution of images that are sampled at a low resolution (or scanned from PMT/halftone images) to make them look better as large format prints. It separates the image into CMYK and reaverages the colours so you don’t have sharply-defined dots and jaggies and then recombines them, sharpens it up, and corrects the levels.
Of course it’s not the same as actually recovering information that’s not there, but in some instances the end result is practically the same. (It’s really only practical for illustrations – especially coloured line-art.)
In my opinion, the OP wanted to increase resolution from 72 to 240 while keeping the image at the same dimension in order to make it print better.
The teacher said that couldn’t be done: basically changing the resolution while keeping the image the same dimension would NOT make it print better.
OP then says the teacher’s judgement is questionable.
Gorillaman then said to uncheck “resample image.”
But unchecking “resample image” makes the dimensions of the image shrink in dimension, so that doesn’t do what the OP wants to do. (I just did this. I had a 4.222 inch by 5.681 inch image at 72 ppi. I unchecked resample and increased the resolution to 240 ppi. Photoshop gave me a 1.267 inch by 1.704 inch photo at 240 ppi. When resample is unchecked, Photoshop will not let the dimensions of the image stay the same.)
But what I’m saying is, if the OP takes a 72 ppi image and wants to change it to 240 ppi, while keeping it the same dimension, resample must stay checked. However that same dimension image, now at 240 dpi, WILL NOT PRINT ANY BETTER.
The teacher is, in fact, correct that the OP cannot change a 72 ppi image into a 240 ppi image and keep it the same dimension and make it print better. Once an image has been saved at 72 ppi, it’s tough to get a good print from it no matter what you do.
The OP said nothing about making it print better, just at a higher resolution.
The pixel dimensions remain the same. Suppose it’s an 8X10 scanned in at 600ppi, arbitrarily. The pixel dimensions are 4800X6000. If you print it out from the .psd, you’ve got – naturally, an 8" X 10" print.
But then for some reason you save it as a .gif or some such, which automatically changes the ppi to 72. The pixel dimensions haven’t changed, but now the print dimensions are 67" X 83". The resolution has changed, and the print dimension has changed. The image wasn’t resampled when it was saved as a .gif.
If you want to correct this, you uncheck “resample image” and change the ppi in “image size.” The pixel dimensions never change. They never have changed. This is why the OP is happy with something that apparently shrinks the print dimension – because it’s correcting the increase of the print dimension that resulted from the file being saved at 72ppi.
The OP wants to prevent the pixel dimension from changing. The print dimension changed when the .ppi was changed to 72 when it was saved as a compressed file.
This was really sorted out in post #2.
whatever. . .
I get where you’re coming from, it’s just that you missed that when the resolution was first lowered, the image wasn’t resampled, so no image data was lost.
The net result is that the document size (print dimension) increased somewhat in the change from 600ppi to 240ppi. So long as the original image was small enough that it will still fit on the page at that resolution then the problem is totally fixed.
Otherwise, he can change the document size (with “resample image” checked) to make it fit on the page (which will keep the instructor’s specified resolution and simply discard the “extra” pixels.) Either way, everything’s cool.
If you’re not used to working to print, it’s easy to get confused by this.
Larry,
I’ve been involved with and employed in the printing/publishing industry since around the dawn of paste-up. I actually used to hand set type out of a California job case when I first started. I’ve used real live leading between lines of type. I’ve been using PageMaker since about 1985 and PhotoShop since maybe 1990.
My wife and I now publish a monthly magazine full of halftone photos and line art. I design and lay out the entire publication, including 95% of the advertisements, using client materials including photographs, tiffs, jpegs, and pdfs. We now use a digital camera, as do our contributing journalists and photographers.
I know all about getting a jpeg that’s twenty-something inches wide at 72 ppi and reducing it to a 4.85-inch wide tiff at 225 ppi, which the printing plant uses. (We’re basically a B&W plus spot color publication, web printed on good quality newsprint.)
I know the local real estate agent cannot comprehend any instruction more complicated than, “Just send me your photos as big as you possibly can.”
Nothing that I’ve ever had printed has been less than 100% professional.
I truly think the OP, obviously a student, was not completely clear about precisely what the teacher was requesting and why the teacher’s judgement was untrustworthy.
We’re all making different assumptions about the OP and our arguing amongst ourselves is pointless.
I meant without changing the pixel dimensions. How the hell did this turn into a debate?
Oh, and I don’t trust my teacher’s judgement because he doesn’t know how tolerance works (“If you have a tolerance of 1 it will select 1 pixel away from where you click”), doesn’t seem to fully understand anything technical, can’t use half the tools he demonstrates to us and is a militant Mac user, which isn’t significant on its own but paired with other things makes you wonder a little.