View Full Version : question: changing image from 72dpi to 300 in PS5.5
02-20-2004, 05:21 AM
I would like to know of any tips, techniques or references for processing an image from 72dpi to 300 in PS5.5 for printing.
02-20-2004, 06:14 AM
Hi Jean. How are you planning to print? If you are planning to take a digital file to a printer, the dpi does not matter in the least, they will automatically scale the photo down. If you are printing at home, and want to print to and exact size, it may or may not matter. For example, if your printer is set up to print borderless at 4x6, when you go to print, you can simply check the box which says scale to fit media. Your computer/printer will handle everything from there. If you want to be able to specify the size of print at 300dpi, it will become easier anyways to actually change the pixel density of the shot. To do this, go to Image->Image Size, then make sure that you have unchecked where it says resample image. Once you have unchecked the option, you can go to where it says resolution and change that to 300dpi, the linear (cm or inches) dimensions of the photo will change, but the total number of pixels will not, so you are not losing any information.
I am using PS 7 now, but if I remember correctly, PS5.5 was the same. I hope this makes sense and hope it helps. I am sorry if this is not applicable in PS5.5.
If there is a better way (I can also think of a much more cumbersome way), I too would be interested in knowing it.
02-20-2004, 07:10 AM
Thanks Darren, the resample part was my missing info.
02-20-2004, 05:27 PM
Upscaling is only usually viable for an increase of about 20%. It's highly unlikely that you'll be able to go from 72dpi to 300dpi. With my shots I can just about go from 240dpi to around 300 for larger prints.
02-20-2004, 06:06 PM
Ron, I don't believe we are talking about upscaling here, are we? I mean, my intention and description does not involve changing the file size, or the number of pixels, only the PPI resolution. If a shot is 3000x2000 at 300dpi, the stated print size would be 10x6.67". With 72dpi, it would be 42 inches by about 28 inches, but there would be no more and no fewer actual pixels being represented. Isn't upscaling more akin to taking a 3000x2000 pixel file and turning it into a 3600x2400 pixel file? My understanding is actually changing the resolution will have no effect on quality of print, just that it will make for easier math, especially when you are doing the printing yourself. Hope I am makings sense, although I am not sure I am.
02-21-2004, 05:14 AM
Okay now that I'm just a little confused but will survive.;-) Why would someone make this suggestion for printing. Work on a image in 72dpi up to it's desired dimensions. Create a new file with the same dimensions but change to 300dpi. Then duplicate the 72dpi image and drop into the new file. Then Print? What would this be called in Photoshop language.
02-21-2004, 08:35 AM
I raised this because I'm used to upscaling for printing purposes. My printer recommends 200-300 ppi, and provides a technique for gradually upscaling a shot to reach this level. I'm not an expert at this, but my basic understanding is that a higher ppi will afford a larger print. But then again, that assumes some 'stretching' I guess.
If we're lucky maybe someone more knowledgeable can chime in on this topic...
02-21-2004, 04:45 PM
I'm 99% certain Darren is right. Of course there's always that pesky 1% ;-)
02-22-2004, 10:08 AM
Just this morning I had more or less the same question in the dpreview.com forums and already got an answer:
> I was advised from the kodak forum to ask here again, as I was told
> in the kodak forum to just resample to 300 dpi with Photoshop.
> I always thought that if you have a 72 dpi picture and resample it
> to 300dpi you will have loss in quality.
You don't want to "resample". You want to make sure the resample option is checked off. Then change the DPI to 300. It will change the dimensions of the print (depending on what you started with). It will be smaller. For example, my pics from my camera start out at about 23 X 34 on a 5 mp pic at 72dpi. When I change the DPI for printing to 300, it changes it to about 8 X 11. Depending on how big you want to print, you can adjust the DPI as low as 200 and still have a pretty good quality print. Some say you can go as low as 180, but I don't like the results. I can usually go to as high as 12 X 16 without quaility loss.
You don't want to resample though. That will make it look just awful. The only time you want to resample is when you want to print something big form a very small file. It will still tend to have the "jaggies" though.
Resampling, as I understand it, will create pixels that don't exist from "guessing" based on what color the pixels around it would be. Depending on how much detail you have, it can be a disaster.
02-25-2004, 03:55 AM
Much appreciated Trekearth members.
02-25-2004, 06:45 PM
"[...]but there would be no more and no fewer actual pixels being represented"
Darren, you couldn't more wrong.
Here is why:
Size in pixels = Physical size * resolution (pixel by inch)
If change the resolution, you change the number of pixel.
I didn't made it up, it's in "<a href="http://www.trekearth.com/books/book66.htm" target="_blank">Adobe Photoshop 7.0 for Photographers</a>".
02-25-2004, 07:02 PM
I may not have worded things correctly, but what I was desribing does not change the pixel count at all. If you do the math, the size in pixels stays the same, the physical size is reduced and the resolution increases proportionately. My method does not change only the resolution, it also changes the physical size as well. If you do what I mentioned in photoshop, you will have no increase in file size whatsoever. I did try this in Photoshop before I posted to verify this.
eg. 1600x1200@72dpi = 22.22"x 16.67"
1600x1200@300dpi = 5.33"x 4"
Both examples are from a 2.1 megapixel grid.
I was not refering to upsampling, which would attempt to interprolate those 1600x1200 pixels up to a greater number. If you try what I have said in photoshop, you will not get an increase in the pixel size, only in the so called resolution. Ultimately, resolution is a tricky thing, even looking at numbers. A good quality digital, even at lower so called resolution, often will make a better large print than a scanned negative or slide at much higher resolution, because the higher resolution goes into resolving grain and noise from the film, not from the actual photo you are working with.
Good book you mention, BTW, I am making my way through it now.
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