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how to increase dpi while maintaining image size? -- question
Old 05-01-2003, 05:06 AM   #1 (permalink)
val
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Question: how to increase dpi while keeping size and image quality the same.

I have a jpeg sized approx as follows: 1930X3000 pixels, 10X15 inches, at 193 dpi. A magazine is interested in publishing the image (based on a smaller jpeg) but told me to send 200 dpi minimum; another source tells me mags generally print at 300dpi.

I saved the file to Tiff, now I want to up the resolution to 200 dpi and possibly 300dpi if possible -- can I do this and maintain the 10X15 size in inches and not mess up the image? Is 300dpi magazine standard? Any suggestions on preparing and submitting digital images for publication? Thanks,

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Old 05-01-2003, 05:38 AM   #2 (permalink)
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I assume you are using photoshop...just go to Image then Image Size and note the image dimensions, change the resolution to 200 or 300 then change the width and height back to what they were....I do it ALL the time.
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Re: how to increase dpi while maintaining image si
Old 05-01-2003, 10:35 AM   #3 (permalink)
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Richard is right. Go to "Image", then "Image size" and make the changes. Make sure both 'Constrain Proportions' and Resample Image' are checked and select 'Bicubic'. Going from tiff to jpg, you'll still maintain excellent quality, esp when doing your "save as", you select maximum for no reduction.

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Re: how to increase dpi while maintaining image si
Old 05-01-2003, 11:59 AM   #4 (permalink)
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I have been lurking on the board for a while and thought I should finally jump on in this subject. As a background I publish a small niche magazine and have been doing it electronically since 1986.

As a rule of thumb the dpi of an electronic image should be twice the line screen of the printed piece, such as a magazine. Thus, if the line screen of the printing plates is 150 the dpi of the photo should be 300. If the magazine is printed at a line screen of 133 then the dpi would be 200.

Now to the question of can you change the 193 dpi to something else and what effect will that have.

Yes, you can change the dpi by selecting the image size and changing the dpi at the bottom. Going from 193 to 200 will make little difference in the quality. Photoshop will make a good guess as to how to handle the extra information.

Going to 300 dpi and keeping the photo size at 10 by 15 inches may not yield a desired result. You are now asking Photoshop to add lots of extra information, i.e. pixels. It has to do some interpolations. The more interpolation the greater the chance of pixelation, loss of detail, etc.

It might look okay on the computer screen when the picture is viewed at less than 100 percent, but may not be. Scale up to 100 percent and scroll around the image to see what might have changed in quality.

If the magazine requested 200 dpi they are probably printing at 133 line screen. That doesn't mean you can't give them a 300 dpi file. If they are not going to use the photo at 10 by 15 then it is easier to up the dpi and downsize the image to maintain quality.

A 10 by 15 inch image at 193 dpi is 16mb file. At 200 dpi it is 17.2mb, shouldn't be a problem with quality. At 300 dpi it is 38.7mb, scaling this far up is asking for trouble. Increasing the dpi to 300 and resampling the size down to 7 by 10.5 will yield a 19mb file. You want to keep the new file size reasonably close to the original file size to maintain quality.

There is just so far that you can push pixels around.
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Re: how to increase dpi while maintaining image si
Old 05-01-2003, 01:18 PM   #5 (permalink)
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I must be brain dead. Maybe from staying up to 2 a.m. editing some glamour shots I took this week. Obviously, by the rule of thumb, a 133 line screen would require a 266 dpi photo. Sorry about that. However, the rest of my missive is correct. Be careful in trying to push the file size of an image.

I'm not sure why the magazine would want the image at 200 dpi, but I'm sure they have their reasons.
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Re: how to increase dpi while maintaining image size? -- question
Old 05-01-2003, 01:24 PM   #6 (permalink)
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Hi, Hugh from San Antonio...listen to these guys, they are right. But said another way, you really have to find out what the publication size of your image is. I'm guessing it's not 10x15. Your image as it stands downsized to 6.43x9.65 is 300ppi/dpi. without having to add a bunch of extra pixels. We ussually shoot for maximum image size in digital, but that doesn't mean a publisher is going to use it...My standard print size is 16x20, but magazine covers are at best 8.5x11 which would yield a very high resolution from a 16x20 image. Best thing to do is find out what they want and deliver an end product so the "crew" won't be tinkering with your image. Also, if they want a cmyk and you can do the conversion yourself, try to findout what the printer profile is...of course none of this is necessary if your talking a big league mag or publication...if your doing local stuff though, you would be amazed at how many different ways a publisher can screw up your image...Later, Hugh
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Re: how to increase dpi while maintaining image size? -- question
Old 05-01-2003, 01:37 PM   #7 (permalink)
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Just remember one thing for sure and for certain. Decreasing print size will either maintain or increase resolution and happily, print quality. Increasing print size will result in a decrease in resolution unless it is also resampled to the higher resolution and there will always be some loss of print quality no matter what you do. Hugh
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thanks everyone
Old 05-01-2003, 02:20 PM   #8 (permalink)
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for the advice. I'll up it to 200dpi (using PS 6.0) keeping resample and constrain checked. I also did auto contrast and unsharp mask and a minor crop, hopefully they don't need to do much else. aloha,

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Re: how to increase dpi while maintaining image size? -- question
Old 05-02-2003, 11:53 AM   #9 (permalink)
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The simple answer is no. If your resolution is only X dpi at 10x15", you cannot increase to 2X dpi at 10x15" without your file size increasing, not to mention your image quality dropping off as Photoshop has to interpolate pixels to make up pixels out of thin air, basically. Essentially, all files are really just X pixels x Y pixels, and the resolution size merely determines how many inches across are all these pixels going to be displayed for a final physical size.

Now there is a software product called Genuine Fractals that is able to defy gravity to a certain point and cheat this a little, but the fact is that if you have a client for your images, you had best rescan them at higher resolution and prepare for larger files, storage-wise. If you shot them digitally, well, it's Genuine Fractals, or ask Photoshop to interpolate and wince away at the results, or simply forget it. Sorry.
 
 
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