question about dpi, image size and printability

Perseus

Perseus

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Lets say I have a small creation in Photoshop of about 2000 x 2000 pixels (about 7 inches square) at 300 dpi, could I print this baby out 3 times the size and still retain highest quality and clarity? I know that resizing the image itself would lessen image quality but what about printing?
 
Well... That's easy, really. If you blow the graphic up to three times its size, you'll lose resolution (it'll be about 100 dpi). So no: You definitely _won't_ keep highest quality and clarity. Why would it be different for printing than on screen?
 
There are ways around this, however.

1. Resize your image a few times to get up to your desired size. I've found the interpolation works better in steps than all at once.

2. When printing large format, 150dpi is usually plenty (notice how big transluscent bus signage/ads have a bit of noise in them? this is to cover lower resolution issues). Use noise especially if you have any blended colors or gradients.

3. If you have any text in your file I recommend removing it and using Illustrator or a page layout program like InDesign or Quark to add your text: It will be more crisp and clear this way since fonts can rip cleanly at any size; raster can't.
 
The advice above is probably the best advice you can get on the issue. But there is something that nobody can overlook here; that is usage.

If you're going to blow up a huge event sized poster that will hang above a gallery then dpi won't play too big of a part (it's going to look choppy up close regardless). Then again, if you're going to print out a design to put on your car, something people will see up-close constantly, dpi shouldn't be taken too lightly.
 
I've heard from some of my pro photographer clients and also read in a book about Photoshop for Digital Photography that you can blow the image up incrementally by sizing up 110% repeatedly until you reach your desired size. They claim that it won't loose any quality.

My suggestion is to create an action in Photoshop for sizing up by 110% and set a key (like COMMAND + F1) to run that action.
 
macworks said:
I've heard from some of my pro photographer clients and also read in a book about Photoshop for Digital Photography that you can blow the image up incrementally by sizing up 110% repeatedly until you reach your desired size. They claim that it won't loose any quality.

My suggestion is to create an action in Photoshop for sizing up by 110% and set a key (like COMMAND + F1) to run that action.
Click to expand...

Well, that's not exactly true. Simply taking a photo causes the image to lose resolution because it is a digital translation of light. Further, as you incrementally increase the image size (resampling) the computer uses an algorithm to interpolate pixels; basically filling in the blanks that aren't really there. This causes quality loss and is pretty widely known.

Remember audio tapes? When you recorded a recording you doubled your hiss. It's the same with an image. You not only increase the image but also the imperfections the more you resample.

Read more on the subject here (and direct your photography friends to this as well): http://photography.about.com/library/weekly/aa081301a.htm

and this quote in particular, "Make sure you understand the difference in Photoshop between altering the resolution (which leaves the file size unchanged, but alters the output dimensions) and resampling. Resampling adds or takes away pixels from the file, changing the actual number of pixels. In general, normal image manipulation software can do a good job of making images smaller, but is poor when used to increase image size. It simply bulks the file out without increasing detail.

Unless you have fractal or other special interpolation software, the printer driver will probably make as good a job of increasing your image size as the interpolation algorithms built in to standard imaging software such as Photoshop, so there is seldom any point in increasing file sizes in Photoshop."
 
150dpi is just about the minimum resolution you can realistically print from, and keep a reasonable level of quality. 300dpi is the optimum. an image created to be 300dpi will look really good printed, everything should be crisp. the downside of this is that it becomesvery processor intensive the more inches you add.
 
If your image is at 300 DPI, lowering the DPI to 240 would result in an increase in printable size without a noticeable loss in quality. I generally print my photos at 240 DPI and can't tell the difference between that and 300 DPI. I've been told by photographers that the human eye can't really tell the difference above 240 DPI.
 
Print usually occurs at 150 lines per inch, not dpi which is a screen resolution. Newsprint is about 100lpi, magazines usually 125 or so.

I think that lowering the dpi and raising the dimensions proportionally doesn't actually do anything to the image if those changes cancel each other out...
 
2 X the linescreen is the best rule, you can go to 1.8 X linescreen if you need to and get good results. It's sampling theory you're dealing with here. 300 DPI is OK and usually considered a standard but it's actually a bit high if you're running a 133 LPI screen which is very common.

Lots of newbies think the higher the resolution the better but that's not the case. An image which has too high a resolution actually results in a a muddier image, less contrasty. Sometimes that's what you want but usually not.

If you do a lot of printing you can verify this for yourself, try some low resolution images, maybe 120 dpi and you'll see how bright they look but at the expense of detail. Then try the opposite.

I used to own a print shop so I've had lots of practice and made plenty of mistakes.
 
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