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I'm totally new to photoshop and I need to do something I don't really know how.

I got a picture with 100 dpi. We want that picture to be printed on a poster. I need to increase that 100 dpi to 300 dpi.

In photoshop, I went to Image/Image size. I uncheked "Resample Image", switched 100 pixel/inches to 300, but the document size has decreased. The thing is that I do not want to change the poster size. Is the "document size" the same as the poster size? If yes, what should I do to conserve the actual size with increasing from 100dpi to 300dpi? Is growing the image size from 3x is the better solution?

Thanks.

Shadowizoo
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    Wrong place for this kind of question, you would have better luck asking it here: http://graphicdesign.stackexchange.com/ ... I will flag this answer and a moderator can move it over for you. – CenterOrbit Jul 09 '12 at 19:53
  • If you uncheck "resample" then the document size should remain consistent, because all you are doing is changing the relationship between pixels and physical dimension. If I have 100 pixels I can stretch them out to 1 inch (100 ppi) or compress them to a third of an inch (300 ppi). In both cases I still only have 100 pixels (same document size) but their coverage varies. Also note that `ppi` (pixels per inch) is favored over `dpi` (dots per inch) as the latter refers to something different in the context of professional print shops. – JYelton Jul 09 '12 at 20:21

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Photoshop, for all the power it has, is still a raster image editor at the core. DPI settings are simply a conversion factor. If you want a larger image, you'll have to increase the canvas size, or REDUCE the dpi setting

e.g.

100x100 image @ 100dpi = 1" x 1" image
100x100 image @ 200dpi  = 0.5" x 0.5"

to "increase the size" of the printed images, you need to REDUCE the dpi count, so that

100x100 image @ 5dpi = 20" x 20"
Marc B
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  • 3545x7088 image @ 100dpi = 36" x 70" 3545x7088 image @ 300dpi = 11" x 23" I do not want a larger or smaller image at final print. What I expect to do is getting a 2545x7088 image @ 300dpi with the 36" x 70". Is an other program better than photoshop for doing this? – Shadowizoo Jul 09 '12 at 20:03
  • then you'd need a (300*36) x (300*70) = 10,800 x 21,000 source image. Remember, DPI is just a **CONVERSION FACTOR**. It is not a measurement like "10 meters" is. It's more like "meters per second". – Marc B Jul 09 '12 at 20:07