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DPChallenge Forums >> Tips, Tricks, and Q&A >> Printing & PPI problems
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Canon EOS-40D
Canon EF-S 17-85mm f/4-5.6 IS USM
 04/24/2006 03:34:41 AM · #1
Hi all

Having problems with PPI. My printer company demands not less than 250ppi and I know to uncheck the box in Image size, but if I want to print it at A3 size (the maximum that my camera manual tells me that I can print), then my PPI stays relatively low, i.e. around 90ppi.

For example, if I size my image at 20"x24", the ppi is 154ppi. But if I cheat and size the image at 20cmx24cm, then the ppi is 330ppi. The pixel dimensions stay the same irrespestive. I then upload the image to my printer and they print it at 20"x24" (despite that it is actually sized at 20cmx24cm)

So, to the questions:

1. By doing this (changing the size to centrimetres so that the ppi is acceptable), am I effecting the quality of the image?

2. Is there a better way, am I doing something wrong that I can't get a decent ppi just by resizing with inches
Canon EOS-40D
Canon EF-S 17-85mm f/4-5.6 IS USM
 04/24/2006 09:31:50 AM · #2
bump
Canon PowerShot S3 IS
Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)
 04/24/2006 09:38:07 AM · #3
If the "pixel dimensions" remain the same, then you haven't changed anythng except the units you use to express the size. If you have 250 pixels, you can print 1 inch at 250 ppi or 2.5cm at 100 ppcm -- exactly the same.

If you want to print more than one inch from those pixels, you either have to print at a lower resolution (e.g. 2 inches at 125 ppi) or else resample the image so you create more pixels.

See if this tutorial helps.

Message edited by author 2006-04-24 09:39:47.
Canon EOS-40D
Canon EF-S 17-85mm f/4-5.6 IS USM
 04/24/2006 09:43:53 AM · #4
Originally posted by GeneralE:
If the "pixel dimensions" remain the same, then you haven't changed anythng except the units you use to express the size. If you have 250 pixels, you can print 1 inch at 250 ppi or 2.5cm at 100 ppcm -- exactly the same.

If you want to print more than one inch from those pixels, you either have to print at a lower resolution (e.g. 2 inches at 125 ppi) or else resample the image so you create more pixels.

See if this tutorial helps.


Thanks, Paul. I'll run through this tutorial and post any further queries. Might be a bit too much maths for me at 11:45pm, so I'll be trawling through that tomorrow. Thanks, again. N
Canon PowerShot S3 IS
Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)
 04/24/2006 09:56:14 AM · #5
Too much math for 6:30 a.m. (where I am) too, that's why I gave you such lame examples : )
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