What resolution should I use for my photos in Inkscape?

question from a non-graphic designer here who doesn't fully get the whole 'resolution' thing.

From what I understand, Inkscape saves all embedded images as 90dpi. However for printing, 300 dpi is typically recommended.

If I add a 300dpi image to an Inkscape document, it will appear much bigger than its correct size as it scales down to 90dpi. Does this mean that I am OK to save at 90dpi, because I am shrinking the size of the image?

What about if I have a low resolution photo, say 72dpi, but the photo is large and I am happy to shrink it? Should I first change the image to 90dpi in Photoshop before embedding it in Inkscape, or can I just add it to Inkscape and resize it?

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2 Answers

'What should be the resolution" depends on various things.But most import thing is "Distance form where it will be viewd". 300dpi is typical thing for prints.But not for all types of print.Business card, magazine, posters which are used to view form close distance, require higher dpi(240-300 dpi) for avoid pixelation.But when printing huge billboard which will be viewed form a great distance generally print as low as 12-15 dpi, but we don't see any pixelation, and it appears sharp.So its really depends upon in where your art work will be displayed or to be viewd from.Resolution is not the main thing, import thing is how many pixels do you have in the image natively.

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why negative vote? – user1187405 Sep 20 '13 at 21:07

A `100px by 100px` image at `90dpi` needs to be `333px by 333px` to be considered `300dpi`

An easy way to do the math is to take your target dpi (300) and divide it by your current dpi (90) and the multiply the pixel width and height by that factor.

So in the above example `300/90 = 3.3333333`, so then you take the width and height (in this case both are 100) and do `100*3.33333 = 333`

Basically, when you're increasing the `dpi`, you're increasing the actually height and width of the image in pixels (as printing an image smaller than it actually is makes the quality seem higher)

Changing the dpi in Photoshop before bringing it into Inkscape will only change the size of the image.

For instance, if you have a photo at 72 dpi that is 100 x 100 pixels and want to print it at 300 dpi, you would divide `72/300 = .24` and then you'd multiply `100*0.24`, which would leave you with a `24px by 24px` image when it's printed.

EDIT

If you want to figure how big an image will be when printed (at a certain dpi) you would take the number of pixels and divide them by the dpi.

So an image that is `300px by 300px` at `300dpi` would end up being `1" by 1"` and an image `300px by 300px` at `150dpi` would be `2" by 2"`.

So if you know you want to print a `4" by 6"` postcard at `300dpi` you would want a document that is `1200px by 1800px` (`4*300 = 1200` and `6*300 = 1800`)

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The equations need a physical print size (with dpi, typically 'inch'). So, it's better to use an example of a 1" x 1" image rather than 100px x 100px. – DA01 Sep 19 '13 at 17:59
I made an edit on how to relate actual pixels and dpi to what you get on paper. – Johannes Sep 19 '13 at 19:05
OK, so if I scale the width and height of image down inside an Inkscape document, does the resolution increase, or does it resample the image and decrease the resolution? I'm just wanting to know what the most effective way is of maintaining image quality when the images start of as low dpi (e.g. 72dpi). – cbp Sep 19 '13 at 23:11
Honestly, I don't know Inkscape. But I would imagine that if you're simply scaling an image down inside of the software that you would be resampling. But there may be a way to resize instead of resample, much like you can do in Photoshop. And if you have Photoshop (which is sounds like you do) you could just use that. – Johannes Sep 20 '13 at 1:01
Could whomever downvoted explain why? A downvote without an explanation doesn't really help anyone. – Johannes Sep 20 '13 at 1:36