DPI help

[Cutter]

Originally Posted by Stormsong

Yes, that certainly sounds big enough in terms of what you want! I hope it all works out okay for you.

Regards,
Denise

Thanks Denise you have been a great help, if ever you need your hair doing Call in

[cosmicma]

youv'e got to keep in mind there is only 2 ways of making a larger image ( apart from re scanning an image )
one is to pixel stretch ( not recomended ) and the other is to pixel double ( a better method )

there is various dedicated software for pixel doubling that do it inteligently photoshop does a pretty good job

here's a page that will give you more info on the subject
http://graphicssoft.about.com/od/inc...n_Software.htm

[neil_ross]

i understand this is an old thread but couldnt you just change the preset settings to 300dpi when exporting to jepg from a RAW?

[cosmicma]

i was having a converstaion about this very subject last night

the converstaion was about some art work somebody had done and wanted it to be blown up to A0 which is quite a big print at the end of the day
the original art work is hand drawn but the image they wanted blown up was an A4 print of the original my advice was to forget it unless he could get hold of the original artwork and scan that at the maximum optical resolution of the scanner used and then the dpi issue came into question as to why he couldn't do that with a print

so back to the OP's original query
yes you could state the desired DPI from raw but if the original image is 250 DPI by default raising it to 300dpi would give you a bigger file but thats about it and in reality would soften the image because those extra dpi would have to be made up there is no more information to make up for those extra pixels

so mark wants an image printing at 48 x 24 inch ( which is probably done by now ) and if my thoughts are correct the chances are the image originated from a canon 50d which has a natural resolution of 4752 x 3168 pixels which equates to 102 DPI ( as allready stated ) at the desired print size
to print at 300 DPI the image woud need to be resized just stretching the image to print at the desired size would produce a soft image and this is where clever interpolation comes into effect by inteligently looking at adjacent pixels and adding accordingly
the end result is an image that is bigger and hopefully just a sharp as the original to the naked eye

the viewing distance needs to be taken into consideration too
an A4 print would obviously be viewed a lot closer than a 4 x 2 foot large print and because of this the 300 DPI goal becomes less important it would probably be very acceptable printed at 102 DPI but close scrutiny would show the print to be a little soft
but what has to be understood is even by achieving the 300dpi goal at 48 x 24 inch there is no more information to make up those extra pixels it's tom foolary to make you think there is with an end result the image stays sharp under close examination

there's a very easy way to check how well the interpolation method of choice is doing
resize your image, and print a detailed part of the image that would fit on an A4 page
compare this to the same detailed part of the original sized image both printed at 300dpi