Changing DPI up/down OK ?

[KIPAX]

Does changing thye DPI in photoshop upwards ahve any effect on the file.

If I have a file with 200 DPI .. then decide I want 300 DPI .. I am guessing this is no problem and has no effect on the file.. its just the info to the printer... I am guessing thats correct but am looking for factual confirmation

 

[Grendel]

By increasing the ppi you won't actually increase the resolution per se. Photoshop will interpolate the image, which means it will invent pixels based on the info of neibouring pixels to "fill the gaps". By taking an image from 200 ppi to 300 ppi photoshop has to somehow put 100 more pixels in every inch of image.

The outcome is that you will end up with a 300 ppi image but it will loose a fair degree of sharpness and it will look a bit "fuzzy". The greater the increase in ppi the more pronounced this degratation will be.

HTH

 

[KIPAX]

Cheers Grendel and thats just on printing and now on screen yes..ie on web.. So best to save at highest DPI?

 

[Grendel]

Absolutely. IMO it's always best to save at 300 ppi from the outset as that is the ideal resolution for printing. You can always scale down without any loss of quality but you can't scale up without some degree of quality loss.

There is a theory that if you upsize in 10% increments Photoshop does a far better job of the interpolation that if you make one big jump in size. I've never put it to the test to see if there really is a noticable difference though

 

[Paul-S]

Does changing thye DPI in photoshop upwards ahve any effect on the file.

If I have a file with 200 DPI .. then decide I want 300 DPI .. I am guessing this is no problem and has no effect on the file.. its just the info to the printer... I am guessing thats correct but am looking for factual confirmation

It depends..if when you resize you have the the resample box unticked then no.
If it is ticked then yes it will change the file.

 

[Craikeybaby]

For on screen viewing changing the PPI will make no difference, to the file, also the image will look the same on screen as the pixel size is set.

For printing, one of two things will happen, depending on you settings. If you don't resample the image, the physical size of the image will change, it will be smaller if you increase the dpi and bigger if you reduce the dpi. If you choose to keep the image size the same pixels will either be lost or created.

FWIW Lightroom does a much better job of interpolating images than PS, they use a different algorithm.

 

[MJ Stebbings]

FWIW Lightroom does a much better job of interpolating images than PS, they use a different algorithm.

I was just looking for something similar about this.

If i convert a 8.2mp image (from my 30d) at 300dpi, it produces and image of around 11.5x7.5in.
I like to process my images at 12x8in as thats usually the biggest print size i will make from them.

Would it be best to convert them from Raw to JPEG using lightroom, and doing them at 12x8in 300dpi?

 

[Craikeybaby]

My advice would be to do the processing, then resize for export...

 

[Jayst84]

Does changing thye DPI in photoshop upwards ahve any effect on the file.

If I have a file with 200 DPI .. then decide I want 300 DPI .. I am guessing this is no problem and has no effect on the file.. its just the info to the printer... I am guessing thats correct but am looking for factual confirmation

Correct. Changing DPI or PPI whatever you want to call it. Has no effect on the file on you computer. Only changing the spatial resolution does, ie the number of pixels. The DPI is just for output.