Camera dpi help

[karen donnybrook]

Good evening Everyone (well it is evening in Australia!),

I have a query about my camera's dpi. I have a Canon PowerShot A75 and have found that it does not matter what I do, the images are at 180dpi - is this normal? I have it set on the L (large) S (superfine) setting; in other words the best setting available (I think).

[TonyW]

Although I don't know the camera that sounds normal - when you change the setting you change the number of pixels and the JPEG compression but it's the software that translates this into dpi. So at the large superfine setting you'll get the biggest file, largest number of pixels and the best quality but the resolution won't change. My camera always comes out at 72 dpi. I always use the largest size at the least compression to get the best quality available.

Tony

[karen donnybrook]

Tony, do you change the dpi before you start working on an image or leave it as it is? I am asking this because in some of Wendy's tutorials, she instructs us to start with a certain size "page" with 300dpi. If I start with a 300dpi page and insert a 180dpi image, I have to resize the image quite a bit.

[Wendy]

Hi Karen ...

The only reason I do tuts at 300 resolution is because if I do them at a high resolution then its easy to scale down.

Some tuts on the web use very low resolution and small sizes .. I found that after I had done all the work on them they were too low a resolution to use for anything ... so I decided that I would do mine at a high resolution which will scale down if need be. :)

When I insert images into any of them I tend to just drag the corners of the inserted image in to resize :)


Wendy

[karen donnybrook]

Thanks Wendy, that does make sense.

[TonyW]

Karen I don't usually bother to change the size of the image. You do have to be careful you don't lose pixels though which can happen if you use transform to drag the image to a new size. So if you want to work at a specific resolution it's a good idea to use resize and make sure the resample box isn't checked.

So with your camera shooting Large you'll get a 2048x1536 pixel image which at 180 dpi will be 11.4"x8.5". If you resize to 300 dpi without resampling you'll have the same number of pixels but the image will now be 6.8"x5.1". If you kept the dpi at 180 and resized to 6.8x5.1 using transform you'd be losing pixels (it would now be 1230x920).

It can be confusing ;)

Tony

[Benny Pedersen]

Hi Karen ...

The only reason I do tuts at 300 resolution is because if I do them at a high resolution then its easy to scale down.

Some tuts on the web use very low resolution and small sizes .. I found that after I had done all the work on them they were too low a resolution to use for anything ... so I decided that I would do mine at a high resolution which will scale down if need be. :)

When I insert images into any of them I tend to just drag the corners of the inserted image in to resize :)


Wendy

hmmm, I also sometimes wonder why my first camera seems shooting in 72 dpi, but then I found this one:

The Myth of DPI,
http://www.rideau-info.com/genealogy/digital/dpi.html

Benny

[Cmcburnett]

Benny, very interesting article. Thank you very much;)

[Codebreaker]

The dpi setting that digital cameras provide is nothing more than a recommendation. It comes from the fact that there is a field in the Exif information for DPI settings that is really relevant for electronic document interchange where you need to re-create the document at the original size. For this you need both Pixels Dimensions and the resolution used, say, when scanning.

With a digital camera there is no original physical size, you determine a physical size when you process the image, either for display or print purposes.

If a digital camera does not put a value in the Resolution field of the Exif data then the default is 72dpi.

The formula is Pixel Dimensions / Resolution = Physical Size.

These days the use of PPI and DPI is interchangeable although there is a real difference when it comes to printing.

Colin