One for the photo experts - dpi setting

[#1]

I have a jpg picture taken on my camera at 180 dpi and I have increased the dpi to 300 by shrinking the print size using Faststone. The file information now says it is 300dpi
However opening it in Photoshop CS2 and Photoshop says it is still 180dpi.
Any ideas

[#2]

The only thing I can think of is that one's a DPI value specified by the EXIF information and the other's a DPI value specified in the standard JPG headers - and that Faststone (which I've never even heard of, let alone have experience of) changed one but not the other. Why did you want to alter the DPI anyway? It doesn't really achieve anything - whatever you were hoping to achieve can probably be dealt with using a more robust method.

[#3]

Because I needed 300 dpi for the commercial printer
Will check your theory tomorrow - it's a bit late now

[#4]

try it with Irfanview, that can alter the size and show you the exif details and its free http://www.irfanview.com/  the exif, go to image on top line, then information, the exif button is at the bottom left.

[#5]

difference between irfanview and faststone exif info

[#6]

That shows it as 300dpi also
Removing jpeg metadata changes it to 96dpi in file properties

[#7]

using Irfanview I made sure everything was at 300dpi but still Photoshop says it is 180dpi

[#8]

What about the physical print size? Maybe Photoshop thinks the same number of pixels are to be printed on a bigger sheet of paper.

[#9]

Something is seriously adrift.
FastStone and Irfanview report it as 300dpi but Gimp reports it as 72dpi

[#10]

OK - I now understand what is happening in Gimp - it probably applies to Photoshop although I can't be bothered to check as I don't havr Photoshop installed on Windows 7
The dpi reported takes no account of the dpi in the file information but is the default new image dpi - changing this changes the reported dpi regardless of the EXIF data

[#11]

Looks to me like it is all down to the actual print size. In your last but one screenshot it says the image size is 958 x 687mm - that is a very big photograph! We have, of course, three variables - print size, actual number of pixels and DPI. You can declare any two and calculate the third. I can only suspect that different software makes different decisions about which is which.

[#12]

No print size has no effect - I changed it from A4 to A2 and it made no difference
One thing which I have found is that the EXIF data being picked up by Photoshop and the camera sets the dpi in the EXIF at 180dpi - and it isn't changeable in the camera.
It would appear that Gimp and Photoshop do it differently.
Photoshop uses the EXIF data from the camera whereas Gimp using the default dpi you have set in the program
It also appears that the camera set EXIF data isn't easily modified by some of the programs even though I thought I changed it.

[#13]

exif can be changed, I have two GPS programs that do, and not all programs retain Exif when resaving.  I have Paint Shop Pro 7 that doesnt. but IrfanView does. (goes away to google exif)

[#14]

from Wiki
http://en.wikipedia.org/wiki/Exchangeable_image_file_format#Viewing_and_editing_Exif_data  link to program http://www.opanda.com/en/iexif/download.htm

Quote

Viewing and editing Exif data In the original release of Windows XP, a subset of the Exif information may be viewed by right clicking on an image file and clicking properties; from the properties dialog click the Summary tab and then the Advanced button. However, this can damage certain Exif headers if changes are applied.[10] This was corrected in a XP service pack. In Windows Mobile(Pocket PC), freeware XnView Pocket can display the Exif data. On Mac OS X 10.4 and above, this information may be viewed in the Finder by doing Get Info on a file and expanding the More Info section. On Unix systems using the GNOME desktop environment, a subset of Exif data can be seen by right clicking the file in the Nautilus file manager and selecting properties. In KDE, it can be seen by right clicking, selecting "Properties" and then "Meta info". Most Unix image viewers give the full set of Exif data. There are many software tools available which allow both viewing and editing of Exif data. The Opanda IExif Viewer is a free stand-alone application for viewing Exif data and also a plug-in for Internet Explorer and Firefox on Windows platforms. It allows examination of detailed Exif data online by right clicking on an image.[11] FxIF and Exif Viewer are multi-platform extensions for Firefox that display Exif data in the image properties dialog. This feature is native in the web browser Opera, under image properties. Retrieval of detailed Exif data not usually displayed by other programs can be accomplished using ExifTool which runs in Perl, and is available for all platforms. For AmigaOS/MorphOS SView5 as well as .NET covers a lot of the previously mentioned functionality. To deal with the privacy problems that Exif may pose to those who share their photographs with others, specialized metadata removal tools which can remove Exif exist.[12]