Image Resolution

[DoctorT]

Hi!

I am using Corel PSP X-6 (64-bit).

Using a fractal image generator (Ultra Fractal 6.02), I created a PNG file 1,600 px by 1,200 px at 600 PPI. When I opened the file in PSP, the Image Information says the file is 1,600 px by 1,200 px but the resolution is 236.22 PPI.

I also opened the file using Paint from Windows 7 Pro and it shows the resolution to be 600 PPI.

You can find the file at http://www.acrylicmath.com/IMAGES/Newton%201.png

What's going on?

Thank you!

Dr. T

[xfsgpr]

Your units are not correct. You need to change it to pixels/Inch. See this picture:

[DoctorT]

Dear xfsgpr,

Thank you for your reply.

I am not talking about Image > Resize, I am talking about what Image > Image Information shows.

It should show 600 PPI but it shows 236.22 PPI whereas Paint from Windows 7 Pro shows the correct PPI.

Dr. T

[xfsgpr]

The figure you are seeing is Pixels Per cm; It is NOT PPI or Pixels Per Inch. See this picture.

If you want to change everything to Inches then it is in the Operating system configuration. I am in Europe/UK so I am using the metric system. Everything is in cm or mm.

Anyway, this is my explanation but some US residents will have their own exolanation because they are using the imperial system which we the British should also be using but it is the EU, especially France, who have messed everything up!!

[DoctorT]

Dear xfsgpr,

Thank you!

Mystery solved!

Dr. T

[Jean-Luc]

I think PNG cannot store DPI information (imperial) but only metric. All DPI informations are converted to metric which explains the result you see...
But it doesn't affect quality of image.
https://www.webdesignerdepot.com/2010/0 ... th-of-dpi/

[JoeB]

I think PNG cannot store DPI information (imperial) but only metric. All DPI informations are converted to metric which explains the result you see...
But it doesn't affect quality of image.
https://www.webdesignerdepot.com/2010/0 ... th-of-dpi/

While that article does a good job of explaining image resolution, it contains an error that should not be there. Image resolution, which can be changed to whatever you want in an image editor, is not DPI (Dots Per Inch). It is PPI (pixels per inch). And the author only writes that correctly only once, and well down in the article.

Dots Per Inch refers to how many dots or splots of ink a printer lays down, and that is a printer specification of the manufacturer and cannot be changed by any image editor. How many dots of ink are laid down is changed in the printer properties where you can set draft, medium, standard and photo modes.

Pixels Per Inch (PPI) is what you see when you look at the image information or resize dialogue in good image editors like PSP. That information tells the printer how many pixels of the image to print on each inch of paper. This will determine the actual size in inches (or cm - PPCM) of your printed image. As the article points out, it has absolutely nothing to do with the size an image will display on a monitor. You will not find any dialogue or setting in PSP or Photoshop that has an option to change DPI. Only PPI.

And yes, as far as I know PNG can only store image resolution information in metric form, hence PPCM (Pixels Per Centimeter). PSP does not have an option that will automatically convert the metric measurement to imperial.

[Jean-Luc]

Image resolution, which can be changed to whatever you want in an image editor, is not DPI (Dots Per Inch). It is PPI (pixels per inch). And the author only writes that correctly only once, and well down in the article.

You are right !

In French, we have a translation problem : PPP is Point Par Pouces (Inches) or Pixel Par Pouces. There is a confusion between Points (dots) and Pixels. Different concepts but same first letter. When someone speaks about PPP, we don't know if it is Points (dots) or Pixels. So, it is more convenient, as I do, to say DPI because Dots are implicit for me.
There is also a "pollution" made by Photoshop which includes a "physical size" information in the file. Such image displayed in PS displays its "physical" (printed) size. PaintShop Pro doesn't do that.
We're not out of the woods!

[DoctorT]

Dear Jean-Luc and JoeB,

Thank you for your replies.

I now have a better understanding of PPI and DPI.

Dr. T