Pentax users hate photoshop

Interesting. We do have some competition software that will only accept 72ppi images, but I guess that's a different issue.

Eh? Do you mean on this forum? I don't that's true either, sorry

No, I don't mean on this forum. It's a separate program for camera club competitions.

Without getting distracted by that, if the screen resolution doesn't matter then why does Photoshop have a default value for documents for screen viewing of 72ppi?

Surely if we display our documents at the native resolution of devices it means that the video card doesn't need to interpolate and we should therefore in theory get the best possible result?

John, hasn't the PPI not so much to do with actual pixels but more with the size of something.

Like if you say you want a A4 canvas, there is a zoom options in photoshop that use the 72ppi to make the paper precisely the size of an A4 paper on your monitor.
Atleast if your monitor is 72ppi.

I don't think the actual PPI settings distort the pixel ratio so to say, 100% zoom is still 1:1 pixel on every monitor.

Am I on the right track here or do I wander beside it

yes, they do, which is why GIMP has a "dot for dot" setting. You'll then get your pic at the right dpi for your monitor.

Bret

Well, I think the detractors I intended to refer to are those who do not understand the useage of the software, rather than those who choose not to use it.

If it is just a matter of 'getting it right in camera' then I would still say that a digital image taken as a RAW file will need work done on it to extract the best image. A jpeg file will have had some of that work done 'in camera' and probably more crudely that could have been done in PS.

I also disagree with another poster, who said that PS was good for improving a bad image. A bad image is just that and you cannot make a silk purse from a sow's ear. PS is there to enhance the basic file to produce the finest image possible.

Manipulation on the other hand is something entirely different. Moving pixels around or cloning to remove blemishes or unwanted objects is 'artistic licence' and produces something other than a straight pgotograph. I see no problem with this if one is trying to produce an artistic rendition of what one saw through the viewfinder.

How many Brides would be happy to have wedding photos, where the wedding dress was grey and every skin blemish was rendered 'as is' in close ups? Not that many I would suggest.

Where it goes wrong IMHO is in reportage photos, where things are changed intentionally to decieve, or in competitions, where manipulation has been ruled out, such as for Natural History subjects.

As you say, each to his own. Both are valid if the photographer is happy with his work. Other's opinions are just that.

Probably because it has to default to something, first professional users tended to favour Macs and Macs then used 72ppi.

But they don't interpolate in this case. A picture that is 600x600 in PS will show as 600x600 on any monitor.

Stefan is right.

The PPI number doesn't change the resolution and is just a setting stored in the Exif info.

It is only used by programs or devices in special cases when you want to control the actual size of the displayed or printed image.

It is not used by software or your monitor when displaying images normally. The image browser resizes in its own way if any resizing is needed, and the monitor simply takes one pixel it's given and puts it into one pixel of its screen, and so on.

Thank you Pete for the explanation

My understanding is that the video card doesn't interpolate at all when normally displaying computer images. It doesn't need to.

PPI stands for pixels per inch. This is normally ignored and the monitor puts however many pixels there are in one inch of its screen. So you automatically get the best possible result regardless of the PPI setting.

An 800x600 image, for example, will normally vary in actual size according to the size of the monitor's pixels, but it will always be 800x600 pixels unless your image browsing program has resized it.

My pleasure, but I'm not an expert on this. I stand to be corrected. I'm pretty sure I'm right, though. I just might not have explained it with the correct technical terms.

In photoshop elements I have altered the screen resolution to 90pixels/inch (Edit > Preferences > Units and Rulers) so that when I'm working on a document and view at 'print size', it will actually be shown at its actual size (an A4 image, whatever the image ppi setting, will appear A4 sized on screen). I find this useful to make sure I haven't used a font that appears too small in printed form, for instance.

You can work out the screen resolution by dividing 25.4 (mm in an inch) by the pixel pitch of your monitor, which you'll find in the specifications. My HP2275w has a pixel pitch of 0.282mm, so 25.4/0.282 = 90

Exactly.

Dan

So that the image is displayed in the monitor's native resolution (assuming it is 72 ppi) in case you select a special option in your program to display in actual size. "Actual size" in this sense doesn't mean 1:1, but the size specified in the Exif.

Normally you don't use such an option, so the setting is ignored and the image is automatically displayed in the native resoltion anyway.

Just to add a little more to what has been a very interesting thread ...
Photoshop 6 - the PPI can only be changed between:
72-PPI (defined as Postscript)
72.27 PPI (defined as Traditional)
unless one leaves it until after the image has been loaded.
So our 3872x2592 image (K200D) is roughly 53x36 inches.
I want a 10x8 print so I re-size the image - this leads to all sorts of aliasing problems - and my printer will do a lot better than 72PPI.
So, I resample first, and then resize - my 10x8 is still at 380PPI, and the print quality is much better.
That's Photoshop 6, Serif Photoplus X2 has a default of 96 pix/in, and this can be adjusted. This is of course close to Dan's setting and Serif started to make a name with DTP software, so one can see why they might have chosen it.
PSE4 on the Mac starts at 72 but if the 3872x2592 image is resized to 10x8 the resolution changes to 380PPI - without me having to do anything. And, better yet, the printout is of a very high quality, with the aliasing almost minimal.
If only I had time to do all the experiments
Geoff

Geoff, I think you give PPI to much credit. It's just a measurement of how many pixels there are in an inch.
It's only interesting to play with that if you want 1:1 print proof.

Also printers don't use PPI that's for monitor and other pixel devices, printers use DPI, and that's something else.
Altering your PPI will not have an effect on your pixel size or print size.