Change of DPI (Set DPI vs. Resize)

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Change of DPI (Set DPI vs. Resize)

Postby Troken » Mon Nov 27, 2006 7:50 am

Wouldn't it be better to combine the "Set DPI"-function and "Resize"? I don't really get it why there is no simple way of changing the DPI in the "resize" dialog. I just recently found the "set DPI" and that feels strange that these functions are separated.
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Re: Change of DPI (Set DPI vs. Resize)

Postby xnview » Mon Nov 27, 2006 8:02 am

Troken wrote:Wouldn't it be better to combine the "Set DPI"-function and "Resize"? I don't really get it why there is no simple way of changing the DPI in the "resize" dialog. I just recently found the "set DPI" and that feels strange that these functions are separated.

Set DPI is only to change the value of this field...
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Postby Troken » Mon Nov 27, 2006 10:05 am

Yes, but if you change the DPI of a picture, the size changes too (printsize, not screensize). For example:

a image: 10 x 10 cm, 300 dpi
you change dpi to 150, the image will be 20 x 20 cm. Is this not a form of resize?

I think that a "Change DPI" would fit nice in the "resize" dialog, in addition to the current values.

Maybe I'm just used to Photoshop, but it makes more sense.
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Postby Danny » Mon Dec 08, 2008 8:55 pm

Yes, this still holds true. The Set DPI dialog is useless currently.

If you don't get any feedback on how the actual print size will turn out, changing the DPI value is pointless.

IMO it can stay in it's own dialog, but there's got to be a feedback on the print size changes.
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Postby Troken » Tue Dec 09, 2008 12:13 pm

Danny wrote:IMO it can stay in it's own dialog, but there's got to be a feedback on the print size changes.


Thank you Danny for adressing this issue again. Yes, some kind of feedback for the user would be nice.

The only reason to keep the "Set DPI" dialog would be for those who are not accustomed to the "Resize"-dialog yet.

1. Working differently
When reading this old post again, it appears to me that the problem gets more serious. We can start with the funny thing how different the "Set DPI" dialog and the "Resize" dialog works:
A. If you change DPI in "Resize", the pixelvalues change as compensation. In "Set DPI", the printsize changes instead. Somewhat inconsistent.
B. In "Set DPI" you can change X and Y individually, but not in "Resize"? Why?

2. Distorted images
So with this in mind, take this strange example: What happens if you in "Set DPI" change the X value only, say from 72 to 720 dpi? Now look in "Resize", the overall DPI is set to 720 (XnView choses to display the X DPI only, not the Y DPI). Inconsistent if you ask me, and very confusing.

3. No view update
:bug: And a bug: the image is not updated with this new dpi (720/72), it still looks like 72/72 dpi. You must trigger an action, i.e. go to "Paint" and cancel, to update the image view. Now the image in our example will be shown correct - very thin.

4. Distorted prints
This can become troublesome in the "Print" dialog as well, if you select "Single - DPI". Suddenly the image that you thought had 720 dpi gets 'distorted' and very thin, even if this actually is the correct view.

So this issue unfortunately has many side effects.
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Postby Danny » Tue Dec 09, 2008 5:57 pm

Troken wrote:Thank you Danny for adressing this issue again. Yes, some kind of feedback for the user would be nice.

It's a must have really, as you'd have to calculate it yourself. I had to deal with it yesterday, and i had to fire up Gimp since XNView didn't get me any further.

Troken wrote:The only reason to keep the "Set DPI" dialog would be for those who are not accustomed to the "Resize"-dialog yet.

1. Working differently
When reading this old post again, it appears to me that the problem gets more serious. We can start with the funny thing how different the "Set DPI" dialog and the "Resize" dialog works:
A. If you change DPI in "Resize", the pixelvalues change as compensation. In "Set DPI", the printsize changes instead. Somewhat inconsistent.
B. In "Set DPI" you can change X and Y individually, but not in "Resize"? Why?

1.A I don't see what's supposed to be inconsistent. It's a feature, not a bug.
  • Change DPI dialog -> only affects print size, no pixels are changed.
  • Resize dialog -> pixels are changed.

1.B Good question. XNView is the only program i know that's treating x and y differently btw.

Apart from that, it should be called PPI anyway, 'cause that's what they really are - pixels. Dots is what your printer spits out, which is something completely different (don't get me started ;) ).

Like i said before, it's ok with me to have a seperate "Change print size" dialog. We could even have a setting for LPI (lines per inch) in there as well.
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Postby Troken » Wed Dec 10, 2008 10:29 am

Danny wrote:
Troken wrote:1. Working differently
When reading this old post again, it appears to me that the problem gets more serious. We can start with the funny thing how different the "Set DPI" dialog and the "Resize" dialog works:
A. If you change DPI in "Resize", the pixelvalues change as compensation. In "Set DPI", the printsize changes instead. Somewhat inconsistent.


1.A I don't see what's supposed to be inconsistent. It's a feature, not a bug.
  • Change DPI dialog -> only affects print size, no pixels are changed.
  • Resize dialog -> pixels are changed.


I think it is a little confusing. If I change DPI in one of the dialogs, I would take for granted it would work the same in the other dialog, when changing the same value. I was quite suprised when I discovered this difference. I suggest it works like in the "Change DPI" dialog in both dialogs = print size is affected. Its more pedagogic too, isn't it? Change of DPI should not affect the actual pixels of the image, because such an action will resize the image (yes, even in the "Resize" dialog :) ). Ah, maybe its a question of taste?

Danny wrote:Apart from that, it should be called PPI anyway, 'cause that's what they really are - pixels. Dots is what your printer spits out, which is something completely different (don't get me started ;) ).


Yes, it is true, PPI is the correct term, but it seems it has been widely accepted with DPI (unfortunately). Perhapps only advanced users, proffesionals and other "power users" would appreciate PPI, for the rest (the majority?) it could get confusing.
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Postby Troken » Wed Dec 10, 2008 10:31 am

I wrote about this two years ago in this thread (with nooooo response, boohoo!).

viewtopic.php?t=5154
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Postby Danny » Wed Dec 10, 2008 4:02 pm

But remember that the current functionality would be lost (change PPI -> resize image, but keep print size). You can't even do that in Photoshop directly IIRC.
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Postby xnview » Wed Dec 10, 2008 4:11 pm

Troken wrote:I wrote about this two years ago in this thread (with nooooo response, boohoo!).

viewtopic.php?t=5154

Sorry i check all thread, but i can't make always a reply
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Postby Troken » Thu Dec 11, 2008 8:41 am

xnview wrote:Sorry i check all thread, but i can't make always a reply


Of course, I wasn't serious about the boohoo-part. :wink: I think you do a tremendous work in your answering of requests.
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Postby Troken » Thu Dec 11, 2008 9:05 am

Danny wrote:But remember that the current functionality would be lost (change PPI -> resize image, but keep print size). You can't even do that in Photoshop directly IIRC.


You can, under "Image size" (the Photoshop equivalent to XnView's "Resize image") you can use the check box "Resample image" to toggle between resizing print/pixel-size when changing PPI. When checked the pixel size is changed, when unchecked the print size is changed. Very handy and gives total control over PPI/pixel size/print size.

Therefore Photoshop does not need two different dialogs, you can do it all in "Image size".

In XnViews "Resize image" there is a similar checkbox called "Keep print size", which should function just as Photoshops "Resample image" I imagine. However, it does not work perfect: if you change PPI with the checkbox checked (thus keeping the print size) it will do what you expect – the pixel size is changed. But if you uncheck the box and then change the PPI, the same happens! The print size remains unchanged and the pixel size changes. Hm, thinking about it, it should be considered a bug. :bug: Pierre, what do you make of it?

If this would work correctly, I don't really see a need for the "Set DPI" dialog.
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Postby Danny » Tue Dec 16, 2008 3:50 pm

No, i just double-checked with Photoshop.

XNView: Keep print size = off
Pshop: Resample image = on
-> both programs behave in the same way
-> good.

XNView: Keep print size = on
Pshop: Resample image = off
-> both programs behave differently
-> good as well.

Why? Because it's not the same feature! PShop fixes the images' dimensions in pixels, while XNView fixes the images print size in pixels per inch (or cm).

You can't do the one thing in the other program. That's why i said enhance the change DPI dialog with the feature from Photoshop and we're going to have the best of both worlds.

Or include another checkbox to fix the image's pixel dimensions in the resize dialog. Then we could indeed drop the "change DPI" dialog altogether.
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Postby xnview » Tue Dec 23, 2008 9:49 am

So :-)
You would like in 'Resize', when you change DPI that 'Print size' change (if 'keep print size' not checked)??
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Postby dee » Fri Dec 26, 2008 12:39 am

xnview wrote:So :-)
You would like in 'Resize', when you change DPI that 'Print size' change (if 'keep print size' not checked)??

Yes, and also vice versa (when user changes Print size, change DPI).
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