Author Topic: Howto set document desired dpi  (Read 5673 times)

Pshem

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Howto set document desired dpi
« on: October 26, 2015, 11:35:28 pm »
Hello there. I've just installed Scribus and encountered an issue right away - how do you set documents resolution (dpi)? Can't find it anywhere , and it seems the setting is fixed at 72dpi.

GarryP

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Re: Howto set document desired dpi
« Reply #1 on: October 27, 2015, 12:17:59 pm »
Hello Pshem, and welcome to the forum.

Scribus documents - and the PDFs created from them - don't have a DPI. Everything except bitmap (raster) images is in vector format and so has no resolution. Text, shapes, bezier curves and all of that stuff can be infinitely scaled (up to a point).

What you might be having an issue with is the resolution of a bitmap.

With the image selected go to "Properties / Image" and check the Actual X/Y-DPI values. If your image is at 100% scale and the DPI values are 72 then your image was created to be seen at 72 DPI. There's no way to increase the "resolution" of an image to a higher value than what it is at 100%. Something like GIMP will let you change the DPI but it will make no difference; there's just not enough detail to do anything with. You can make the image smaller to increase the apparent DPI but obviously your image may not be the right size after that.

The DPI of an image is no more than a "recommendation for display purposes". It still has the same number of pixels regardless of how many there are per inch.

You can also look at "Document Setup / Tools / Image" and make sure that the preview is set to "Normal Resolution" instead of "Low". Right-clicking an image frame and looking at the "Preview Settings" menu will also tell you what the preview setting is for that image frame.

If none of that works then please give more details as to where you think the problem is. It may not actually be a problem in the first place, and might just be a misunderstanding.

Nermander

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Re: Howto set document desired dpi
« Reply #2 on: October 27, 2015, 03:56:08 pm »
A bit more clarification: Scribus primary target is print. For printed media you define a physical size. You can set a size for your document.

The DPI (or rather PPI) is then just a relation between the number of pixels in an image and the physical size. You can not change the DPI (or PPI) without changing either the number of pixels or the physical size.

Pshem

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Re: Howto set document desired dpi
« Reply #3 on: October 28, 2015, 12:04:34 am »
thx guys.
But got to admit I'm still confused. Yes, I expected to work in real world units - but to my surprise the default templates use points (?).
Also whenever you need to print something , no matter when you use vectors or raster you need to set print dpi.

I've got even more confused when I've started importing some raster images to the Scribus page. Default layout is 595x841 points (A4 at 72dpi) . When I've pasted a raster 4960x3508 (which makes an A4 page at 300ppi) it pastes like a crazy huge object. So it still seems there's some background setting set to 72dpi (which is way too low).

Also I've been wondering whether Scribus can give me a realtime feedback when resizing the frame / image . Quite often I need to match the items that are on raster image with the curves that are on different layer (they need to align), so the plotter cutter could do the correct cuts (cuts are guided by the cuves). Now I can see how much space the frame will take in realtime, but the image itself resizes / transforms only after I commit the change.

Lastly - can I import pages from pdf with curves, or do I need to open in Inkscape first , convert to svg for example then open in Scribus?

Ahhh.... starting a completely new app can be so daunting at times... But I'm committed to maek it work - Scribus seem like a tool that should be great for my needs (preparing pages for the ploter).

Nermander

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Re: Howto set document desired dpi
« Reply #4 on: October 28, 2015, 09:00:59 am »
But got to admit I'm still confused. Yes, I expected to work in real world units - but to my surprise the default templates use points (?).
You can change the units in the preferences. The points are postscript points, but you can use, mm, cm, pica, inches or whatever you like from what Scribus supports.
http://wiki.scribus.net/canvas/Help:Manual_Configprefs#Document

It seems as if you are confusing postscript points with pixels? A postscript point is 1/72 of an inch.
https://en.wikipedia.org/wiki/Point_%28typography%29#Desktop_publishing_point


GarryP

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Re: Howto set document desired dpi
« Reply #5 on: October 28, 2015, 12:29:02 pm »
Pshem, I think can see where the confusion is coming from.

Points are real world units, as are inches, millimetres, etc. Pixels are not real world units.

Pixels only exist in the computer. A raster image is made up of a grid of pixels which are indivisible elements of the image. A pixel in an image has no inherent size; it is just a unit of information which tells the computer how that small part of the image should be displayed.

An A4 page is - as you said - 595 points wide by 841 points high (give or take) however, in itself, it has no Dots Per Inch (or Pixels Per Inch) measurement. It has a size but no resolution.

Every image is stored with a recommendation as to how it should be displayed. This is the DPI (or PPI) of that image as it exists in the file (this is important to note). If an image has a DPI(PPI) of 72 then it is saying that it should be displayed in a way that 72 pixels should cover one inch. In other words, a 72x72 pixel image at 72DPI(PPI) should be one square inch in size. (The size it will actually be on your screen depends on many things that are outside the scope of this explanation.)

If, as you have said, you have an image that is 4960x3508 and that image has a stored (on the file) resolution of 300DPI then that image will - when put in an image frame - be 4960/300=16.53 inches wide by 3508/300=11.69 inches high.

If you put this image into an image frame that covers your A4 page (which is 595 points x 841 points in size, which works out at 8.26 x 11.68 inches - at 72 points in an inch) then the image will be about twice the width of the image frame while the height will be about the same.

If your image was 72DPI rather than 300DPI then it would be much larger than the image frame (or page) at 68.88 inches wide by 48.72 inches high. (This would be "crazy huge".) On the other hand, if your image was 3000DPI then it would be just 1.65 inches wide by 1.16 inches high, probably way too small to make out any details.

By default, Scribus always displays images in image frames with deference to the resolution which is stored in the image file unless you have the image scaling set differently in "Preferences (or Document Setup)/Tools/Images".

However, if you select your image frame and go to "Properties/Image" you should see the "Actual X/Y-DPI" values. If the X/Y-Scale values are both 100% then the Actual-X/Y DPI will be whatever was stored on the file. If you change both the X/Y-Scale values to 50% the Actual-X/Y DPI values will double and the image will be displayed at quarter the size. Conversely, making the Scale values larger will make the DPI values smaller and the image will be displayed larger. Scribus can only display images at the resolution that is set in "Properties/Image".

Larger scale = lower visible resolution (DIP/PPI) and smaller scale = higher visible resolution but that's just the resolution of the image as it's seen on the screen or would be printed on paper. You don't actually change the resolution of the image itself, you only change the resolution of how it will be displayed/printed.

The thing to keep in mind is: Pages don't have a resolution/DPI/PPI but images do. A page has no concept of a resolution, it is just somewhere to put images that do.

I hope this helps to explain things a bit better.

Pshem

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Re: Howto set document desired dpi
« Reply #6 on: October 28, 2015, 09:46:16 pm »
ahhh... that makes sense now. Term "points" is used on some times in exchange with pixels - while in dtp world its a different term. THANK YOU!

As for image - I'm pretty sure it has correct resoloution. When I open it in Krita, or some other apps and when I check real world dimension I get A4 equivalent.

So now I've been wondering about scaling/transforming images - while I know I can ctrl+drag to get proportional change on both axis, where can I check whether the proportions are ok? Can those be changed using number values? I fear I may distort the image accidentally .
Also is there a way to fit the image inside the frame, but keeping the proportions?

Is there a way to combine 2 pages? For example if I do 2 A4 pages and then decide that I should have gone with single A3 instead how would I approach it?

Lastly - can I import pages from pdf with curves, or do I need to open in Inkscape first , convert to svg for example then open in Scribus?

Nermander

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Re: Howto set document desired dpi
« Reply #7 on: October 29, 2015, 09:29:53 am »
For the size and aspect ratio, check the properties palette (brought up with F2). The properties palette is one of the most important features in Scribus.


As for combining, there are generally two alternatives.

First is to change the size of one of the pages in Scribus (maybe also move its content to one side) and then cut and paste the content from the other page (and finally delete the now empty page). Pages in a document can have different page sizes so there is no problem making page 1 A3 landscape while keeping page 2 A4 portrait.

The second is to imposition the pages after creating a PDF.
http://wiki.scribus.net/canvas/PDF,_PostScript_and_Imposition_tools

GarryP

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Re: Howto set document desired dpi
« Reply #8 on: October 29, 2015, 11:41:59 am »
In the Properties Palette, if you want to keep the proportions of an image - or frame or shape - then you need to make sure that the little "chain" icon to the right of the size/scale values is activated (the links of the chain will be linked when activated). That way, Scribus will automatically change one value in proportion to the other value that you change yourself. (Note that this "proportional linking" in the PP only works for changes made in the PP, it doesn't affect dragging actions.)

Be aware that you need to make sure that you have this icon activated as soon as - or before - you create the frame or add the image, otherwise you could change one value by itself and then switch on "proportionality" which will then calculate with the wrong set of non-proportional values. This is easier to see for yourself than it is to explain so just try it.

As for getting curves from a PDF, you can import a PDF into an image frame (setting the desired page number in "Properties/Image") but the stuff in the PDF cannot be referenced in the rest of the document. For example, you can't align a frame/shape outside an image frame to something within an image frame. If you need to use something within the PDF as a reference then you'll need to find some way of extracting it from the PDF and then importing that into Scribus (probably as an SVG). On the other hand, if the curve isn't very complicated you could always use the bezier tool to trace over the image frame containing the PDF then remove the PDF when you're done.

 

palmate