Confusing Use of DPI

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Eidolon
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Confusing Use of DPI

Post by Eidolon » Wed 20 Feb 2008 08:34

Hello. I'm testing PhotoLine and considering purchasing it. But I don't understand one aspect.

Apparently, new documents have a fixed DPI of 300. Is there any way of changing it? And this DPI confusingly affects the scale of items added to a document.

For example, suppose I have a 150 DPI photo that is 2 inches wide. If I drop it onto a document set to 300 DPI, I expect the photo to measure 1 inch wide (a pixel-to-pixel match). But when I do that operation in PhotoLine, the photo is scaled up to 200%. This scaling presumably involves interpolation and thus affects the integrity of the image. How do I prevent it?

Another example: if I draw a vector shape on a document in PhotoLine and set the drawing to 600 DPI, the document changes to half its size in inches. I thought I was creating an 8.5 x 11 inch page, and suddenly it's 4.25 x 5.5 in. How do I prevent that?

I'm sure that there is a way to work with PhotoLine without these problems. Can anyone clarify the underlying philosophy of the program?

Thanks.

Martin Huber
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Re: Confusing Use of DPI

Post by Martin Huber » Wed 20 Feb 2008 15:08

Eidolon wrote:Apparently, new documents have a fixed DPI of 300. Is there any way of changing it?
No, in document mode the dpi value is always 300. Why do have to change it?
Eidolon wrote:And this DPI confusingly affects the scale of items added to a document.
PhotoLine has two working modes:
- document mode: in document mode you start with an empty page without any layer, and you can create additional pages. In this mode PhotoLine behaves like other DTP applications and uses a combination of the pixel size and the dpi to calculate the image size, when an image is added to the document. The dpi of the document is always 300.

- picture mode: in picture mode there is a background layer, which always has to be an raster image. The size and the dpi of the background layer are used for the whole document, so the document will always have the same size and the same dpi as the background layer.
Eidolon wrote:For example, suppose I have a 150 DPI photo that is 2 inches wide. If I drop it onto a document set to 300 DPI, I expect the photo to measure 1 inch wide (a pixel-to-pixel match). But when I do that operation in PhotoLine, the photo is scaled up to 200%.
Yes, in document mode this will happen (like in other DTP applications).
Eidolon wrote:This scaling presumably involves interpolation and thus affects the integrity of the image.
This scaling doesn't modify your pixel data and doesn't affect the integrity of the image.
Eidolon wrote:How do I prevent it?
After insertion you can use "Layer/Layer Properties/Extended" to reset the scaling to 100%.
Eidolon wrote:Another example: if I draw a vector shape on a document in PhotoLine and set the drawing to 600 DPI, the document changes to half its size in inches. I thought I was creating an 8.5 x 11 inch page, and suddenly it's 4.25 x 5.5 in. How do I prevent that?
This shouldn't happen. In fact there shouldn't be an editable dpi-field at all, if the active layer isn't an pixel image. We will change this.

Martin

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greenmorpher
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Re: Confusing Use of DPI

Post by greenmorpher » Wed 20 Feb 2008 23:21

Hello Eidolon and Martin

Eidolon -- bear in mind that everything in PhotoLine is layers. If you make a vector graphic and you select it, you are selecting its layer. You can specify that that layer be 600 dpi by going menu bar|Layer|Layer Properties and set the resolution there. It will not change the size of the graphic.

Note that if you make a graphic with several different parts to it, you actually have as many layers as you have parts. You select them all using the Layers palette (Menu Bar|View|Dialogs|Layer/Channels -- I have mine open by default) and reduce to one layer (Menu bar|Layer|Reduce to one layer).

I haven't struck the handling of pictures you describe, frankly, but I find in importing a picture into a document, it comes out at some sort of size, I don't quite know why, and when selected, tells me it is 90 dpi (my screen resolution -- set it in the Preferences (Menu bar|File|Preferences|Display|Screen Resolution). There seems to be no problem setting a higher resolution in Layer Properties.

What I do is open photos in the image window and set all the parameters there -- resolution in Layer Properties and size in Menu Bar|Layer|Scale Layer. Set the resolution first.

PhotoLine has exceptionally good interpolation stuff, by the way.

Cheers, Geoff

Geoffrey Heard, Business Writer & Publisher

"Type & Layout: Are you communicating or just making pretty shapes" -- Revealed! The secrets of how you can use type and layout to turbocharge your messages in print. See the book at http://www.worsleypress.com

Eidolon
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Re: Confusing Use of DPI

Post by Eidolon » Fri 07 Mar 2008 07:01

Martin Huber wrote:No, in document mode the dpi value is always 300. Why do have to change it?
Here is one case. When I create a PDF slideshow through Slideshow > Export, the images in the PDF are apparently converted to 300 dpi (without being resampled). I started with 200 dpi images and assigned a background TIF at 200 dpi, but the result was 300 dpi. The pixel dimensions are not changed: the pictures just print smaller.

If, instead, I choose Slideshow > OK, I can save the PL document as PDF and set a dpi. But then the images are resampled within a fixed print size determined by 300 dpi.

In either case, there's no escaping a print size set by 300 dpi.

I'd like to be able to start with a 200 dpi image that is 800 px wide and know that it will print 4 inches wide in the output slideshow PDF.

Martin Huber
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Re: Confusing Use of DPI

Post by Martin Huber » Sat 08 Mar 2008 16:00

I'm not sure, that I completely understood the problem you are describing here, so my answer may be off-topic.
Eidolon wrote: Here is one case. When I create a PDF slideshow through Slideshow > Export, the images in the PDF are apparently converted to 300 dpi (without being resampled). I started with 200 dpi images and assigned a background TIF at 200 dpi, but the result was 300 dpi. The pixel dimensions are not changed: the pictures just print smaller.

If, instead, I choose Slideshow > OK, I can save the PL document as PDF and set a dpi. But then the images are resampled within a fixed print size determined by 300 dpi.
Usually neither printing nor saving as PDF are resampling images. Resampling only takes place if one of the following conditions is met:
- There are properties, that can't be exported correctly (like transparency or perspective transformation).
- With PDF you can define a standard resolution. Images with a higher resolution will be resampled to this standard resolution.
Eidolon wrote:In either case, there's no escaping a print size set by 300 dpi.

I'd like to be able to start with a 200 dpi image that is 800 px wide and know that it will print 4 inches wide in the output slideshow PDF.
I think, the behaviour you are seeing results from the way the slideshow is working. As the slideshow is intended to produce results viewed on the screen, it doesn't work with physical units (like inch or centimeter) but only with pixel sizes. So if an image is inserted in the slideshow, its dpi are ignored and only its pixel size is used.
If - with your example of 800 px and 200 dpi - you would modify the dpi of the document created by the slideshow funtion, this image would have the correct size, but if there was another image with - for example - 300 dpi, this one would have the wrong size.

If you need the correct phyical size, I recommend to create the document manually und insert the images by using the Browse-function and centering them with the alignment tools.

Martin