Should changing the DPI of the document change the size of a document page?

[shushustorm]

Didn't read everything, but:

Going from 300DPI to 72DPI, you're spreading the pixels 300/72 as wide. 300/72=4,166..

So 100mm becomes 416,66mm. Seems reasonable to me. If previously different, seems like a fixed bug from V1 to V2.

Unless, of course, I missed that you want to resample. In that case, pixel count changes and real world dimensions stay the same.

[R C-R]

1 hour ago, shushustorm said:

Seems reasonable to me. If previously different, seems like a fixed bug from V1 to V2.

Then why does it behave differently in 2 of the 3 V2 apps?

It's a bug!

[shushustorm]

I'd say there's a checkbox missing to choose resampling or not. If not chosen, this topic's behaviour should be normal. If it is, the pixel count should change instead. That said, with the option missing entirely, I'd say it makes more sense to change the size than the pixel count, because why would you lower DPI? To get more real world space. Besides, changing pixel count is destructive and if used incorrectly, will lead to data loss. And if you're purely using data digitally, DPI as well as real world size aren't relevant at all, since the display specifies that, not a file. (Needless to say, it's quite confusing having the export persona depend on DPI settings. But that's a different matter.)

EDIT:

Oh wait, there is a Resampling feature. So yes, the results discussed here are to be expected when Resizing.

As stated in the docs:

"

Scaling

Scaling will embed a specific print resolution into an image's metadata to force it to print at a specific dpi (e.g. 300 dpi). The image's pixel dimensions remain unaffected.

"

(source: https://affinity.help/photo2/en-US.lproj/index.html?page=pages/SizeTransform/imageSize.html?title=Changing image size , underlined by me)

If DPI changes and px is constant, real world size must change:

DPI = px / inch

Not a bug, but expected. And, if you're asking me, it makes perfect sense.

[lepr]

26 minutes ago, shushustorm said:

[...] (source: https://affinity.help/photo2/en-US.lproj/index.html?page=pages/SizeTransform/imageSize.html?title=Changing image size , underlined by me) [...]

You're looking at the help for Photo, but this thread is concerned with broken functionality in Publisher.

A Resample checkbox is appropriate for Photo because that app destructively resamples Pixel objects when the document's size measured in pixels is scaled.

A Resample checkbox would be inappropriate for Publisher (and Designer) because these apps non-destructively scale Pixel objects when the document's size measured in pixels is scaled.

 

[shushustorm]

3 minutes ago, ,,, said:

non-destructively scale Pixel objects 

That would be just a further argument for why it changes real world dimensions rather than px count. And one of those has to  be changed when changing DPI.

[lepr]

11 minutes ago, shushustorm said:

That would be just a further argument for why it changes real world dimensions rather than px count. And one of those has to  be changed when changing DPI.

Publisher 2 just needs to do the same as the current Designer 2, which is what both Publisher and Designer did in v1.

That is, honour the user's choice of whether physical size or pixels quantity changes when DPI is changed, as was the case until version 2.

 

[shushustorm]

8 minutes ago, ,,, said:

That is, allow the user to choose whether physical size or pixels quantity changes when DPI is changed, as was the case until version 2.

That's what I said:

51 minutes ago, shushustorm said:

I'd say there's a checkbox missing to choose resampling or not.

I just don't think the result for the given input is surprising and, given that your point, just as mine, was to have non destructive results, - when not given an option - changing real world dimensions makes more sense than changing px count. That's all I said. But, let's see if Serif answers this. Doesn't make a lot of sense discussing without official statements whether there just might be a checkbox missing or not.

[lepr]

[deleted - sick of arguing]

[R C-R]

The behavior should be the same in all 3 apps if for no other reason than all 3 of them can open & edit a document created in any one of them. So it would be absurd if it behaved one way in APub but another if the same document was edited in any of the others via File > Edit in..."

[MikeTO]

7 minutes ago, R C-R said:

The behavior should be the same in all 3 apps if for no other reason than all 3 of them can open & edit a document created in any one of them. So it would be absurd if it behaved one way in APub but another if the same document was edited in any of the others via File > Edit in..."

You've nailed the issue. In v1 all the apps work the same way - if you changed the DPI of a non-pixel document the physical size of the document wouldn't change regardless of the app you used. But in Publisher v2, changing the DPI changes the physical size of a non-pixel document. Doing the same thing in Photo does not change the physical size. This is a bug in Publisher v2.

[R C-R]

2 minutes ago, MikeTO said:

But in Publisher v2, changing the DPI changes the physical size of a non-pixel document.

The only thing being changed is the UOM (unit of measurement) of the document, like among mm, px, inch, or whatever. That should never change the dimensions of the document, just the units used when setting or displaying them.

So it isn't really about a "non-pixel document" vs. a pixel-based document. It is just about a bug in one of the V2 apps that needs to get fixed.

[shushustorm]

17 hours ago, R C-R said:

The behavior should be the same in all 3 apps

Everyone wants the same behaviour in all Affinity apps, yet I mustn't quote the Photo docs, which clearly state the issue mentioned here is intended.

17 hours ago, MikeTO said:

a non-pixel document

What's a non-pixel document? Any document not made of vectors or text data is made of pixels. Do you mean a document that, within the document setup, has one of the real world sizes set for editing?

17 hours ago, R C-R said:

The only thing being changed is the UOM (unit of measurement) of the document, like among mm, px, inch, or whatever. That should never change the dimensions of the document, just the units used when setting or displaying them.

I really tried understanding this, but I have no clue what this is supposed to mean. The first sentence mixes real world dimensions and pixel counts, which don't compare. The second sentence, if taken by its words, would mean that, for example, mm change to m instead of changing the values, which I don't think would make sense in any case, nor that you meant it like that, yet I fail to interpret it differently.

All I can say, and that for certain, a

DPI decrease either means

- real world size increase (1) or

- pixel count decrease (2) (loss of data)

because

pixel density [dpi] = number [px] / distance [inch]

and that, typically, you can choose between resizing (1) and resampling (2), leading to the according changes.

Despite seeming different opinions I find this exhausting just like ,,,. So I'm out of here as well.

[NotMyFault]

I get the impression that several topics get mixed up in this and other threads covering the topic.

In essence, we have a set of different functions, which deal with document size in number of pixel, Physical size (pt, mm, inch, ….) and DPI

Resize Canvas (pages, spread, …):

1. resize canvas: DPI is constant, number of pixels and physical size change by identical factor. If you add/subtract, this gets converted to a factor. Former content keeps its size, but canvas is extended

All content stays untouched, but gets repositioned based on chosen anchor point

Resize document with resample:

1. change number of pixels. ( if using px) DPI stays constant.
2. Change size in physical unit (if using phys unifs). DPI stays constant.
3. change DPI while using physical units: resamples number of pixels

All content gets either scaled (vector) or resampled (raster)

Convert units of measurement:

1. change units: number of pixel and DPI stay constant, physical sizes is re-calculated
2. change from pixel to physical unit:
3. change from physical unit to pixel

All content and document size stays untouched, only units of measurement gets converted

UI in Photo, Designer, Publisher

The 3 apps totally differ in UI how you can trigger these functionality, and some constraints apply like dealing with integer or decimal numbers for pixels.

A volunteer might create a big table covering all 6 functions * 3 apps * 2 versions * 3 platforms minus 1 (Publisher V1 iPad) = 107 variants so everyone can see every operation is possible in every app, if you find the correct way to use the UI.

During Export, you have the option to change the size again (resample), or choose to export certain parts of document only (selection, Artboards, Pages)

One closing remark:

don't change too much in one step. Either resize, or change units, or change DPI w/o resample. If you want to change multiple things, do it in 2 steps.

Edited January 29, 2023 by NotMyFault
Minor corrections.

[NotMyFault]

and to answer the original question of the thread title:

Should changing the DPI of the document change the size of a document page?

You have the absolute choice by checking or unchecking "Resample" 

In Publisher:

File->Document Setup->Scaling

• Set either to rescale or one of the 2 other options

 

 

[lepr]

2 hours ago, NotMyFault said:

and to answer the original question of the thread title:

Should changing the DPI of the document change the size of a document page?

You have the absolute choice by checking or unchecking "Resample" 

In Publisher:

File->Document Setup->Scaling

• Set either to rescale or one of the 2 other options

 

 

 

Nope. Doesn't help, not the subject of this thread, and likely to cause confusion.

The Scaling controls determine what is to happen to objects in the document when the document dimensions change. (By the way, the resample method there is redundant - when scaling happens, it is nondestructive and involves no resampling. Photo is the only Affinity app that destructively resamples Pixel objects when a document has its pixel dimensions scaled.) 

Whereas, this thread is about Publisher 2's broken means of preventing the document changing physical size when DPI is changed.

[R C-R]

7 hours ago, shushustorm said:

I really tried understanding this, but I have no clue what this is supposed to mean.

What it means is it does not matter if you specify values using physical units like mm or just pixel values; the apps will accept values using any of them. In fact, you can change the document units at any time by right-clicking on the origin of the ruler when it is displayed (where it says mm or px or in or any of the other supported unit types) & choosing one of the others from the popup menu.

Doing this should not & does not in any of the apps except Affinity Publisher V2 change the dimensions of the document.

[lepr]

Hopefully, the following will make clear what is working and broken (red text) in the 3 apps.

Versions 1 & 2 of Publisher and Designer (in Document Setup window)

• Broken in Publisher 2 only - to maintain document physical dimensions when changing PPI: set document units to physical then change PPI
• To maintain document pixels dimensions when changing PPI: set document units to pixels then change PPI

Versions 1 & 2 of Photo (in Resize Document window)

• To maintain document physical dimensions when changing PPI: ignore document units, enable Resample then change PPI
• To maintain document pixels dimensions when changing PPI: ignore document units, disable Resample then change PPI

[shushustorm]

Alright, last post of mine here, since I now do understand what you mean, yet I find @R C-Rs wording somewhat confusing. You do mean it does matter whether you choose mm or px, right? Because you do think, depending on the chosen unit, it should behave differently and keep the chosen unit unchanged, whereas the other factor (be it pixel when mm is chosen or mm when px is chosen) changes. If that is the intent of this topic, then yes, alright, it may be a bug. Still I do think if that's really intended, it's highly obfuscated (no word of resampling anywhere) behaviour for something that's possibly a document crippling operation with loss of data.

[lepr]

2 hours ago, shushustorm said:

You do mean it does matter whether you choose mm or px, right? Because you do think, depending on the chosen unit, it should behave differently and keep the chosen unit unchanged, whereas the other factor (be it pixel when mm is chosen or mm when px is chosen) changes.

Yes, that's how AD1, AD2 and APub1 work, but APub2 is broken.

APub2 currently always maintains the pixels dimensions and changes the physical dimensions when PPI is changed, regardless of the document units being pixels or physical. APub2 currently does not allow the user to maintain the document's physical dimensions when changing PPI. It seems illogical for that loss of functionality to be a design decision of the developers, therefore it's most likely a bug.

2 hours ago, shushustorm said:

Still I do think if that's really intended, it's highly obfuscated (no word of resampling anywhere) behaviour for something that's possibly a document crippling operation with loss of data.

As I said earlier, AD and APub do not resample Pixel objects when the document's pixels dimensions change, therefore there is no "document crippling" and no reason to mention resampling. Instead, these apps nondestructively scale Pixel objects when the document's pixels dimensions change. Only Photo destructively resamples Pixel objects when the document's pixels dimensions change, and there is a Resample checkbox in Photo.

[R C-R]

5 hours ago, shushustorm said:

...yet I find @R C-Rs wording somewhat confusing.

Did you try what I suggested about changing the document's units, for instance using the pop-up menu in the document ruler? If you do that, neither the dimensions nor the DPI of the document change because for that it does not matter which units the document uses.

[stokerg]

Hi @GarryP,

I've just replicated this here and have double checked with QA who confirm this is a bug and I've just got this logged with the Dev team  

Did you post a separate bug report for this issue?  If so, please link me to that thread and I'll make sure that thread is updated and the Support Ticket for it closed.

[GarryP]

I’d completely forgotten about this – thanks for picking it up.
I’m pretty sure that, if I hadn’t forgotten about it, I would have added a link to a bug report if I had made one so I think it’s reasonable to assume that I just didn’t get round to adding one.

[stokerg]

3 minutes ago, GarryP said:

I’d completely forgotten about this – thanks for picking it up.
I’m pretty sure that, if I hadn’t forgotten about it, I would have added a link to a bug report if I had made one so I think it’s reasonable to assume that I just didn’t get round to adding one.

No problem, I did do a search of the Forums and couldn't spot a report in bugs for this but thought I'd double check  

[Affinity Info Bot]

The issue "Changing the DPI of a document using any unit, other than pixels, cause the page to change size" (REF: AFB-7395) has been fixed by the developers in internal build "2.1.0.1720".
This fix should soon be available as a customer beta and is planned for inclusion in the next customer release.
Customer beta builds are announced here and you can participate by following these instructions.
If you still experience this problem once you are using that build version (or later) please reply to this thread including @Serif Info Bot to notify us.