question on default DPI

[srg]

Can anybody tell me why my AP file are by default opened at 300 DPI and at times at 96? This is very upsetting since the resizing function is slow and at times buggy. Thanks

[GarryP]

I think this probably depends on what you mean by “opened”.
When you create a new Photo document (AFPHOTO) you have the option to set the DPI and that should not change without your say so, either by specifically changing it or using a function which changes it. When you open a Photo document it should have the DPI you told it to have, by whichever method you told it. If the DPI changes without you doing something to make that happen then that could be a problem.
If you open an image (JPG/PNG/GIF/etc.) then Photo will normally take the DPI setting from the metadata of the image, if there is one.
If you open an image and it has no metadata then I’m not sure what DPI Photo will give it by default but it is likely to be either 72 or 96 (I think this depends on the OS but I’m not totally sure about that).
Does any of this help?

[Pšenda]

37 minutes ago, GarryP said:

If you open an image and it has no metadata then I’m not sure what DPI Photo will give it by default but it is likely to be either 72 or 96 (I think this depends on the OS

I think it works like that in "New from Clipboard".

[GarryP]

Ah, I never thought about that option.
I’ve just done some basic tests with two images: (1) with metadata of 300DPI; and (2) with no DPI metadata.
Opening image 1 in Photo gave me a document DPI of 300, as expected.
Opening image 2 in Photo gave me a document DPI of 72, it’s got to default to something.
I then created a new Designer document with DPI set to 300.
Placing image 1 into this document, copying it, then using “New From Clipboard” in Photo gave me a new document DPI of 96.
Exactly the same thing happened with image 2.
So, on Windows at least, and with these two random images:
* opening an image with no DPI metadata gave a new document of 72DPI;
* opening an image with DPI metadata gave a new document with the DPI the same as in the metadata;
* using “New From Clipboard” with either image gave new document of 96DPI.

[Pšenda]

Setting up DPI by image source is quite logical (known source = DPI defined by metadata, unknow source = 72, OS/Clipboard = 96), but it may still be an unpleasant surprise.

 

 

[srg]

What I do is take photos with the same camera in .DNG (a Pentax K1 II, excellent camera BTW) then I develop in AP or use more photos for a focus merge and then start working on the resulting file. At times ( the great majority) I get a 300DPI file at times a 96 DPI file.

The problem is that if I forget to check and eventually change  (resize) the image/file I find myself in trouble since a much worked image can be very big and difficult to resize.

I hope this will clarify what I mean. 

I wish some of the staff will chime on this.

[Dan C]

My apologies for the delayed response srg, as we have been closed over the holiday period.

On 12/20/2019 at 10:23 PM, srg said:

then I develop in AP or use more photos for a focus merge and then start working on the resulting file. At times ( the great majority) I get a 300DPI file at times a 96 DPI file.

Are you finding differences in DPI after developing images, or only when creating stacks?

If it's the latter, do you have a set of images that each time creates a stack at 96 DPI?

[Medical Officer Bones]

DPI (or actually PPI in this case, but Affinity gets the terminology wrong) doesn't say anything about the actual resolution of your files. It is merely a parameter that tells software at what size it will be printed.

To learn what is happening in your workflow, we also must know whether the resolution in pixels is changing or not in your files.

If this is not the case, then the PPI parameter in the Affinity file is somehow changed at some point in your workflow.

So: do the 300ppi and 96ppi files differ in pixel dimensions, or not?

 

[srg]

4 hours ago, Dan C said:

My apologies for the delayed response srg, as we have been closed over the holiday period.

Are you finding differences in DPI after developing images, or only when creating stacks?

If it's the latter, do you have a set of images that each time creates a stack at 96 DPI?

Hi Dan, I do not check regularly the DPI after developing or focus merging but I believe it happens both after developing from RAW and focus staking raw images.

 

[R C-R]

18 hours ago, Medical Officer Bones said:

DPI (or actually PPI in this case, but Affinity gets the terminology wrong) doesn't say anything about the actual resolution of your files.

FWIW, I have always thought that neither DPI nor PPI are particularly appropriate for describing the inherent (a.k.a. "actual") resolution of files. That is because both DPI & PPI refer to measurements that have clearly defined, unambiguous meanings only in some physical context. So for example, while PPI is entirely appropriate & well defined when the reference is to the resolution of a computer monitor or any other pixel-based physical display device, it fails to clearly & unambiguously define how any object in a document file might be rendered on that device.

Among other things, vector objects are inherently resolution independent so it does not make any sense to talk about the 'actual' PPI of that kind of file object.