Re: #tdf51510: Change the DPI to get better resolution, but failed the unit test

[Tomaž Vajngerl <quikee@xxxxxxxxx>]

Hi,

On Tue, Aug 29, 2023 at 9:09 AM Lodev <lodev@xxxxxxxxxxxx> wrote:
> Sorry if I'm asking a stupid question here.  First, I've never seen or
> used a document with "multiple instances that all point to the same
> image in the document".

That's easy - drag the image while holding ctrl and drop. It will make
a copy of the Graphic, but it still references the same instance and
you can resize each one independently. If you save the document there
will be only one image saved.

> And I take "the image in the document" or "The
> size the image takes up in the document" seems to be the "Apparent
> dimensions", 4.24" in this case.  Is it?

Yes - the document has a size and combined with the size of the image
(in the document, not what it is set in SVG) you can calculate the
actual needed DPI relative to the document.

> That is, even if there are
> multiple images in this document which the source is the same one (I
> still don't know how to do that), shouldn't it be calculated regarding
> to the "Apparent dimensions" here?  I mean, after all, that is what user
> set in the document.

That's the point - what is important is the size of the image in the
document, not what the size is the SVG image.

>  Since the image shown in the document is actually
> 4.24"x4.24", while the original svg file is 0.21"x0.21, shouldn't it be
> 20 times (4.24/0.21 ~= 20) DPI, that is, 96*20 = 1920 sent to xBitmap()?

Yes, that seems correct. But this is only for this case - another case
would need another factor. For example if you resize the image in the
document to 0.42 x 0.42, you would use the factor 2.

> We tried to set Size(20,20) to get aDPI, or directly set aDPI to
> (1920,1920), they both ended up 4.24"x4.24" with 99DPI, which is good
> enough.  Do you think it a reasonable thought?

That's only for this image where 20 is correct - you would need
another number calculated per image. Also use a constant DPI factor as
I already said at the beginning, not the size of the output device.

> > So you will need to first find the place where conversion for the
> > embedded PNG and properly calculate the size at that place - not
> > inside this method.
>
> The size should be the Apparent dimensions, since in the document it was
> set to that size.  That's what we thought.

Yes - it needs to be the size in the document, not the size of SVG.

> BTW, if so, how can we get the Apparent dimensions in this method?

You will have to set it from the outside as a parameter - as it
depends on the image and here you don't have the information.

> Thanks for your reply,

Tomaž