Hugin halves my DPI from 300 to 150 causing loss of quality. How do I change this?

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tda...@gmail.com

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May 13, 2014, 12:57:53 AM5/13/14
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I scanned an A2 sized electrical schematic with an A4 scanner in 12 pieces, and tried out Hugin to stitch them together. The result is very promising but there is one problem - the DPI has been changed from 300dpi to 150dpi resulting in a smaller image and some loss of quality.

Of course I have read http://hugin.sourceforge.net/docs/manual/PPI.html but before anyone starts telling me how this does not affect image quality etc please view the attached files and see for yourself how the quality has been degraded.

I did try changing the DPI setting of the file back to 300dpi using Gimp but this made no difference.

How can I tell Hugin (or its processor program) NOT to change the resolution down to 150dpi and rather keep it at 300dpi?
Original scan 300dpi.png
After Hugin at 150dpi.png

Terry Duell

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May 13, 2014, 2:55:04 AM5/13/14
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Hello,

On Tue, 13 May 2014 14:57:53 +1000, <tda...@gmail.com> wrote:


>
> How can I tell Hugin (or its processor program) NOT to change the
> resolution down to 150dpi and rather keep it at 300dpi?
>

In the Stitcher tab, try selecting "Calculate Optimal Size", and see if
that helps.

Cheers,
--
Regards,
Terry Duell

Marius Loots

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May 13, 2014, 3:23:03 AM5/13/14
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Hallo,

Tuesday, May 13, 2014, 8:55:04 AM, you wrote:
>> How can I tell Hugin (or its processor program) NOT to change the
>> resolution down to 150dpi and rather keep it at 300dpi?

Terry> In the Stitcher tab, try selecting "Calculate Optimal Size", and see if
Terry> that helps.

In my experience, both the above as well as in
Preferences - Assistant Tab - Downscale final pano = 100% of final
width.

Groetnis
Marius
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panostar

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May 13, 2014, 6:06:07 AM5/13/14
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There will always be a difference between the original image and the stitched image owing to the interpolation process that has been used to remap the image to and from the spherical stitching surface.  There are several interpolators to choose from and there can be quite big differences between them, depending on the nature of the image.  It would be worth trying some of the alternatives.  Needless to say, the dpi/ppi has no effect whatever on the image quality.  It merely determines the default linear size of the image when printed, but this can in any case be overridden by most print programs and so is of no consequence.

John

David W. Jones

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May 13, 2014, 2:43:44 PM5/13/14
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On 05/12/2014 09:23 PM, Marius Loots wrote:
> Hallo,
>
> Tuesday, May 13, 2014, 8:55:04 AM, you wrote:
>>> How can I tell Hugin (or its processor program) NOT to change the
>>> resolution down to 150dpi and rather keep it at 300dpi?
>
> Terry> In the Stitcher tab, try selecting "Calculate Optimal Size", and see if
> Terry> that helps.
>
> In my experience, both the above as well as in
> Preferences - Assistant Tab - Downscale final pano = 100% of final
> width.

That downscale final pano setting annoyed the heck out of me until I
changed the prefernce.

I've never seen Hugin change DPI settings, though. Size, yes, but not DPI.

--
David W. Jones
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Terry Duell

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May 13, 2014, 6:47:41 PM5/13/14
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Hello David,

On Wed, 14 May 2014 04:43:44 +1000, David W. Jones <gnome...@gmail.com>
wrote:

>
> I've never seen Hugin change DPI settings, though. Size, yes, but not
> DPI.
>

That's because the image size is a fundamental property of the image, dpi
isn't.
dpi only relates to the size of the displayed or printed image, hence dpi
is variable and is a property of the way the image is displayed or printed.
If you have an image 300x300 pix, and print or display it at 1x1 inch, it
is shown at 300 dpi.
You can then display or print the image at 2x2 inches and it is 150 dpi
but the basic image hasn't changed.
So, Hugin only deals with image size in pixels.

David W. Jones

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May 14, 2014, 4:01:21 AM5/14/14
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I knew that, but I don't think the original poster did.

Андрей Йердна

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Dec 22, 2017, 8:18:41 AM12/22/17
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Hugin team: can you please disable 70% downscale in options??

Always forget about it :( Annoying

вторник, 13 мая 2014 г., 7:57:53 UTC+3 пользователь tda...@gmail.com написал:

Abrimaal

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Dec 23, 2017, 9:24:52 AM12/23/17
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Do it only once and forever. In File / Preferences / Assistant /
Downscale final pano [ 100 ] percent of the max width.
The panoramas will never downsized again (until you don't want to).

Андрей

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Dec 24, 2017, 11:37:23 AM12/24/17
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I install Hugin occasionally in random PCs )
And I always forget about this option :( It takes some time to remember what happening

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Matt Huszagh

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Aug 14, 2022, 10:27:28 AMAug 14
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I don't entirely agree with this. While all the original pixels in the image may remain, it can be useful for the image to remember it's own size. I use hugin to stitch together large electrical schematics from scans (which it does an incredible job of!) and I like to know the actual size of the page. I'd prefer that the image remembered this information rather than me needing to.

Fortunately, the resolution seems to be pretty simple. Imagemagick will change the reported image density (see this answer). And if you look at the imagemagick documentation it just changes this one attribute, it doesn't change any pixels (i.e., it basically performs the inverse of what hugin is doing here).

The command would be something like:

convert -units PixelsPerInch my_original_image.tif -density 300 my_new_image.tif

Matt

Paloma Canedo

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Oct 6, 2022, 7:14:18 AMOct 6
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Hi!
I use Hugin to create 12 gore spheres to print and sew, using a template posted on this GC (gores.pto). It works very well, the only problem is the quality/resolution loss... Because sometimes I need to print it on 5m spheres...
Can someone help me with this?

Thank you,
Paloma Perrone
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