How do I keep a rectangular image as a rectangle in the output?

[Ken Shirriff]

I'm stitching together microscope photos taken on an X-Y stage. However, the images end up slightly distorted because Hugin treats everything as spherical rather than rectilinear. I use an equirectangular projection to position the images planarly, which helps. However, images end up slightly trapezoidal as the pitch increases, which I don't want. I thought the equirectangular lens would fix this, but changing the lens type seems to make no difference. (Maybe I'm using the lenses wrong?)

I'm using a small FOV (1 degree) for the images, but I'm still getting enough distortion to cause difficulty. Is there a way to make Hugin keep a rectangular source image as a rectangle in the output?

I'm sure I'm mangling the terminology here, but hopefully this question makes sense. 

Thank you,

Ken

[Bruno Postle]

Hi Ken, yes you need to use rectilinear for both the unit and output projection, this will preserve straight lines - Bruno

[dkloi]

You may want to look into mosaic mode e.g.

https://hugin.sourceforge.io/docs/manual/Stitching_a_photo-mosaic.html

https://hugin.sourceforge.io/tutorials/Mosaic-mode/en.shtml

The images are treated as lying on a plane, not a sphere. You should be able to translate and the rotate the virtual camera to get the desired framing, tilt, and shift with respect the placement of the image on them plane.

[Ken Shirriff]

Awesome, mosaic mode (TrX, TrY) with rectilinear lenses and projection does what I want. One question: what are the units for TrX and TrY? By experimentation, 1º is approximately 0.0175 for TrX/TrY. But I assume there's some geometrical interpretation.

[Ken Shirriff]

It looks like TrX and TrY are in radians?

[Bruno Postle]

The translation parameters are linear distances. Imagine that the photos are each being projected onto a wall by portable slide projectors, and you are viewing this wall from a distance of one unit. The coordinates for each projector are trx try trz (you are at 0,0,0) - Bruno

On Sun, 16 Nov 2025, 18:32 Ken Shirriff wrote:

It looks like TrX and TrY are in radians?

On Sunday, November 16, 2025 at 10:07:05 AM UTC-8 Ken Shirriff wrote:

Awesome, mosaic mode (TrX, TrY) with rectilinear lenses and projection does what I want. One question: what are the units for TrX and TrY? By experimentation, 1º is approximately 0.0175 for TrX/TrY. But I assume there's some geometrical interpretation.

Bruno

[Ken Shirriff]

Thanks! One (hopefully) final question: how do I center a mosaic image? If I try to center it in Panorama Preview, the pitch and yaw get set, causing the image to be tilted rather than shifted. What I want is the translation parameters to get changed to move the center of the image.

Ken

[Luís Henrique Camargo Quiroz]

    Hi Ken!

    

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Luis Henrique Camargo Quiroz

http://panoramaslh.net/ - http://luishcq.br.tripod.com

[Luís Henrique Camargo Quiroz]

    Hi Ken!

    Glad there is only one question now - or none at all.

    With a "regular' panorama it makes sense to choose an adequate center for the image, say, pointing North or to some interesting feature in the image. However, panning the panorama in a viewer (standalone or through an internet page) you could see anywhere you want.

    For your rectangular image, a mosaic of microscope photos, how will you see or present it to others? Using an image editor like Gimp, or maybe OpenSeadragon to show (efficiently) a very high resolution image in an internet page? In both cases the image will be presented centered in the window, scaled for best fit. The center will ever be the center of the image (or viewing window), and you could pan and zoom without difficulty. There is no need to define a center for your image! 

    Hope this makes sense, 

    Luís Henrique

Em seg., 17 de nov. de 2025 às 15:36, Ken Shirriff <ken.sh...@gmail.com> escreveu:

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[Bruno Postle]

Hi Ken, in the Fast Preview window > Move/Drag tab, there is a
'mosaic' Drag mode that will let you drag the mosaic around the canvas
without tilting it or adding distortion - Bruno

On Mon, 17 Nov 2025 at 18:36, Ken Shirriff wrote:
>
> Thanks! One (hopefully) final question: how do I center a mosaic image? If I try to center it in Panorama Preview, the pitch and yaw get set, causing the image to be tilted rather than shifted. What I want is the translation parameters to get changed to move the center of the image.

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Bruno

[Ken Shirriff]

Thanks! That feature is exactly what I was looking for. I should take a closer look at Fast Preview, since it seems to have a lot of interesting functions.

Ken