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Reef mapping

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#1 MaxGhent


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Posted 17 February 2015 - 05:19 AM



For my class project, I went diving and took pictures of a reef  (ca 100m²), and now I have to stitch these photos together.
This is simple in Photoshop when all pictures are taken at the exact same height and angle, but due to underwater currents the pictures are not taken at the exact same height/angle. 
I found software to stitch photos to each other by recognizing several points, but this didnt work with my photos because there were fish on the pics and those fish were in different places at different times..
Anyone who can help, or give usefull links to software/tutorial videos?

Thanks a lot!

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#2 Chris Cosgrove

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Posted 27 February 2015 - 07:35 PM

Oh dear, this sounds like quite a lot of work coming up !


If all these photos had been taken, as you say, at the same range and angle then all the points would have been at the same scale assuming you hadn't zoomed the camera between images.


Photoshop is a raster graphics package which means you cannot grab a corner and scale an image as you could in a vector graphics package, you have to do it using 'Image size'. Presumably all your images are the same size in terms of pixcels x pixcels but the distance between two points on the edge of one is not the same as the distance between the same two points on the edge of its neighbour in pixcels.


What you are going to have to do - unless someone comes up with a better idea - is use 'image size' to change the size of the larger image to the same size as the smaller.


To put some numbers on this. Assuming you have two points on the left hand edge of one photo which you can recognise on the right hand edge of its neighbour, and let us say that in one photo these two points are 1500 pixcels apart and in the other 1800, then, if you reduce the size of the larger in the ratio of 6:5 then the points in both will be 1500 pixcels apart and the images should fit together.


The normal default is 'Maintain aspect ratio'. If your camera angle between shots changed you may find that changing the vertical and horizontal scales by different amounts will adjust for this as well.


In general, reducing the size of an image gives a better result than increasing it although the image size function works in both directions.


I wish you luck !


Chris Cosgrove

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