Use https://github.com/ImageMagick/ImageMagick/discussions instead.
https://imagemagick.com/discourse-server/
https://imagemagick.com/discourse-server/viewtopic.php?t=18864
Code: Select all
infile="P90achop.jpg"
inname=`convert $infile -format "%t" info:`
rr=`convert $infile -ping -format "%[fx:w*57/90]" info:`
w2=`convert $infile -ping -format "%[fx:w/2]" info:`
h2=`convert $infile -ping -format "%[fx:h/2]" info:`
ww=`convert xc: -format "%[fx:2*$rr*tan(0.5*90/57)]" info:`
hh=`convert xc: -format "%[fx:2*$h2/cos(45/57)]" info:`
ww2=`convert xc: -format "%[fx:$ww/2]" info:`
hh2=`convert xc: -format "%[fx:$hh/2]" info:`
echo "rr=$rr; w2=$w2; h2=$h2 hh=$hh; ww=$ww; ww2=$ww2; hh2=$hh2"
convert -size ${ww}x${hh} xc: $infile -virtual-pixel black -monitor \
-fx "xx=(i-$ww2); aa=atan(xx/$rr); yy=(j-$hh2); v.p{$rr*aa+$w2,yy*cos(aa)+$h2}" +monitor \
${inname}_corrected6.jpganthony wrote:The fact that straight lines are coming out as straight lines is a good indication that the distortion is correct.
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-fx "xx=(i-$ww2+0.5); jj=(j-$hh2+0.5);
aa=atan(ii/$rr);
xx=$rr*aa+$w2; yy=jj*cos(aa);
v.p{xx+$w2-0.5,yy+$h2-0.5}"
The issue is that the fov is not exactly 90 degrees. That is why I had to calculate it from the width of the image in mm and the focal length in mm. Recall that the input image is on a cylinder but unwrapped to be flat. The focal length is the radius of the cylinder. And the arc length formula for the extent of the cylinder is given by s=r*fov where s=width of input image. Thus fov=w/r=90mm/57mm.But these should be able to be calculated from the size of the image itself. That is we know the width of the image is to form a arc of 90 degrees (optional argument), and the pinhole (focal length) is exactly in the center of that arc. Also we have the aspect ratio for the height. so radius=forcal_length=width*2/PI (for a 90 degree arc).
Fred can you give me that calculation?
I was going to script this eventually and would have called it cylinder2rect as it corrects a cylinder distortion to a rectangular form or cylinder2perspective as the rectangular form is a perspective image (i.e. pinhole camera onto a plane). The key argument is the fov. But in the above, I had to compute it from the focal length and image dimension both in physical rather than pixel dimensions.What should the distort be called? Does this type of photo have a specific name?
EG: -distort ??? "90,center_x,center_y"
where 90 is the arc of the film in degrees, and center is optional center of distortion (optional)
A fov=180 would certainly be a problem, but I don't think you need to limit it to fov=90. I believe that one can still do larger fov values before it goes to wild. I would guess even 120 degrees would not be too bad. Recall the height of the output varies as 2/cos(fov/2). SoPS: it is posible to get an infinite image with a x-center set to an edge of a 90 degree arc, so a limit of 45 degree from that center in output may be wise (unless a user viewport is specified).
I believe after looking at that the page that it is not describing the same kind of transformation. It is describing a sphere projected onto an cylinder which is then unwrapped. (A mercator-like mapping transformation). We are doing a partial cylinder projection onto a perspective plane.that makes it harder for handling other cylindrical images such as the 360 degree one on the Hugin page
http://hugin.sourceforge.net/docs/manua ... ction.html
Actually the specs on the reference page say it is nearly 90 degree field of view and give a specific focal length of 57. So one has to believe what they say and not infer too much. The f stop is well defined and so is the focal length which is related to it. So I would tend to believe that rather than assuming that the fov is truly 90 degrees.I would not be surprised it may be that it is actually engineered to be 90 degrees, but with 57mm being a near approximation (for advertising). We would need to know for certain!
No the image on that page is not a sphere in a mercator-like (world map) projection. If it was the top and bottom of the image will all be a single color.fmw42 wrote:I believe after looking at that the page that it is not describing the same kind of transformation. It is describing a sphere projected onto an cylinder which is then unwrapped. (A mercator-like mapping transformation). We are doing a partial cylinder projection onto a perspective plane.that makes it harder for handling other cylindrical images such as the 360 degree one on the Hugin page
http://hugin.sourceforge.net/docs/manua ... ction.html
Fair enough. But it will still probably be provided as required user input argument of 90.467Actually the specs on the reference page say it is nearly 90 degree field of view and give a specific focal length of 57. So one has to believe what they say and not infer too much. The f stop is well defined and so is the focal length which is related to it. So I would tend to believe that rather than assuming that the fov is truly 90 degrees.
Sorry, I thought you were worried about the height which as I described above varies as 2/cos(fov/2).anthony wrote:
Of course any cylinder (or sphere) to plane distortion mapping would produce an infinite 'flat' image when angle from center of distortion reaches 90 degrees, as at that point the view becomes parellel to the flat plane! (limit of the tan() function). As such using the hugin cylinder image, you would only be able to convert a small part of the image. It could however be used to generate a set of four 'cube face' images
I would probably include some angle limit to the output of any cylinder/sphere to rectangular. Anything more than 60 degree from center is probably getting ridiculous. Such a limit is not needed for the reverse, as you could never input an infinite plane image.
So we may need to include arc limits as some of the optional arguments that need to be worked out! (unless the user inputs a 'viewport' image that will bypass the need for limits). And I need to know before I start implementing as it is harder to add them later!