The illusion is that as your field of view is limited, and as your brain assumes the lines are straight you see them as straight.īut with a camera, a lens with a wider field of view than your eye, or some software you can actually see that curvature. The answer is you are seeing a curved line with a smooth transition between. If you look to one side all lines will converge to that side, and if you look to the other side, the lines will converge to the other side.īut how can this be possible if you did not see the lines break at any point? Stand in the middle of the longest hall in your house, or, if it is safe in the middle of a small street. I want to talk about something else.Īll straight lines of the real world must be straight at the image too. I will not discuss in depth any technique, because you have already some good answers. The program runs in Windows and it's portable (=no installation needed) It has more controls than the previous shown in my answer. G'MIC is freeware and it's also available for GIMP.ĪDD2 Freeware image editor PhotoDemon seems to have very good generic lens distortion corrector. There it was G'MIC filter pack's filter Distort Lens with negative distortion. Its generic (=none special type specific) Lens Distortion filter made this:Īgain: Not exact, but maybe even a little better than PTLens's.ĪDD: Quite the same result as in Affinity Photo was available in Krita. PTLens has a free 10 photo trial.Īnother attempt was made in Affinity Photo. I guess it stretches the image horizontally. It's generic fisheye distortion corrector made this: It knows many popular lenses, but it also has some generic filters with wide adjustment ranges. I tried PTLens correction filtering program. I guess you have already thoroughly tested and seen that GIMP's generic lens distortion compensating filter doesn't the job. I guess you haven't the needed lens distortion data nor Photoshop. If you use generic distortion correcting filters you of course do the same - you try to get some straight lines back. Theoretically known straight lines around the image could help clever software to find a good guess of the needed correction, but that's a math problem and I must skip that theory. Photoshop's CameraRaw knows hundreds of cameras and lenses. Then you should have also the lens profile and the aperture and focus settings used in this photo. To correct the lens distortion you should have a program which can do lens distortion profile based corrections. The ancient lensless camera obscura worked and still works that way when the imaging surface is a plane. I see you want to map straight lines to straight lines. To be exact one must also tell what kind of imaging is considered to be right. Somewhere new pixels are interpolated to stretch an area and elsewhere an area can be squeezed to smaller number of pixels. Of course some resolution loss can occur when the image is resampled. it doesn't mix to any point light from several points of undistorted image. I have not found any workarounds for this behavior yet.Theoretically lens distortion can be reversed if the distortion is one to one i.e. Notice that I am toggling the visibility of the layer pointed to by the red arrow, yet only the layers outside the group are affected. Now for the bad news, This also means that When trying to toggle the visibility of many layers Within a layer Group It does not work, only selecting the visibility of the group as a Whole, Notice that the layer within the layer group stays invisible when toggling the other layers with Shift+ Click What this means is that when you make a layer invisible within a group, it will stay invisible when toggling visibility of other layers and groups.īefore toggle and after toggle, I am toggling the visibility of the layer pointed to by the red arrow. Gimp 2.8 will still toggle visible layers using Shift+ Click on the eyeball, but now with layers within Layer Groups Gimp will respect layers that are invisible, or visible within a Group, There is a discussion here by developers - 1 Installed from sudo add-apt-repository ppa:otto-kesselgulasch/gimp Shift+ Click on the eyeball, on the layer you want to remain visible.
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