Keystone does not correct highly distorted perspectives

[PhaseoneUser48829]

Hello
I find Capture One to be the most intuitive and friendly post processing software, However there is still room for improvement.
My understanding of Keystone (the tool with four handles) is that after applying the transformation, the handles should align to a rectangle with horizontal and vertical sides.
This works for minor distortions, e.g. when the plane of the sensor is only off by a small angle from the plane of the rectangular subject being rectified.
When the plane of the sensor is off by a large angle (for instance when photographing a glass framed image in a severely slanted fashion to avoid unwanted reflections, with the intent to rectify the frame in post) Keystone often does not completely rectify the image. In other words, the Keystone handles form a trapeze rather than a rectangle after applying the transformation. This forces the user to use an alternative method such as DxO ViewPoint.
I suggest adding this fix to the wishlist for future versions of Capture One. I do understand that applying severe rectifications to an image may cause a loss of quality in the areas of the images that are highly magnified by the transformation. But it is up to the user to decide whether or not to rectify an image. There is no theoretical reason why severe transformations cannot be calculated. I suspect the algorithm used in Capture Pro's Keystone is faulty because it decomposes the transformation into a rotation and a differential stretching, rather than applying a single matrix transformation.
Since this is about adding a fix to the wishlist, I have two additional suggestions:
Consider turning the Keystone handles into Loupes, locally magnifying the image under them, when they are moved, to facilitate the precise positioning of the handles. This is similar to how DxO ViewPoint works.
Also, consider making it easier to find the corners of the canvas when using the Crop tool. For dark images, one has to hover the mouse around to hunt for the corners of the canvas.
I believe that these fixes and enhancements would be particularly welcome by your users that do interior or architectural photography.
Keep up the good work!

[Ian3]

You express this in terms that imply you think you are making a suggestion to the Phase One developers. This is a user-to-user forum. If you want to make a suggestion to Phase One for enhancement of the app, you can do so by putting an enhancement request into a support case.

Having said that, I agree that there are times when the keystone tools doesn't manage to rescue a highly distorted image. I have found some success for some images by using the horizontal and vertical keystone adjustment sliders in the tool rather than just the guides. it's a bit of trial and error though getting it right. It may be that for images like that it is quicker to take the image to something like Photoshop or Affinity Photo to correct the shape.

Ian

[SFA]

Hello
I find Capture One to be the most intuitive and friendly post processing software, However there is still room for improvement.
My understanding of Keystone (the tool with four handles) is that after applying the transformation, the handles should align to a rectangle with horizontal and vertical sides.
This works for minor distortions, e.g. when the plane of the sensor is only off by a small angle from the plane of the rectangular subject being rectified.
When the plane of the sensor is off by a large angle (for instance when photographing a glass framed image in a severely slanted fashion to avoid unwanted reflections, with the intent to rectify the frame in post) Keystone often does not completely rectify the image. In other words, the Keystone handles form a trapeze rather than a rectangle after applying the transformation. This forces the user to use an alternative method such as DxO ViewPoint.
I suggest adding this fix to the wishlist for future versions of Capture One. I do understand that applying severe rectifications to an image may cause a loss of quality in the areas of the images that are highly magnified by the transformation. But it is up to the user to decide whether or not to rectify an image. There is no theoretical reason why severe transformations cannot be calculated. I suspect the algorithm used in Capture Pro's Keystone is faulty because it decomposes the transformation into a rotation and a differential stretching, rather than applying a single matrix transformation.
Since this is about adding a fix to the wishlist, I have two additional suggestions:
Consider turning the Keystone handles into Loupes, locally magnifying the image under them, when they are moved, to facilitate the precise positioning of the handles. This is similar to how DxO ViewPoint works.
Also, consider making it easier to find the corners of the canvas when using the Crop tool. For dark images, one has to hover the mouse around to hunt for the corners of the canvas.
I believe that these fixes and enhancements would be particularly welcome by your users that do interior or architectural photography.
Keep up the good work!

Firstly this is intended to be a User to User forum and as such is not an official support channel nor an official conduit for sending ideas to the C1 development team.

To do that create a Support Case, indicate in the title that it is an Enhancement Suggestion and enter your proposal. That ways you get an entry in the ideas database that describes exactly what YOU want and not something interpreted by someone else AND it will be managed, we are told, by the development management team and help them to decide, based on the number of similar requests, where development resource could best be employed to advance the product.

Meanwhile are you aware that the Keystone Tool is set, by default, to correct by 80% (100) not 100%? I'm not sure this would be good for your extreme correction use. However there is a slider in the full tool that allows you to increase the adjustment over the 80% mark (120).

Your Loupe suggestion is interesting but in the meantime are you familiar with the options to navigate quickly around a zoomed in image? Not quite as much potential for elegance as your suggestion but at least an available option.

For the crop tool suggestion it occurred to me that there are some options in the Preferences for personalising how the crop is displayed - mask shades, opacity, etc. and option to display a frame. You have not mentioned them in your description so I could not tell if you thought they were inadequate or simply not relevant to what you are seeking but they seem to relate in some ways for what you have suggested.

Finally - if your need is for business purposes and this sort of sever trapezoidal correction is a daily requirement it may be worth checking whether there are already extended facilities in the Cultural Heritage (CH) version of C1. I have no idea but it occurs to me that CH might have some advanced versions of such features that would probably only be suitable for experienced users.


HTH.


Grant


ETA: I see Ian3 has also responded with some points whilst I was typing this.

[Ian3]

My experience shows that if you are using the combined horizontal and vertical adjustment, Capture One uses 100%. But also, you have to be extremely precise in getting the selection points exactly in the corners of the rectangular object for it to come out right. For more extreme cases it usually takes quite a few tries, and even then it's not easy to get it right. Some other app is often the easier answer.

Ian

[NNN636360000345043571]

I am artist, painter , and want to correct perspective on photos of my painting. It is not higly distorted but the program is not working good at all. After spending money on Phase one , now I have to buy DxO ViewPoint, that program is working perfectly. Shame that crew from Phase one did not react and made poatch to correct Keystone ( four handle) precision.

[Ian3]

I think that the point about precision is that the user has to position the four handles very precisely. In my experience it can be quite tricky.

Ian

[SFA]

I am artist, painter , and want to correct perspective on photos of my painting. It is not higly distorted but the program is not working good at all. After spending money on Phase one , now I have to buy DxO ViewPoint, that program is working perfectly. Shame that crew from Phase one did not react and made poatch to correct Keystone ( four handle) precision.

If you want to be certain of a response you need to direct your question (as a question not a statement would work best) to the Capture One team using a Support Case. In that way it should be managed internally and you will have a Case reference number to refer to during the discussion.

In the meantime, are you using a lens with lens corrections and have you considered trying to correct the problem you have using a tilt and shift lens system?

Is there a way you can take the images you require of of the paintings but avoid the keystone problems in the first place?

Are you using the standard version of Capture One of the Cultural Heritage version?


Grant