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remove keystoning from painting photos - Printable Version

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remove keystoning from painting photos - broker12 - 07-11-2017

I would like to know if GIMP has this feature . . . in photo shop, it' is called removing keystoning from photos of paintings. That's not a genuine name. It's how others talk about this feature.

What removing keystoning does is allow you to straighten up the edges off a photo of a painting. Usually, it is quite difficult to set up a painting so that the photo of it is perfectly square. In photoshop, this is the procedure for removing/straightening the edges of the photo of the painting:

Removing keystoning from a photographed rectangular work is not difficult in Photoshop. Use the Crop tool to get within a quarter inch of your painting, (but not too close). With the NAVIGATOR, ZOOM IN to at least 100%, or much more. Now SELECT/SELECT ALL. Go to EDIT/TRANSFORM/DISTORT. You will find in the corners, 4 small box buttons. Drag each of these out one at a time until you get each corner of your painting pulled tight to the corners of the image file frame. Press ENTER or RETURN (Mac), to accept these changes. Any perspective distortion present in the original image will be corrected now.

To get the proportions or aspect ratio of your painting back on track, take measurements of your original painting, go to IMAGE/IMAGE SIZE, disable the CONSTRAIN PROPORTIONS checkbox, so you can alter them. Now type into the height and width dimension boxes, the actual measurements of your painting. Since this may increase your file size to something overwhelming, you can reduce the pixels per inch to something much smaller than 300dpi to something like 96 dpi, or 72 dpi. Press OK, and your painting will be flat, square, true proportioned, and looking good! Remember to go back and reset the CONSTRAIN PROPORTIONS checkbox in IMAGE SIZE, for the next time you use that function

If anyone knows how to do this in GIMP, please let me know . . . Thanks


RE: remove keystoning from painting photos - rich2005 - 07-11-2017

Gimp has a perspective deform tool.

To retain the original proportions, if you know them, set up some horizontal and vertical guides.
Select the perspective deform tool, click in the canvas.

[Image: FJtbktN.jpg]

Drag the handles, the squares at the corners, to suit

[Image: NzKwRWi.jpg]

Click transform it to fix it, then maybe use the crop tool to size or select, invert selection, to fill in the left over edges

[Image: PkzzF7V.jpg]


RE: remove keystoning from painting photos - Blighty - 07-11-2017

(07-11-2017, 01:19 PM)broker12 Wrote: I would like to know if GIMP has this feature . . . in photo shop, it' is called removing keystoning from photos of paintings. That's not a genuine name. It's how others talk about this feature.

What removing keystoning does is allow you to straighten up the edges off a photo of a painting. Usually, it is quite difficult to set up a painting so that the photo of it is perfectly square. In photoshop, this is the procedure for removing/straightening the edges of the photo of the painting:

1. Use the crop tool to crop unnecessary space around the image.

2. Select the Perspective tool.
Set the mode to Corrective (Backward).
Click on the image.
Drag the 4 corners of the grid onto the corners of the painting.

[attachment=631]

3. Use the Scale feature to restore the original aspect ratio of the painting
From the menu bar, use Image > Scale


RE: remove keystoning from painting photos - broker12 - 07-11-2017

Thanks to you both. I'm on the run just now, but later today, I'll dive in and see if I can sort it out. I ran into the perspective tool several months ago, but had no luck with it . . . I suffer from SLS . . . slow learner syndrome. Again thanks.