Pixel Shift Calculation between two very similar images

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NukerDoggie
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Pixel Shift Calculation between two very similar images

Post by NukerDoggie » 2017-07-14T10:46:01-07:00

I have two screen shot images (PNGs) and I want to calculate the max pixel geometric shift between the objects in the images. Both images are identical size and color depth. Some "objects" in the 2nd screen shot are shifted geometrically as compared to the 1st screen shot.

I have used IM to convert both images to grayscale, then did -canny 0x0+1%+3% to perform edge detection, then I changed all white pixels in the 1st screen shot to green1, and then I blended the two images with 50% blending. I get a result image that nicely shows the geometric shift everywhere it occurs, with green lines shadowed by gray lines in these regions.

Now, how can I use IM to scan this result image and tell me the max geometric shift, in pixels, for the image?

Or, is there a better and more efficient way to perform the entire operation and to find the max geometric shift between the two images?

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fmw42
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Re: Pixel Shift Calculation between two very similar images

Post by fmw42 » 2017-07-14T14:50:34-07:00

Please always provide your IM version and platform, since syntax and scripting may differ. Can you post your two edge images to some free hosting service and provide the URLs here?

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Re: Pixel Shift Calculation between two very similar images

Post by NukerDoggie » 2017-07-14T15:35:59-07:00

Hi Fred,

I am using ImageMagick-6.9.3-Q8 on Windows 7.

Here is the blended image:

https://sabercathost.com/4X6e/frame0_blend.png

Here is the baseline image:

https://sabercathost.com/4X6f/frame0_green_1st.png

Here is the 2nd image:

https://sabercathost.com/4X6g/frame0_canny_2nd.png

In the blended image, note the rotated "Hello World" text - it shows some differences in rendering that I expect and wish to quantify.

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Re: Pixel Shift Calculation between two very similar images

Post by NukerDoggie » 2017-07-15T11:49:18-07:00

Sorry for the 60-sec delay when you want to download each image above from SaberCatHost - lots of people elsewhere said this was the best free file hosting site...oh well....should have checked it out first.

I hope this doesn't prevent people from taking a look at the images.

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fmw42
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Re: Pixel Shift Calculation between two very similar images

Post by fmw42 » 2017-07-15T12:01:42-07:00

I have downloaded them -- yes, it was a pain -- but so far no good ideas how to do what you want.

snibgo
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Re: Pixel Shift Calculation between two very similar images

Post by snibgo » 2017-07-15T13:00:11-07:00

After 60 seconds, nothing happened for me. No download, no nothing.
snibgo's IM pages: im.snibgo.com

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fmw42
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Re: Pixel Shift Calculation between two very similar images

Post by fmw42 » 2017-07-15T14:28:08-07:00

snibgo wrote:
2017-07-15T13:00:11-07:00
After 60 seconds, nothing happened for me. No download, no nothing.
You have to wait, then a button appears and you have to click the button. A really annoying web site for downloading, since you have to wait for each image separately even if you ask to download each page. It will wait for one page to finish before timing the next one.

The OP might consider using dropbox.com (and make the images shareable).

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Re: Pixel Shift Calculation between two very similar images

Post by snibgo » 2017-07-15T15:03:29-07:00

I think I had a button, which I pressed, with no luck. It was yesterday, and I forget.

I have enough internet problems (terrible speeds, when it works at all) that I really can't be bothered with web sites that are deliberately slow.
snibgo's IM pages: im.snibgo.com

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Re: Pixel Shift Calculation between two very similar images

Post by NukerDoggie » 2017-07-16T07:41:32-07:00

For calculating the geometric pixel shift, I can do a horizontal scan, and a vertical scan of the image, and count the distances between green and gray pixels. I can average the numbers, or get max variation. That might suit my purposes well enough. I'll need to use a C++ pgm to do that - not a problem.

It gets a little tricky when the object that's being scanned is at a steep angle, like the rotated text. Depending on the angle and whether I'm scanning horizontally or vertically, the pixel count between green and gray pixels might be exaggerated. So I'll have to make the scan smart, by not letting it confuse a green-gray pixel void caused by a vertical shift with one caused by a horizontal shift, and vice-versa. This is mostly an issue when the scan intersects the rotated object at a very oblique angle.

IM has gotten me all the way to the doorstep of what I need.

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Re: Pixel Shift Calculation between two very similar images

Post by NukerDoggie » 2017-07-16T10:41:30-07:00

One prospect for performing the geometric shift analysis I'm interested in:

https://phys.org/news/2017-01-medical-s ... astly.html

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