Trouble finding matches for images

--- Preview colors
the colors with that matches are shown correspond to the color bar below the similarity slider:
- reddish: similarity high >0.85
- pinkish: similarity medium: around 0.7
- other colors: low <0.6

--- image quality
see: http://sikulix-2014.readthedocs.io/en/latest/basicinfo.html#sikulix-how-does-it-find-images-on-the-screen
images should always be found with a score above 0.8 - 0.9.
images that get a lower score bare the risk to not be found or even create false positives.

--- Preview difference to score at runtime
When running the script, similarity scores are rounded to 2 decimals.
Preview internally uses findAll() and handles the score fully as float values without rounding.
This may lead to inconsistencies as you have.

--- suggestions

1. recapture your image, so it has as little background towards the edges and concentrates on the key aspects. This should give you a similarity score beyond 0.8 - 0.9.

2. IDE feature "Show": in the top bar of the IDE there is a button "Show", that works so:
- put the cursor somewhere in the line with the image/pattern
- take care that the image is visible on the screen
- click the button
- the image should be found and highlighted (if not: nothing happens, null is written in the message area)
For just checking this is slightly better than Preview, because it internally uses the find feature.
I will revise this feature to be more verbose.

When I first capture the images from the GUI, SikuliX finds them with a similarity value of 99%.
Then after a few passes, the situation described may occur. I recaptured the images multiple times. Sometimes it helped for a while, but then the error came back.
Capturing a larger portion of the image works for a few, but other images can not have a larger capture area because the region around them is subject to change which would definitely result in a FindFailed.
It is probably worth noting that I have this issue exclusively when at least one of the image dimensions is rather small in the order of 20-30 pixels. But as I said, I can not capture larger images for all of them.

since generally the captured image are fix and do not change, there must happen some changes on the screen in the area, where you think your capture should be found.

The smaller the images the fewer changing pixels may lead to this effect.

I have to admit, that these situations are hard to debug.

this might be helpful:
if not exists(img):
  saveLastScreenImage()
  exit(1)

where img is the offending image.

You will have a LastScreenImage.png (the screenshot, where in your image was not found) in the folder SikulixStore in the <sikulix appdata> folder (see docs).

all the best

visually compare the image with the

You need some imageviewer, that allows to zoom into an image down to the pixel level (each pixel is shown as a square)

I was able to narrow down the issue a little bit more.
The problem only occurs if the image is not found at the exact same location where I captured it in the first place. Even slightly moving the window that the application is running in by a few pixels on the screen can trigger these events. Then it can also happen for larger images.

Since with SikuliX all is about squares of pixels found on the screen having the same size (width x height) as the captured image, not found situations always are caused by changes to the pixels on the screen.

So analyse the situation on the screen at time of failure as suggested in comment #3.

I have the last screen on the monitor. I can analyze it however I want. OpenCV/Sikulix initially throws a FindFailed. Then when I analyze the screen where the FindFailed occured SikuliX finds the image, but with a lower similarity and marks the region where the image is with purple color instead of red.
Since it is a static image, there is no point in analyzing a screenshot instead of the screen itself.

I cannot see, that you did anything, what I suggested in comments #1 and #3.

If you get a FindFailed, then the image was not found on the screen in that moment.
This moment can only be documented and analysed with a shot according to comment #3.

... Since it is a static image ...
I am sure it is, but the screen is not!

Go back to
http://sikulix-2014.readthedocs.io/en/latest/basicinfo.html#sikulix-how-does-it-find-images-on-the-screen

... and understand how SikuliX works.

BTW: comment #5 is simply wrong.