Thumbnails

[pmcabinet]

OK, I give up. I have searched. Some of my images have a thick, solid (red in my case) bar line across the bottom of the thumbnail, just below the star rating bar. What does this mean?

As a rider to the question, could I suggest that an alphabetical index for the help pages would be very useful to the new user? The 'search help' function returns a list of topics with no clear indication of which topic might cover the term(s). Or have I just misunderstood it?

[Tveloso]

This sounds like you have color-coding active for a Category (or Keyword) assigned to the file:

        https://www.photools.com/help/imatch/cat_basics.htm#?dl=h-34

...and this is displaying in the thumbnail's Category Color Bar:

        https://www.photools.com/help/imatch/fw_basics.htm#a_catcolor

[Mario]

This is the Category Color Bar.

Tip: Did IMatch tell you that you have duplicate files in your collection?
These files are by default added to a category named "DUPLICATES" (if you use the English user interface language for IMatch), which is color-coded in red by default.
So, duplicate files will show a red category color bar.

See  The Category Properties Tab for more info about color-coding for categories and Automatically Marking Duplicate Files for information about automatically marking dupicate files.

There is no alphabetical help index, sorry.
The help as a built-in search function (based on hand-curated keywords and full-text indexing) and you can open the table of contents for the help via the book icon at the top.
Each help page has a table of contents which you can open via the link at the top. With <Ctrl>+<F> you can utilize the browser search function.

Power of Google

It understand that is hard to find something like "I have a red color bar inside the thumbnail panels in the File Window".
Alternatively, you can easily use the power of Google (I do!) to search the IMatch help. When I Google for

color bar site:photools.com

I get (see attachment), which gives some helpful links.

[pmcabinet]

Thank you very much Mario; (and thanks too to Tveloso for your links). I suspected this particular colour bar might relate to duplicates, but I've been nervous of dealing with them until I have a better understanding of what actually defines a 'duplicate'. Many of those categorised as such (a lot by my modest standards) are actually shots taken at slightly different intervals, of a few seconds say (and not, for me, duplicates).
But, if I follow your link and search for 'Copies' instead it produces no results (which is perhaps a bit suspicious because my Pictures folder was a bit of a mess - that's why I invested in your wonderful software).

Anyway, I will get to grips with the Duplicate/Copy distinction and setting my preferences for Indexing and Categories. In the meantime, how might I set the database not to show the the category colour bar for duplicates? I find it distracting at present and don't yet understand the implications residing in the 'Add files to categories' options in Edit>Preferences>Indexing. Can I just uncheck 'DUPLICATES' in the 'Assign copies (...)' options?

You are very patient with us newcomers and I appreciate that hugely!

[Mario]

IMatch differentiates between binary identical images (dupes) and visually identical images, see How do I?... find duplicate files?
You control if and how IMatch looks for duplicate files during import via the corresponding options: Searching for Duplicate Files

If you turn this feature off and remove all files from the DUPLICATES category (Select them with <Ctrl>+<A> and then press <U>), the red color bar will vanish.
You can also disable the color-coding for the DUPLICATES category: The Category Properties Tab or hide the category color bar in your File Window layout via it's options.

That being said, having duplicate files is usually an issue that needs fixing.

Many of those categorised as such (a lot by my modest standards) are actually shots taken at slightly different intervals, of a few seconds say (and not, for me, duplicates).

In that case it seems that the files are so similar (image bit-wise) that they are considered duplicates. I assume if only a small number of pixels change between your images, the algorithm will consider it a dupe.
Switch to binary identical duplicates to avoid this, because this requires a 100% bit-by-bit similarity over the entire file to quality as a duplicate.

[pmcabinet]

I get it! Thank you Mario.