When starting OCR for a new file we need to setup a few things, which requires you to start the OCR process too see what happens. The three most important things are:
If the font size is small (letter height less than ~28 pixels), you should use "Tesseract 5" or "Binary image compare".
You can double click on a line in the list view to start the "Inspect window" where you can see how letters will be split, recognized and their sizes.
"Number of pixels is space" will determine how words will be found, so "h o w a r e y o u" indicates a too low value, and "howareyou" indicates a too high value. For a normal Blu-ray .sup file 8-15 pixels of space between words are common, 10-12 for most.
If the subtitle contains italic, then do find one of these lines, right-click on the image and choose "Set italic angle". Italic angle will mostly be used to help split words (together with "Number of pixels is space").
When running the OCR you should have "Draw missing texts" checked - otherwise you will get a "*" for unknown letters.
Clicking on the Start OCR button will start the OCR process and with my chosen .sup file I get the following prompt pretty fast:
Here I must enter the new letter in "Character(s) as text" but I also need to make sure that the green and red lines are correct.
For characters like "i" and "!" make sure that the dot has some green and also make sure that a red line separate the letter parts.
In the image below I've entered "j" as text and added a extra red line between the white blocks hoping that it will avoid recognizing wrong letters like "l".
Now I just click "OK" and the OCR process continues.
After running through a few lines I can see that some letters are detected incorrectly. In the "Unknown words" list it looks like "y" is detected as "V". So I press the "Stop" button which stops the OCR process.
I double-click on line #6 in the list view, which start the "Inspect window". Here I click on "Add better match".
In the "nOCR character window" I enter "y" as text and press "OK".
Then I continue the OCR process from line #6.
I add few more chars like "j" earlier, and then I notice the entry "ridicu1ous" with "one" instead of "L" (line #67) in the "unknown word" list.
I double click on line #67 in the list view to inspect again.
The "1" (one) actually looks like "l" (L), so I delete the character from the OCR db by clicking on the "Delete" button.
Then I continue from line #67 and the error is gone.