OCR

[lightgoal]

Hello, 

What is a good illumination for reading text from a plastic (a car battery door). the text is printed there by hot metal!. and we have almost 20 different type of doors in color. also each type has different place for text. and another bad part is that there is an attached barcode near text ,we must read (It makes illumination some harder.). The battery doors have as good reflection-ability as a clean glass, only it's not as flat as a flat glass. and the amout of reflection differs for different type of doors. 

 another question is that is it good to have a large character set file or a short size. I mean is this a good idea to make 100 samples of each character or it's better to try to keep it shorter, (there is enough time for process).

thank you

[lightgoal]

I also have some question about refrence character.

what will happen if we don't define a refrence character?

and when we define a refrence character and OCR returns the id score as how close it is to the refrence char, then what will other chars in a class be good for?

thank you

[BruceAmmons]

It sounds your surface is smooth and reflective.  Usually the best light for this sort of application has a low angle of incidence.  The light reflects off the smooth surface and does not enter the camera lens, unless it is the printed area.  In the printed area, light reflects and diffuses and a good amount enters the camera lens.  This gives you white characters on a dark background.

The reference character is just the one that is displayed when you select that character.  It doesn't really do much.  The multiple chars in a class are useful when the character might have a different appearance in different situations.

Bruce

[BCho]

Hey Lightgoal,

Bruce made some good suggestions regarding the lighting of you system and the reference character. If you are seeking some more information, chapter 18 of the NI Vision Concepts Manual discusses the Optical Character Recognition aspect of the NI Vision software.

Hope this helps.

Ben

[lightgoal]

Hi,

I think an angled light is the true idea but untill the hot metal which makes the text on plastic has one effect on every part that is different from the other (I mean every part may receive the hot metal in one presure and this makes that every part has text with one depth that is different from the other.), I don't think a white text on a black bakgrnd be a good choice. especialy when the text has some unpredictable edges because of melt plastic.

[BCho]

Hey Lightgoal-

Just to add another comment to this thread. One of the good things about lighting is you can mess with it a little bit and find the lighting that yields that best results; trial and error if your will. So if you are concerned about shadows because of the varying depth of the text, you could use a smaller angle and see if it yields more consistent results.

Hope this helps.

Ben