Herbi Writer's Letter Evaluation Steps
When a student has written a letter, the Herbi Writer software looks at the letter and declares it as either "correct" or "incorrect". Most of the steps taken during the evaluation process are simple, but have found to be effective for many students' needs. However, the steps are far from perfect, and sometimes Herbi Writer will make the wrong declaration about the letter. Any feedback you have on the evaluation process can help improve it for the future, so please send comments to Barker@Herbi.org.
The four steps for evaluating a letter
Letter evaluation begins when a student as written the same number of ink strokes as those contained in the sample letter. (For example, one stroke for 'a', or two strokes for 't'.) Herbi Writer then performs the four checks listed below, and if the student's letter satisfies all the checks, then it is declared "correct".
Checking letter size
Herbi Writer first checks the size of the "bounding box" of the student's ink strokes compared to that of the sample letter. A "bounding box" is the smallest box around the stroke which contains all of the ink. If the width or height of the student's letter is larger than that of the sample letter, and the difference exceeds a specific distance, then the letter is considered to be incorrect. Also, if the ratio of the width or height of the student's letter relative to that of the sample letter exceeds certain maximum or minimum thresholds, then the letter is considered to be incorrect. (No ratio checks are not done with small ink strokes. For example, the dot of an 'i'.)
This means the letters on the right below would be considered incorrect for the sample shown on the left.
Checking the length of the strokes
Herbi Writer then checks the amount of ink that the student used to write the letter, (that is, the length of the ink stroke.) If the ratio of the length of the student's letter relative to that of the sample letter exceeds certain maximum or minimum thresholds, then the letter is considered to be incorrect.
This means the letter on the right below would be considered incorrect for the sample shown on the left. (This is because the student wrote an extra vertical line after completing the letter.)
Checking how far the strokes strays from the expected path
Herbi Writer then makes a deeper analysis of the letter. It tries to find twenty evenly distributed points along the path of the student's letter, and twenty evenly distributed points along the path of the sample letter. Regardless of how fast or slow the student wrote their letter, the set of points found along the two sets of letters should be similar if the student's letter was drawn out in a similar way to the sample letter. Herbi Writer then compares the points from the student's letter and the sample letter. If the distance between where the sample letter's points and the student's letter's points exceeds a certain threshold, then the letter is considered incorrect.
This means the letter on the right below would be considered incorrect for the sample shown on the left, because the letter the right has a different starting point than that of the sample letter.
Checking where the stroke goes relative to the start of the letter
Herbi Writer then uses the sets of points built up in the previous check, to see if the direction of the points relative to the start of the letter is the same as that for the points in the sample letter. This helps to detect some incorrect letters not detected by the earlier checks.
Beginner, Intermediate, or Advanced?
There are various thresholds for distances and ratios used in the four evaluation steps. Different users needs different threshold values. So Herbi Writer has three levels of evaluation to choose from; Beginner, Intermediate, or Advanced. The "Beginner" level uses larger distances and ratios, to allow the student's letter to stray further form the sample letter while still being evaluated as "correct". These distances and ratios are reduced at the "Intermediate" and "Advanced" levels, meaning that the student's letter has to be more similar to the sample letter before it is considered "correct".
To set the appropriate level for your students, click the "Settings" button followed by the "Evaluation" tab in the Settings window that appears. Then select the level from the list of levels that appears at the top of the window, as shown in the following image.
Customizing the evaluation process, (for advanced users)
You may find that one of the evaluation rules described above does not work well for your students. In some cases it may turn out that with some adjustments to the distance and ratio thresholds, the evaluation process might be more useful. If you'd like to try adjusting the evaluation thresholds, click the "Settings" button following by the "Customize" tab. The following button will be shown in the window:
If you click the "Tune evaluation settings..." button, the following window will appear:
You can then adjust the distances and ratios are during the evaluation process, for the three levels of Beginner, Intermediate, and Advanced. It is difficult to predict what effect changing some of these threshold values will have when used with you student's handwriting, so it may be best to try adjusting the numbers and then writing some letters to see what the effect has been.
You can always restore the default settings to remove any adjustments you have made, by clicking the "Restore defaults" button.
Viewing technical details, (for advanced users)
For people interested in the technical details when letters are evaluated, you can check the "Show technical results of evaluation in the Herbi Writer window" check box in the above window, and click OK. When you do that, the following items appear in the bottom left of the window:
These items can be removed by unchecking the "Show technical results of evaluation in the Herbi Writer window" check box that was previously checked.
When technical details are being shown, details about the evaluation are shown after the four evaluation steps have been taken. As part of this, the twenty evaluation points along the sample letter and student letter are shown. The points along the student's letter are shown in red, and the points along the sample letter are shown in blue, (but in the student letter's area to make comparison easier as you look at them.) The following image shows two sets of points displayed:
Some details are also shown beneath the letter. The last line of the details will always say "Correct" or "Incorrect" based on the results of the four evaluation steps. So if the evaluation is "Incorrect", you can look at the other details to determine which attributes of the student's letter crossed the evaluation threshold. For example, maybe the letter was too wide, or the stroke was too long, or the letter strayed too much from the expected path.
Note: The details are rather brief and complicated at the moment. In time the details will be expanded to make it easier to understand the technical results of the evaluation.
Examples
The following image shows a letter being considered incorrect because the difference between its width and the width of the sample letter was greater than the Beginner threshold of 32 pixels. Similarly, for the height of the letter is too large.
The following image shows a letter being considered incorrect because the ratio of its size to the size of the sample letter was less than the Advanced threshold of 75%.
The following image shows a letter being considered incorrect because the ratio of its length to the length of the sample letter was greater than the Advanced threshold of 125%. (This is because the student wrote an extra vertical line after completing the letter.)
The following image shows a letter being considered incorrect because a point along the path of the student's letter had strayed too far from its expected path at the Advanced level. This is because the student has drawn out the letter in a way that was different to the sample letter. (The points that were compared and found to be too different are shown in different colours in the image.)
You can clear the technical details and can continue writing by pressing the "Continue with next letter" button.
Hopefully the above details can help you get the most from the Herbi Writer software. Any feedback is always welcome. If you'd like more information please contact Barker@Herbi.org.