Evaltex

EvaLTex (Evaluating Text Localization) is a unified evaluation framework used to measure the performance of text detection and text segmentation algorithms. It takes as input text robjects represented either by rectangle coordinates or by irregular masks. The output consists of a complex set of scores, at local and global levels, and a visual representation of the behavior of the analysed algorithm.

Input format

The framework takes as input .txt files containing the coordinates of the bounding boxes surrounding the text objects and binary images corresponding to the text object masks.

Ground truth (GT)

The GT files contains the reference to which the detection and segmentation results will be compared to. For text detection tasks using bounding boxes, a .txt file is enough. If the text objects are represented by irregular masks, then an additional labeled image will be needed.

Text detection

The GT format contains the following attributes:

• img name
  
• image height, image width
  
• text object

• ID: unique text object ID
• region ID: region ID to which the object belongs to
• "transcription": can be empty
• text reject: option that decides if a text object should be counted or not; can be set to f (default) or t (not take into account)
• x: x coordinate of the bounding box
• y: y coordinate of the bounding box
• width: width of the bounding box
• height:x height of the bounding box

e.g.:

img_1

960,1280

1,1,"Tiredness",f,38,43,882,172

2,2,"kills",f,275,264,390,186

3,3,"A",f,0,699,77,131

4,3,"short",f,128,705,355,134

5,3,"break",f,542,710,396,131

6,4,"could",f,87,884,370,137

7,4,"save",f,517,919,314,105

8,5,"your",f,166,1095,302,136

9,5,"life",f,530,1069,213,137

Text segmentation

To evaluate text segmentation we use, in addition to the .txt file a labeled image (each character is labeled differently). Each GT object is represented by a character. Character-level GT objects cannot be grouped into regions and consequently each text object has a different region tag. The x, y, width and height will define the coordinates of the bounding box of each character. e.g.

img_1
960,1280
1,1,"",f,384,43,101,166
2,2,"",f,142,44,46,164
3,3,"",f,38,47,106,163
4,4,"",f,192,80,71,126
5,5,"",f,269,80,100,131
6,6,"",f,501,81,97,126
7,7,"",f,721,81,97,131

Mask representation

In addition to bounding boxes, text objects can also be represented using masks. EvaLTex takes as input binary images (white corresponds to text). TODO add images

Output

The output consists in a local valuation (for each image), as well as a global evaluation (one XML file for a whole database).

TODO add local XML file and global XML file

Performance measurements

Local evaluation

For each matched GT object we assign two quality measures: Coverage (Cov) and Accuracy (Acc);

• Cov computes the rate of the matched area with respect to the GT object area
• Acc computes the rate of the matched area with respect to the detection area

Recall

The Recall ($R$) computes the amount of detected text. We compute 3 measures: a global $R$, a quantitative $R$ that measures the amount detected objects (regardless of the matched area) and a qualitative $R$ that corresponds to the rate of the detected text area with respect to the number of true positives ($TP$).

• $R_{G}={\frac {\sum Cov}{G}}$
• $R_{quant}={\frac {TP}{G}}$
• $R_{qual}={\frac {\sum Cov}{TP}}$

Precision

The Precision ($P$) computes the rate of detections that have a match in the GT. Similarly to $R$, we compute 3 measures: a quantitative $P$ that measures the amount of valid detections (regardless of the matched area) and a qualitative $P$ that corresponds to the rate of the detected text area with respect to the number of total detections, computed as the sum of $TP$ and $FP$

• $P_{G}={\frac {\sum Acc}{TP+FP}}$
• $P_{quant}={\frac {TP}{TP+FP}}$
• $P_{qual}={\frac {\sum Acc}{TP+FP}}$

How to compute the measurements

Parameters to run the tool