Signal Processing - November 2017 - 113

Global Visual
Vector

Caption

CNN

a baby holding a toothbrush
in its mouth

RNN
baby
mouth
...
holding
Semantic Tags

FIGURE 6. An illustration of integrate explicit semantic-concept-detection in an encoder-decoder framework.

the research of image captioning. More recently, Microsoft
of -captions that were as good or better than human captions.
sponsored the creation of the Common Objects in Context
Overall, Microsoft Research and Google jointly received first
(COCO) data set [51], the largest image captioning data set
prize in the 2015 COCO Image Captioning Challenge. The
available to the public today. The availability of the large-scale
results of two special systems, human and random, are also
data sets significantly prompted research in image captioning
included for reference.
in the last several years.
There are more systems that have been developed since the
In 2015, approximately 15 groups participated in the
2015 COCO competition. However, due to the high cost, human
COCO Captioning Challenge [52]. The entries in the challenge
judging was no longer performed. Instead, the organizers of
are evaluated by human judgment. Five
the COCO benchmark set up an automatic
human judge metrics are listed in Table 1.
evaluation server. The server can receive
Microsoft Research and
the captions generated by a new system and
In the competition, all entries are assess--ed
then evaluate and report the results on the
based on the results from metric 1 (M1) and
Google jointly received
blind test set in automatic metrics. Table
metric 2 (M2).The other metrics have been
first prize in the 2015
3 summarizes the top 24 entries plus the
used as diagnostic and interpretation of the
COCO Image Captioning
human system as of August 2017, ranked by
results. Specifically, in evaluation, each task
Challenge.
SPICE, using 40 references per image [52].
presents a human judge with an image and
Note that these 24 systems outperform the
two captions: one is automatically generhuman system in all automatic metrics except SPICE. Howated, and the other is a human caption. For M1, the judge is
ever, in human judgment, it is likely that the human system still
asked to select which caption better describes the image, or
has a lead, given that in Table 2 there is a huge gap between the
to choose the "same" option when they are of equal quality.
best systems and a human.
For M2, the judge is asked to tell which of the two captions
is generated by a human. If the judge chooses the automatically generated caption, or chooses the "cannot tell" option,
Industrial deployment
it is considered to have passed the Turing test. Table 2 tabuGiven the fast progress in the research community, the induslates the results of the 15 entries in the 2015 COCO Captioning
try -started deploying image captioning services. In March 2016,
Challenge. Among them, the Microsoft Research entry (MSR)
-Microsoft released the first public image captioning application
achieves the best performance on the Turing test metric,
programming interface as a cloud service [53]. To showcase the
while the Google team outperforms others in the percentage
usage of the functionality, it deployed a web application called
CaptionBot (http://CaptionBot.ai) which captions arbitrary pictures users uploaded [33]. The service also supports applications
like Seeing AI, designed for the low-vision community, that narTable 1. Human evaluation metrics in the 2015 COCO
Captioning Challenge.
rate the world around people who are blind or visually impaired
[71]. More recently, Microsoft further deployed the caption serMetric
Comment
vice in its widely used product Office, specifically, Word and
M1
Percentage of captions that are evaluated as better or
PowerPoint, for automatically generating alt-text, i.e., text deequal to human caption.
scriptions of pictures, for accessibility [61]. Facebook released
M2
Percentage of captions that pass the Turing test.
an automatic image captioning tool that provides a list of objects
M3
Average correctness of the captions on a scale from one
and scenes identified in a photo [34]. Meanwhile, although the
to five (incorrect-correct).
service has not yet been deployed publicly, Google open sourced
M4
Average amount of detail of the captions on a scale
its image captioning system for the community [35]. With all of
from one to five (lack of details-very detailed).
these industrial-scale deployment and open-source projects, a
M5
Percentage of captions that are similar to human
massive number of images and user feedback in real-world scedescription.
narios are collected and serve as training data to continuously
IEEE SIGNAL PROCESSING MAGAZINE

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November 2017

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113


http://www.CaptionBot.ai

Table of Contents for the Digital Edition of Signal Processing - November 2017

Signal Processing - November 2017 - Cover1
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Signal Processing - November 2017 - Cover3
Signal Processing - November 2017 - Cover4
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