As information tags

2D bar codes can easily be accessed by taking a picture or scanning. They possess the advantages of large data capacity

high decoding reliability

and wide range of encoding. Therefore

they are widely used worldwide due to the growth of the Internet in recent years. The quick response (QR) code is a 2D bar code. Compared with other 2D bar codes

the QR code has more features

such as high reading speed

large data density

and small occupied space. The QR code can encode arbitrary text strings

emails

hyperlinks

phone numbers

and so on. To obtain the embedded messages

mobile devices are used to capture the QR code

and information is acquired through a QR code reader. Given the popularity of smartphones

the QR code has become the most widespread 2D bar code. A common use of the QR code is to encode URLs so that people can scan a QR code to load a website on a cell phone instead of typing in a URL. QR codes are encoded using Reed Solomon error-correcting codes. Therefore

a QR scanner does not have to view every pixel correctly to decode the content. Error correction corrupts a part of the code (less than the maximum amount that the algorithm can fix) to make an image. This high fault tolerance makes QR codes popular and widely used in many commercial applications. In the conventional QR code

the modules are designated on an image by black and white square patterns

which can easily be identified by machines. However

noisy black and white patterns reveal no intuitive information about the QR code when viewers look at the patterns without the aid of a scanning software; the patterns also seriously degrade the aesthetic appeal of the carrier. Although the aesthetics and visual significance of the code are unimportant for scanning purposes

they do matter in advertising layout and can provide valuable brand distinction. Considering that QR codes often occupy a non-negligible display area in print media

the demand for visually appealing QR codes is increasing. Visually appealing codes incorporate high-level visual features

such as colors

letters

illustrations

or logos. Researchers have attempted to endow the QR code with aesthetic elements

and QR code beautification has been formulated as an optimization problem that minimizes visual perception distortion subject to an acceptable decoding rate. However

the visual quality of the QR code generated by existing methods still requires improvement. The key challenge is the lack of proper understanding or analytical formulations capturing the stability of QR codes under variations in lighting

camera specifications

and even perturbations to the QR codes. Patented and ill-documented algorithms employed to read QR codes cause further difficulties. Consequently

existing approaches are mostly ad hoc and often favor readability at the cost of reduced visual quality. This work presents an algorithm that visually encodes a QR code by synthesizing the conventional QR code with a theme image. This task is fulfilled by dividing the theme image into equal-sized non-overlapping blocks and modifying the average luminance of each block to its corresponding module type in the QR code by applying the well-designed Gaussian modulating function. In the Gaussian modulating function

standard deviation is dynamically determined according to the smoothness of the corresponding module block. The brightness of the central region of the modified module gradually changes along the circular and presents a smooth appearance and different sizes

which make it consistent with the human visual system. In addition

the size of the module's brightness-sensing region can be adjusted according to application scenarios and the sensitivity of the human eye to different noises. In the experimental stage

visually meaningful QR codes are synthesized by setting different parameters

and their correct decoding rate is tested. The optimal parameters are determined to ensure decoding reliability and make the QR code easily recognizable for humans. Furthermore

the correct decoding rate is tested using different mobile devices and decoding applications. Experimental results show that even when the performance of a mobile device is poor

the correct decoding rate remains satisfactory. Compared with a similar method of synthesizing visual QR codes in literature

the proposed method exhibits good performance in terms of the visual quality of the generated visual QR code and the response time in accessing the QR code content. The proposed method generates a visual QR code without referring to the encoding process of the QR code. The algorithm automatically generates a colorful QR code as long an image

data

and parameters are provided. The generated code is superior to the traditional black-and-white QR code and more attractive to users because of its satisfactory identification rate. The algorithm meets the QR code standard

is compatible with any decoding system

can be integrated into corporate identification system

and can be used in marketing

advertising

and other related areas. Applying our experimental results to advertising and industrial design would highlight the recognition of individual and corporate brands and overcome the drawbacks of QR codes with a black and white appearance. The proposed method exerts a positive advertising effect and enhances the willingness of users to scan.