A method to generate color palettes from images is proposed. Here, deep neural networks (DNN) are utilized in order to consider human perception. Two aspects of human perception are considered; one is attention to image, and the other is human preference for colors. This method first extracts N regions with dominant color categories from the image considering human attention. Here, N is the number of colors in a color palette. Then, the representative color is obtained from each region considering the human preference for color. Two deep neural-net systems are adopted here, one is for estimating the image area which attracts human attention, and the other is for estimating human preferable colors from image regions to obtain representative colors. The former is trained with target images obtained by an eye tracker, and the latter is trained with dataset of color selection by human. Objective and subjective evaluation is performed to show high performance of the proposed system compared with conventional methods.

Embedding efficiency is an important issue in steganography methods. Matrix embedding (1, n, h) steganography was proposed by Crandall to achieve high embedding efficiency for palette images. This paper proposes a steganography method based on multilayer matrix embedding for palette images. First, a parity assignment is provided to increase the image quality. Then, a multilayer matrix embedding (k, 1, n, h) is presented to achieve high embedding efficiency and capacity. Without modifying the color palette, hk secret bits can be embedded into n pixels by changing at most k pixels. Under the same capacity, the embedding efficiency of the proposed method is compared with that of pixel-based steganography methods. The comparison indicates that the proposed method has higher embedding efficiency than pixel-based steganography methods. The experimental results also suggest that the proposed method provides higher image quality than some existing methods under the same embedding efficiency and capacity.

Image authentication is applied to protect the integrity of the digital image. Conventional image authentication mechanisms, however, are unfit for the palette-based color images. Palette-based color images such as GIF images are commonly used for media communications. This article proposes a palette-based color image authentication mechanism. This novel scheme can guarantee the essentials of general authentication schemes to protect palette-based color images. Morphological operations are adopted to draw out the tampered area precisely. According to the experimental results, the images embedded with the authentication data still can preserve high image quality; specifically, the new scheme is highly sensitive to altered areas.

Conventional authentication methods, proposed mainly for gray-scale and color images, are not appropriate for palette images, which usually contain simple contents with a limited number of colors. In this paper, a new approach is proposed to verify the integrity of palette images and to locate tampered regions without re-quantization and re-indexing processes. The proposed approach is based on a combined use of both the fragile watermarking and the digital signature approaches, taking the advantages of both approaches and avoiding their drawbacks. To protect a block of an image, authentication signals are first generated according to a secret key. Based on an embeddability property defined in the study, the pixels of each block are classified as embeddable or non-embeddable. Only the former ones are used to embed the authentication signals. A corresponding digital signature is generated as well to compensate the possibly limited embedding capacity of the embeddable pixels that are insufficient in number. To authenticate a block, the recovered authentication signals, yielded from the extracted watermark and the received digital signature, are compared with the one generated according to the correct secret key, to prove the block's legitimacy. The effectiveness and the security of the proposed method are analyzed and tested with a variety of palette images. The results indicate that the proposed method can offer high authentication accuracy as well as maintain a good tradeoff between the authentication signal portability and the resulting image quality.

In previous work we have proposed a steganographic technique for gray scale images called BPCS-Steganography. We also apply this technique to full color images by decomposing the image into its three color component images and treating each as a gray scale image. This paper proposes a method to apply BPCS-Steganography to palette-based images. In palette-based images, the image data can be decomposed into color component images similar to those of full color images. We can then embed into one or more of the color component images. However, even if only one of the color component images is used for embedding, the number of colors in the palette after embedding can be over the maximum number allowed. In order to represent the image data in palette-based format, color quantization is therefore needed. We cannot change the pixel values of the color component image that contains the embedded information, but can only change the pixel values of the other color component images. We assume that the degrading of the color component2 image with information embedded is smaller than that of the color component images that are used for color reduction. We therefore embed secret information into the G component image, because the human visual system is more sensitive to changes the luminance of a color, and G has the largest contribution to luminance of the three color components. In order to reduce the number of colors, the R and B component images are then changed in a way that minimizes the square error.

This paper proposes a dual port color palette SRAM using a single bit line cell. Since the single bit line cell consists of fewer bit lines and transistors than standard dual port cells, it is able to reduce the area. However, the cell has had a problem in writing a high level. The port swap architecture solves the problem without any special mechanism such as a boot strap. In the architecture, each of two bit lines is assigned to the read/write MPU port and the read only pixel port, respectively. When writing a low level, the MPU port uses pre-assigned bit line. On the other hand, when writing a high level, the MPU port uses the bit line assigned to the pixel port by a swap operation. During the swapping, the pixel port continues the read operation by using the bit line assigned to the MPU port. A color palette using this architecture is fabricated with a 0. 5 µm CMOS process technology. The memory cell size reduces by up to 43% compared with standard dual port cells. The color palette is able to supply the pixel data at 300 MHz at the supply voltage of 3.3 V. This speed is enough to support the practical highest resolution monitors in the world.