![]() The specific performance of the above problems can be realized through the following code: #include What is memory alignment? For details, please refer to the article: Alignment of structure members in memory when opening a file with fopen to get the file handle and read the corresponding data, there is a problem that the structure memory is aligned, which will cause errors in subsequent data reading. You can see by comparing the structure and file data:Ġ-1: 0x4d42='BM ', indicating that this is a bitmap format supported by WindowsĪ-D: 0x00000436 = 1078, indicating that 1078 bytes need to be offset from the file header to the bitmap data In VScode, BMP image data can be viewed in binary form by installing the hexdump plug-in. UINT16 bfReserved2 // Reserved, must be set to 0 (8-9 bytes)ĭWORD bfOffBits // Offset from file header to pixel data (10-13 bytes) UINT16 bfReserved1 // Reserved, must be set to 0 (6-7 bytes) UINT16 bfType // 19778 must be a BM string, the corresponding hexadecimal is 0x4d42 and the decimal is 19778, otherwise it is not a bmp format fileĭWORD bfSize // File size in bytes (2-5 bytes) The structure of bitmap header file is defined as follows: typedef struct tagBITMAPFILEHEADER Therefore, the storage order of data 0x1756 in memory is: In hexadecimal, a number occupies 4 bits, so each byte can store 2 hexadecimal digits. Before analyzing the image data, it should be emphasized that in the BMP file, the data storage mode is small endian, that is, assuming that a data needs multiple bytes to represent, the order of data storage bytes is "low address stores status data, high address stores high-level data". In this paper, the file format of BMP image is analyzed according to the above figure. Data segment nameĬorresponding Windows structure definition The data structures of the first three parts are introduced below. The above different parts have different data structures. At this time, the color table is the mapping table between the index and its corresponding color (that is, find the corresponding pixel information by combining the index value with the color table) Color table: use the index to represent the image.It is characterized by rich image information because it is hardly compressed, but it also occupies a large disk space. Thanks a lot For Your Time.According to Baidu Encyclopedia BMP We know that BMP is the abbreviation of Bitmap and the standard image file format in the Windows operating system. įollowing image show us how my msg is hidden in the image This using the famous program 'Paint Shop Pro' ,there is something called 'Split to HSL' ,you will find a new image created called saturation. Hey now one might ask if there is a way to know if this pic hold a msg inside it or not ? Well I found indeed one method ,I discovered it by chance but it can be used only for a black or a white image. Now see the following the picture can you see any difference between two pictures These samples pictures are in the demo and with the source in the release folder. When you are going to try my demo ,you will find three pictures ,use them with the program using the password 'aaaaa' (take care it is CASE SENSTIVE) and read my msg to you then vote for my work. Well since it is just one bit change in each byte so our eye never be able to see the such difference.Saving the result back to the bmp file.Then adding to it 1 or not depending on the srcBin array. ![]()
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