Īn additional size uncertainty is introduced by the optional presence of the 12 or 16 bytes needed for the extra bit masks stored immediately after the BITMAPINFOHEADER DIB header and the variable-size GAP depicted in Diag.1 Pixel array (bitmap data) This total file size formula is only an approximation, since the size of the color palette will be bytes for the OS/2 DIB header version BITMAPCOREHEADER, and some files may define only the number of colors needed by the image, potentially fewer than. In the formulas above, the number 54 is the combined size of the 14 byte bitmap file header and the 40 byte popular WindowsDIB header – the BITMAPINFOHEADER (some other DIB header versions will be larger or smaller than that as described by the table above) and the expression is the size of the color palette in bytes. 16bpp images (or higher), may omit the palette part from the size calculation, as follows: , Only images with 8 or fewer bits per pixel must account for the palette. The total bitmap image file size can be approximated as: ,īPP ≤ 8 ( because for pixels larger than 8 bits, the The absolute value is necessary because ImageHeight can be negative The total amount of bytes necessary to store an array of pixels in an n bits per pixel (bpp) image, with 2 n colors, can be calculated by accounting for the effect of rounding up the size of each row to a multiple of a 4 bytes, as follows: ImageHeight is expressed in pixels. The total number of bytes necessary to store one row of pixels can be calculated as: ImageWidth is expressed in pixels. ![]() Mandatory for color depths 1, multiple padded rows are stored consecutively, forming a Pixel Array. To define colors used by the bitmap image data (Pixel Array) Present only in case the DIB Header is the BITMAPINFOHEADER Immediately follows the Bitmap File Header To store detailed information about the bitmap image and define the pixel format Not needed after the file is loaded in memory To store general information about the Bitmap Image File Referring to the diagram 1, the bitmap file is composed of structures in the following order: Structure Name 1 – The structure of the bitmap image file Many different versions of some of these structures can appear in the file, due to the long evolution of this file format.ĭiag. The bitmap image file consists of fixed-size structures (headers) as well as variable-size structures appearing in a predetermined sequence. Also, not all fields are used a value of 0 will be found in these unused fields. Some applications create bitmap image files which are not compliant with the current Microsoft documentation. The following sections discuss the data stored in the BMP file or DIB in detail. A DIB is normally transported in metafiles (usually using the StretchDIBits() function), BMP files, and the Clipboard (CF_DIB data format). A DIB is an external format, in contrast to a device-dependent bitmap, which appears in the system as a bitmap object (created by an application.). The main purpose of DIBs is to allow bitmaps to be moved from one device to another (hence, the device-independent part of the name). ![]() According to Microsoft support: Ī device-independent bitmap (DIB) is a format used to define device-independent bitmaps in various color resolutions. They called these device-independent bitmaps or DIBs, and the file format for them is called DIB file format or BMP image file format. Microsoft has defined a particular representation of color bitmaps of different color depths, as an aid to exchanging bitmaps between devices and applications with a variety of internal representations. Device-independent bitmaps and the BMP file format
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