Read the Header of bitmap
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Tina
am 11 Nov. 2021
Bearbeitet: Walter Roberson
am 11 Nov. 2021
Hi can anyone guide me how to open a bitmap or bmp file header ? I have opened in hex editor but I need to open it by using matlab ?please guide
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Walter Roberson
am 11 Nov. 2021
Bearbeitet: Walter Roberson
am 11 Nov. 2021
I am saying that if you were reading from a real bmp file then using fread with '*uint8' would give you back numeric values. You could display them in decimal if you want.
But the snapshot you posted is not a real bmp file: it is part of a hexadecimal dump of a bmp file. You need to decide which kind of file you need to process.
Consider the numeric value denoted by the word sixty-six. That is an abstract value that exists by itself independent of representation. It can be represented in multiple ways. One of the ways is 66, which is the character 6 followed by the character 6. Another way is 01000010 which is character 0 followed by character 1 then several character 0 and so on. Another way is 42 which is the character 4 followed by the character 2.
But in computer languages the character 0 is not the same as the numeric value zero. The character 0 is represented by the numeric value forty-eight, the character 1 is represented by the numeric value forty-nine and so on.
A real BMP file starts with a byte with numeric value sixty-six. Which happens to be also be the numeric value used to encode the character B (this was deliberate.)
But the file you posted a snapshot of... it starts with numeric value thirty-nine. Which is the same as the numeric value used to encode apostrophe. And then your file has numeric value forty-eight. Which is the encoding of the character 0, not the numeric value zero.
Someone has taken a binary file and converted it to characters that represent the hexadecimal form.
Consider that the numeric value one hundred and twenty three can be stored in a single byte: you could store it in a file that is a single byte. Or you could store it in a file as the sequence of characters 1 2 3 (which would be numeric values forty-nine fifty fifty-one inside the file) which would be a file of length three bytes. Or you could store it as the sequence of characters 7 B which would be numeric values fifty-five sixty-six in the file, a file of length two bytes. And the file you showed us would not use the single numeric value one hundred and twenty three: it would use the characters 7B (well, 7b really but I do not have the character code for b memorized. Ninety-eight I think it would be)
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yanqi liu
am 11 Nov. 2021
clc; clear all; close all;
bmp = fopen('common_demos.bmp','rb');
type = fread(bmp,2,'char')
bmpsize = fread(bmp,1,'long')
bfReserved1and2 = fread(bmp,1,'long')
bfOffBits = fread(bmp,1,'long')
biSize = fread(bmp,1,'long')
biWidth = fread(bmp,1,'long')
biHeight = fread(bmp,1,'long')
biPlanes = fread(bmp,1,'short')
biBitCount = fread(bmp,1,'short')
biCompression = fread(bmp,1,'long')
biSizeImage = fread(bmp,1,'long')
biXPelsPerMeter = fread(bmp,1,'long')
biYPelsPerMeter = fread(bmp,1,'long')
biClrUsed = fread(bmp,1,'long')
biClrImportant = fread(bmp,1,'long')
fclose(bmp);
3 Kommentare
Walter Roberson
am 11 Nov. 2021
'rb' is not documented. The 'b' will be ignored. Using 'r' is equivalent.
People mistakenly think they need to use 'rb' because in C you would use 'rb' for binary and 'r' for text files. In MATLAB it is 'r' for binary, and 'rt' for text files.
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