Load and display bitmap file using Fread

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Tina 2021-11-13

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评论： Tina 2021-11-14

Bmp files have header usually of 54 bytes.How can i get rid of it to display my bmp by using fread.i tried by following code.but the image i get has disorted color.How can i get rid of header and reshape in a way that color dont get disturbed

fid=fopen("m.bmp",'rb')
f=fread(fid,'uint8')
a=reshape(f,512,512,3)

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Answer 1

Walter Roberson 2021-11-14

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编辑：Walter Roberson 2021-11-14

http://www.ece.ualberta.ca/~elliott/ee552/studentAppNotes/2003_w/misc/bmp_file_format/bmp_file_format.htm

Pixel Data

an array of bytes that defines the bitmap bits. These are the actual image data, represented by consecutive rows, or "scan lines," of the bitmap. Each scan line consists of consecutive bytes representing the pixels in the scan line, in left-to-right order. The system maps pixels beginning with the bottom scan line of the rectangular region and ending with the top scan line.

[...]

RGB values are stored backwards i.e. BGR.

(I interpret this as meaning that you have the B, G, R for the left-bottom pixel, then the B, G, R for the one to the right of that, and so on, then the B, G, R for the second-from the bottom left pixel, and so on. Eventually the end of the file would be B, G, R for the top right corner.)

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Tina 2021-11-14

Thankyou

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Answer 2

Rik 2021-11-13

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You should reshape the data, not the fid. To remove the first 54 bytes you can use fseek, or just skip it from your array:

fid=fopen("m.bmp",'rb');
f=fread(fid,'uint8');
fclose(fid);
a=reshape(f(55:end),512,512,3);

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Tina 2021-11-13

I tried doing this but the image I get had all of the color are scattered . When I compared it with imread() .the arrangements of value inside the variable were very different.