How to print BMP photo file in assembly graphics mode

Question

So i tried copying the code to print a bmp file from my learning book at school, did everything as mentioned, and it just displays the error message. Can anyone help me debugging?

CODE:

IDEAL
MODEL small
STACK 100h
DATASEG
;================================
filename db 'test.bmp',0

filehandle dw ?

Header db 54 dup (0)

Palette db 256*4 dup (0)

ScrLine db 320 dup (0)

ErrorMsg db 'Error', 13, 10,'$'
;================================
CODESEG
;================================
proc OpenFile

    ; Open file

    mov ah, 3Dh
    xor al, al
    mov dx, offset filename
    int 21h

    jc openerror
    mov [filehandle], ax
    ret

    openerror:
    mov dx, offset ErrorMsg
    mov ah, 9h
    int 21h
    ret
endp OpenFile
proc ReadHeader

    ; Read BMP file header, 54 bytes

    mov ah,3fh
    mov bx, [filehandle]
    mov cx,54
    mov dx,offset Header
    int 21h
    ret
    endp ReadHeader
    proc ReadPalette

    ; Read BMP file color palette, 256 colors * 4 bytes (400h)

    mov ah,3fh
    mov cx,400h
    mov dx,offset Palette
    int 21h
    ret
endp ReadPalette
proc CopyPal

    ; Copy the colors palette to the video memory
    ; The number of the first color should be sent to port 3C8h
    ; The palette is sent to port 3C9h

    mov si,offset Palette
    mov cx,256
    mov dx,3C8h
    mov al,0

    ; Copy starting color to port 3C8h

    out dx,al

    ; Copy palette itself to port 3C9h

    inc dx
    PalLoop:

    ; Note: Colors in a BMP file are saved as BGR values rather than RGB.

    mov al,[si+2] ; Get red value.
    shr al,2 ; Max. is 255, but video palette maximal

    ; value is 63. Therefore dividing by 4.

    out dx,al ; Send it.
    mov al,[si+1] ; Get green value.
    shr al,2
    out dx,al ; Send it.
    mov al,[si] ; Get blue value.
    shr al,2
    out dx,al ; Send it.
    add si,4 ; Point to next color.

    ; (There is a null chr. after every color.)

    loop PalLoop
    ret
endp CopyPal

proc CopyBitmap

    ; BMP graphics are saved upside-down.
    ; Read the graphic line by line (200 lines in VGA format),
    ; displaying the lines from bottom to top.

    mov ax, 0A000h
    mov es, ax
    mov cx,200
    PrintBMPLoop:
    push cx

    ; di = cx*320, point to the correct screen line

    mov di,cx
    shl cx,6
    shl di,8
    add di,cx

    ; Read one line

    mov ah,3fh
    mov cx,320
    mov dx,offset ScrLine
    int 21h

    ; Copy one line into video memory

    cld 

    ; Clear direction flag, for movsb

    mov cx,320
    mov si,offset ScrLine
    rep movsb 

    ; Copy line to the screen
    ;rep movsb is same as the following code:
    ;mov es:di, ds:si
    ;inc si
    ;inc di
    ;dec cx
    ;loop until cx=0

    pop cx
    loop PrintBMPLoop
    ret
endp CopyBitmap
;================================
start:
mov ax, @data
mov ds, ax
;================================

    ; Graphic mode
    mov ax, 13h
    int 10h

    ; Process BMP file
    call OpenFile
    call ReadHeader
    call ReadPalette
    call CopyPal
    call CopyBitmap

    ; Wait for key press
    mov ah,1

    int 21h
    ; Back to text mode
    mov ah, 0
    mov al, 2
    int 10h
;================================
exit:
    mov ax, 4c00h
    int 21h
    END start

This is all the code.

Answer 1

You need an appropriate .bmp file:

Name: test.bmp
Location: In the current directory
Width: 320
Height: 200
Colors: 256

Take this (Copyright by me! Free for all use!):

Right Click on the picture and save the picture. Reformat it to BMP with a tool like Irfanview and rename it to "test.bmp". Put it in the directory where you start the program.

If you use DOSBox the picture is distorted since DOSBox "translates" the 320*200 video mode Int 10h AH=00h AL=13h to its own screen resolution which is by default a 4/3 mode (I guess 640*480). Changing the value of windowresolution in the dosbox-0.74.conf had no effect here. :-(