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Read Bitmap Color depth 4 Bits
von Guest (Guest)

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I have a BMP file that I need to read in VHDL, but I have problems 
reading the colors, to be precise, with a color depth of 4 bits.
With a color depth of 24 bits it looks like this:

    r_in : in std_logic_vector(7 downto 0);
    g_in : in std_logic_vector(7 downto 0);
    b_in : in std_logic_vector(7 downto 0);

8 bits each for RGB.

With a color depth of 4 bits, it had to be different on the outside.

I am thankful for every help.

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Re: Read Bitmap Color depth 4 Bits
von Lothar M. (Company: Titel) (lkmiller) (Moderator)

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Guest wrote:
> I have a BMP file
Attach it here, so it can be examined with a simple hex editor.

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Re: Read Bitmap Color depth 4 Bits
von Guest (Guest)

Attached files:
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Lothar M. wrote:
> Gast schrieb:
>  > Ich habe eine BMP-Datei.
> Hänge sie hier an, damit sie mit einem einfachen Hex-Editor untersucht
> werden kann.

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Re: Read Bitmap Color depth 4 Bits
von FpGaNoTfALlSeElSoRgE (Guest)

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What a silly assignment ... poor students.

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Re: Read Bitmap Color depth 4 Bits
von Duke Scarring (Guest)

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Guest wrote:
> With a color depth of 4 bits
4 bit for every color or 4 bits for all together?

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Re: Read Bitmap Color depth 4 Bits
von Guest (Guest)

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With a color depth of 4 bits, i.e. 4 bits per pixel.
With 4 bits the colors are indexed, so there are 16 color entries that 
are used.
This leaves 1 byte for RGB each.

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Re: Read Bitmap Color depth 4 Bits
von Lothar M. (Company: Titel) (lkmiller) (Moderator)

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The first part of this kinda stupid exercise is fairly easy: examine the 
structure of the bmp file to find out what index green and blue have and 
where the picture data starts, then open it, read it, replace the 
corresponding nibbles and write it to a new file.

To find and afterwards fill random rectangles is not that easy, 
especially when they may be rotated in any way.

: Edited by Moderator
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