Leonardo wrote:
> Does anyone have an idea

Everyone in your class except you ?

An RLE encoded image (bit or byte) stream does clearly say, what color 
(index) the next pixels have (it is not lossy). You pass the strean, 
except that you modify the color (index) of A to B and ob B to A and let 
C D, E... as they were.

Think about the main application of millions of FPGAs, decipher Internet 
streams, unpack base64, decode zip, analyze the content and if certain 
key words are detected modify the information so that for instance an 
HTML page does not display hate speech against the government but keeps 
you in your filtered bubble that your country is the greatest in the 
world.

Your professor tries to show you exactly this, so that you know where 
fake news are coming from.

Thank you  MaWin for the explanation .

Swapping randomly two indexes would be ok but how could we identify two 
colors?
For example I want to identify the green color and swap it or blend it 
with the blue color ? How could that be possible ?

Hi Lothar .
Thank you for the great explanation.
I got your point . Theoretically it's easy to understand .

We have a 4bitmap image . I checked the Bitmap file format in Wikepedia 
and it turns out that a 4 bitmap is identified by BI_RLE4 (which is Run 
length encoding)  It would have been atleast easier if it was 24bitmap 
image (RGB)

>Is this just for simulation with a file as input and output?
Yes

>What additional information did your professor give you?
Literally nothing . We have to learn everything by ourselves this 
semester . He said that it's a challenge for us during this coronavirus 
situation to learn this topic alone .

The problem right now is how to identify the colors ? Is there like for 
each color a defined 4 bit value ?

Leonardo wrote:

> We have a 4bitmap image . I checked the Bitmap file format in Wikepedia
> and it turns out that a 4 bitmap is identified by BI_RLE4 (which is Run
> length encoding)  It would have been atleast easier if it was 24bitmap
> image (RGB)

OK, this is the Microsoft bitmap format. The first thing you have to 
understand is, that this special subformat is an indiced format. That 
means, the content of the bitmap are not color values, but indices into 
a color table.

> The problem right now is how to identify the colors ?

You've to look into the color table. What else?

c-hater wrote:
> You've to look into the color table

Or not.
The excercise only calls to swap 2 colors, not which ones.

MaWin wrote
> The excercise only calls to swap 2 colors, not which ones.

Actually I want to swap 2 specified colors not any two colors .


So can I use this color table as a source ?

It says: Blue is =  0001
         Green is = 0010
         Red is =   0100

Fernando .S wrote:

> Actually I want to swap 2 specified colors not any two colors .

MaWin appearently misunderstood the intention (might be: wanted to 
misunderstand to expose your stupid, incomplete specs)...

> So can I use this color table as a source ?
>
> It says: Blue is =  0001
>          Green is = 0010
>          Red is =   0100

Yes. Exactly this is the sense of a color table. Save memory. Store 4 
bits only in the bitmap instead of 24 (or 32).

Thank you @ c-hater : One last thing to ask :
How do I get the width and the height of a bmp image using VHDL ?
I don't want to write constant values .

Like getWidth() and getHeight() in C for example

Leonardo wrote:
> Thank you @ c-hater : One last thing to ask :
> How do I get the width and the height of a bmp image using VHDL ?
> I don't want to write constant values .

You've to extract it from the bitmap info header of course. Even you've 
to extract the existence(!) of a color table and the color table 
itselves, as long it exists in the file...

Keep in mind: the color table isn't mandatory. In the case of it's 
absence you've to use a "default" (VGA).

That's for very historical reasons...

In the case of existence you've at least to check the number of entries. 
It should be sufficient to cover all appearing indices in the bitmap 
by standard. But you shouldn't trust foreign data at any time...

Leonardo wrote:
> How do I get the width and the height of a bmp image using VHDL

There ist no need to know width and height if all you have to do is swap 
2 colors.

MaWin wrote:

> There ist no need to know width and height if all you have to do is swap
> 2 colors.

Of course he must know this. At least under the given precondition of an 
RLE-encoded bitmap...

Are you stoned or are you not the actual MaWin? I assume the latter...

c-hater wrote:

> Of course he must know this. At least under the given precondition of an
> RLE-encoded bitmap...

I know but still I'm totally new to image processing thus every details 
will count .I have a small knowledge on VHDL so this will be a challenge 
for me .

I actually code most of the time with C and C++ and I'm familiar with 
solving problems .

Logically speaking if I want to have this kind of matrix in my image in 
C/C++
2 red 5 green 8 blue
3 red 5 green 7 blue
4 red 5 green 6 blue
5 red 5 green 5 blue
6 red 5 green 4 blue

I would read everyline at once and then analyze their colors and swap 
the two colors that I want to swap  .(In this case I won't need the 
image_width and height like you said)

In C for example it will be something like this (but still I don't know 
if it works on bmp image )

Char Zeile[101]= {'\0'};;
FILE *Datei = fopen("image.bmp", "r"); //Read modus
 while (fscanf(Datei, " %101[^\n]", Zeile) == 1)
{
 // Analyse the file and swap the colors of this line
 or I make a whole matrix with this file and then swap later ..
}

Something like that : it will read everyline of the bitmap image till 
the end of file (EOF).

Should I follow the same logic on VHDL ?
If yes then I would really appreciate it if you write me some code in 
VHDL how to scanline the image till the EOF.

Two swap two colors in an indexed image you just have to swap the 
correpsonding entries in the color map - there's no need to process the 
image pixels at all.

foobar wrote:
> Two swap two colors in an indexed image you just have to swap the
> correpsonding entries in the color map - there's no need to process the
> image pixels at all.

Could you please write me a little example with vhdl how can you swap 2 
entries colors WITH RLE . It would help me a lot to understand how it's 
working exactly.

First: Parsing BMP-Files in VHDL sounds kind of silly - are you sure you 
got your task right?

Second: As I said, no need to parse the RLE, just swap two entries in 
the palette.

Third: It's your job - you'd learn nothing if I'd do it for you.

Fourth: I would implement a simple CPU (like J1) and write a program for 
it ;-)

foobar wrote:
> First: Parsing BMP-Files in VHDL sounds kind of silly - are you
> sure you
> got your task right?

True It would've been so much better for me if it was in C/C++

foobar wrote:
> Third: It's your job - you'd learn nothing if I'd do it for you.

I didn't ask for you to write the whole code for me . I just wanted a 
little example to know how it works ..

> I actually code most of the time with C and C++ and I'm familiar with
> solving problems .

Then solve it in C/C++ first.  That way you don't have to deal with two 
problems, the algorithm and the new language.  When the C version is 
done, you have the algorithm and know what to do and can now concentrate 
on how to do it in VHDL.  Use a method that can be used in both 
languages, i.e. a state machine.

c-hater wrote:
> Of course he must know this.

You obviously do not know, how the color change is going to work.

foobar wrote:
> Two swap two colors in an indexed image you just have to swap the
> correpsonding entries in the color map - there's no need to process the
> image pixels at all.

That's a clever way.

Lothar M. wrote:

> 2. Take a HEX Editor
> 3. Open  YOUR specific picture file
> 4. Locate the color table in YOUR specific picture file
> 5. Find the two colors in the color table
> 6. Swap their values
> 7. Save the edited file
> 6. Check the result with a picture viewer
> 7. Finally, when the result is what you wanted, then think about how you
> could use VHDL file commands to automize steps 2..7 and write the code



Thank you so much Lothar I'm getting so close to the solution .
I'm trying to use the ASCII codes of the colors right now but there's a 
little problem that I will have at the end .

With my HEX EDITTOR I wanted to set the red to blue without swapping 
them, just replacing and that's all .

But it seems that the red color will change differently : Red color 
became black . I think that it mixed the red with blue color => Black .

Any solutions for that ?

It worked thank you very much Lothar , can you please delete the 
highlighted code that I sent . Maybe some students from my class can see 
the answer .

Leonardo J. wrote:
> Should the red color normally be FF 00 00 (00)  and not 00 00 FF (00)
It depends on definition: RGB vs. BGR

Duke