Pixel Color

[Walt Decker]

Is there an LB method to obtain the pixel color at point x, y?

[Rod]

No native method. The standard workround uses GetPixel() API function. There are examples posted. But it is SLOW! The other technique is to open the .bmp directly and just access the color quads or triplets. That can be a lot faster. Again there are examples posted.

[Walt Decker]

That is what I thought. I do not see a flood-fill method either. Looks like I will have to float my own for both.

Thank you

PS:

print #handle, "getbmp bmpName x y width height"

Does this mean that the bitmap is loaded into a memory bitmap from a file or that it creates a memory bitmap from the graphic control beginning at X, Y to width, height and gives it the name of bmpName?

[Rod]

Yes the command gets a copy of the screen area named and creates a new graphic in memory. Can be saved with savebmp.

[Rod]

For what it is worth this is file based getpixel / setpixel Can be a lot faster than API if trawling through lots of pixels. My getpixel function is a bit wierd because it fills three globals for Red Green and Blue. It could easily return one long value but Liberty needs three values for most of its color commands. It will trash the image you give it so take care.

WindowWidth  = 700
   WindowHeight = 400
   UpperLeftX   = (DisplayWidth-WindowWidth)/2
   UpperLeftY   = (DisplayHeight-WindowHeight)/2
   graphicbox #1.gb1,10,10,300,300
   graphicbox #1.gb2,330,10,300,300
   open "SET GET Pixel" for graphics_nf_nsb as #1
   #1 "trapclose [quit]"
   global bmpw,bmph,padding,offset,bytes,Blue,Green,Red




   [loadbmp]
       filedialog "Choose an image","*.bmp",file$
       if file$<>"" then
           'display the original bmp in gb1
           loadbmp "original",file$
           #1.gb1 "down ; drawbmp original 0 0"

           'now open the same bmp file for binary read/write access
           open file$ for binary as #bmp

           'analyse the file header bytes
           seek #bmp,10 'picture data offset, where the color data starts 4 bytes of data
           offset=asc(input$(#bmp,1))+asc(input$(#bmp,1))*256+asc(input$(#bmp,1))*65536+asc(input$(#bmp,1))*16777216
           seek #bmp,18 'width 4 bytes of data
           bmpw=asc(input$(#bmp,1))+asc(input$(#bmp,1))*256+asc(input$(#bmp,1))*65536+asc(input$(#bmp,1))*16777216
           seek #bmp,22 'height 4 bytes of data
           bmph=asc(input$(#bmp,1))+asc(input$(#bmp,1))*256+asc(input$(#bmp,1))*65536+asc(input$(#bmp,1))*16777216
           seek #bmp,28 'bits per pixel, ie color depth 2 bytes of data
           bits=asc(input$(#bmp,1))+asc(input$(#bmp,1))*256

           'work out start of picture data and how to move through file
           pointer=offset

           'work out how many bytes in the bits per pixel 24=3 bgr 32=4 abgr
           bytes=bits/8

           'work out padding each raster line must be a 4byte multiple
           mult=bits/8*bmpw/4
           padding = 4*(1-(mult-int(mult))) mod 4
           close #bmp

       end if

   [setall]
       'this demo updates every pixel of the image
       open file$ for binary as #bmp

       for y=1 to bmph
           for x=1 to bmpw

               'run through binary file data moving the file pointer as we go
               seek #bmp, pointer

               'get pixel color stored as BGR Liberty needs RGB
               b=asc(input$(#bmp,1))
               g=asc(input$(#bmp,1))
               r=asc(input$(#bmp,1))

               'change the color
               r=r-150
               if r<0 then r=0

               'set pixel color
               'because we read three bytes we need to set the file pointer back
               seek #bmp, pointer
               #bmp chr$(b);chr$(g);chr$(r);

               'move on
               pointer=pointer+bytes
           next

           'add padding at end of raster line
           pointer=pointer+padding
       next

       'note we need to close the file to have Windows
       'write the last update
       close #bmp
       gosub [show]

   [setpixel]
       'this demo sets individual pixels via function setpixel()
       'open temporary file for read and write access
       open file$ for binary as #bmp
       for n=0 to bmpw-1 'zero index
           null=setpixel(n,n,0,0,0) 'x,y,r,g,b
       next
       close #bmp
       gosub [show]

   [getpixel]
       'this demo retrieves the RBG of a pixel via function getpixel()
       'open temporary file for read and write access
       open file$ for binary as #bmp
       'run along top line
       for n=0 to bmpw-1 'zero index
           null=getpixel(n,0) 'x,y
           'the global RGB variables are filled
           print Red,Green,Blue
       next
       close #bmp

       wait


   [show]
       'show what we did, load file as bmp and display
       loadbmp "newfile",file$
       #1.gb2 "down ; drawbmp newfile 0 0"
       return

   [quit]
       close #1
       end


       function setpixel(x,y,r,g,b)
           'raster lines are stored bottom up so we invert y
           y=(bmph-1)-y
           pointer=offset+x*bytes+y*(bmpw*bytes+padding)
           'set pixel color
           seek #bmp, pointer
           #bmp chr$(b);chr$(g);chr$(r);
       end function

       function getpixel(x,y)
           'raster lines are stored bottom up so we invert y
           y=(bmph-1)-y
           pointer=offset+x*bytes+y*(bmpw*bytes+padding)
           'get pixel color stored as BGR Liberty needs RGB
           seek #bmp, pointer
           Blue=asc(input$(#bmp,1))
           Green=asc(input$(#bmp,1))
           Red=asc(input$(#bmp,1))
       end function


[Walt Decker]

Thank you fellows. Sorry for the late reply. I was involved in a small home remodel for the last few days.

I never work directly from an image file simply because it is faster to load the data into memory and work from there.