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Color to Black and White Converter

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DFrostCreated:
This program will convert color images to black and white in seconds!I will update it soon 
DEF CONVERT X,Y,X2,Y2
FOR I=X TO X2
FOR I2=Y TO Y2
A=GSPOIT(I,I2)
RGBREAD A OUT R,G,B
B=(R+G+B)/3
GPSET I,I2,RGB(B,B,B)
NEXT
NEXT
END
ResourcesCode Snippets
MZ952#1
This only supplements color with the blue color channel. Could it be better to—say—take the average of R,G,B and use that value instead? 
DEF GRAYSCREEN X0,Y1,X1,Y1
VAR X,Y,R,G,B
FOR Y = Y0 TO Y1
 FOR X = X0 TO X1
  RGBREAD GSPOIT(X,Y) OUT R,G,B
  GPSET X,Y,GRAY((R+G+B)/3)
 NEXT
NEXT
END
DEF GRAY(V%)
 RETURN RGB(V%,V%,V%)
END
Yolkai#2
Replying to:MZ952
This only supplements color with the blue color channel. Could it be better to—say—take the average of R,G,B and use that value instead? 
DEF GRAYSCREEN X0,Y1,X1,Y1
VAR X,Y,R,G,B
FOR Y = Y0 TO Y1
 FOR X = X0 TO X1
  RGBREAD GSPOIT(X,Y) OUT R,G,B
  GPSET X,Y,GRAY((R+G+B)/3)
 NEXT
NEXT
END
DEF GRAY(V%)
 RETURN RGB(V%,V%,V%)
END
I thought this as well, but Randomous pointed out that B is in fact reassigned to the average of the three channels before writing. Choosing a different name would have been better though, and it still doesn't take into account the alpha bit.
MZ952#3
Replying to:MZ952
This only supplements color with the blue color channel. Could it be better to—say—take the average of R,G,B and use that value instead? 
DEF GRAYSCREEN X0,Y1,X1,Y1
VAR X,Y,R,G,B
FOR Y = Y0 TO Y1
 FOR X = X0 TO X1
  RGBREAD GSPOIT(X,Y) OUT R,G,B
  GPSET X,Y,GRAY((R+G+B)/3)
 NEXT
NEXT
END
DEF GRAY(V%)
 RETURN RGB(V%,V%,V%)
END
Oh, you're right, I didn't follow the code through correctly. The alpha channel doesn't do anything for the graphics screen unless it's value is 255 (or zero?).
Yolkai#4
Replying to:MZ952
This only supplements color with the blue color channel. Could it be better to—say—take the average of R,G,B and use that value instead? 
DEF GRAYSCREEN X0,Y1,X1,Y1
VAR X,Y,R,G,B
FOR Y = Y0 TO Y1
 FOR X = X0 TO X1
  RGBREAD GSPOIT(X,Y) OUT R,G,B
  GPSET X,Y,GRAY((R+G+B)/3)
 NEXT
NEXT
END
DEF GRAY(V%)
 RETURN RGB(V%,V%,V%)
END
If (for some reason) there is color data stored in the color channels and a value of 0-254 in the alpha channel, this function will set a nonblack pixel for a "transparent" pixel in the source. As suggested to me by 12Me21 in chat, this makes it an inaccurate transform even on the default resources:
12Me21#5
I made a really fast version (takes about 1/3 second for the entire screen), but it requires the sound DLC because it uses ARYOP: 
DEF GRAY X,Y,W,H
 DIM COL%[W*H],RED%[W*H],GRB%[W*H]
 
 'SAVE DATA
 GSAVE X,Y,W,H,COL%,TRUE 'save 16 bit colors
 
 'EXTRACT RED
 ARYOP #AOPDIV,RED%,COL%,&H800
 ARYOP #AOPMAD,COL%,RED%,-&H800,COL%
 
 'EXTRACT GREEN
 ARYOP #AOPDIV,GRB%,COL%,&H40
 ARYOP #AOPMAD,COL%,GRB%,-&H40,COL%
 ARYOP #AOPADD,RED%,RED%,GRB%
 
 'EXTRACT BLUE
 ARYOP #AOPDIV,GRB%,COL%,&H2
 ARYOP #AOPMAD,COL%,GRB%,-&H2,COL%
 ARYOP #AOPADD,RED%,RED%,GRB%
 
 'GET AVERAGE
 ARYOP #AOPDIV,RED%,RED%,3
 
 'MAKE GRAY
 ARYOP #AOPMAD,COL%,RED%,&H2,COL%
 ARYOP #AOPMAD,COL%,RED%,&H40,COL%
 ARYOP #AOPMAD,COL%,RED%,&H800,COL%
 
 'LOAD DATA
 GLOAD X,Y,W,H,COL%,TRUE,TRUE
END
MZ952#6
Replying to:12Me21
I made a really fast version (takes about 1/3 second for the entire screen), but it requires the sound DLC because it uses ARYOP: 
DEF GRAY X,Y,W,H
 DIM COL%[W*H],RED%[W*H],GRB%[W*H]
 
 'SAVE DATA
 GSAVE X,Y,W,H,COL%,TRUE 'save 16 bit colors
 
 'EXTRACT RED
 ARYOP #AOPDIV,RED%,COL%,&H800
 ARYOP #AOPMAD,COL%,RED%,-&H800,COL%
 
 'EXTRACT GREEN
 ARYOP #AOPDIV,GRB%,COL%,&H40
 ARYOP #AOPMAD,COL%,GRB%,-&H40,COL%
 ARYOP #AOPADD,RED%,RED%,GRB%
 
 'EXTRACT BLUE
 ARYOP #AOPDIV,GRB%,COL%,&H2
 ARYOP #AOPMAD,COL%,GRB%,-&H2,COL%
 ARYOP #AOPADD,RED%,RED%,GRB%
 
 'GET AVERAGE
 ARYOP #AOPDIV,RED%,RED%,3
 
 'MAKE GRAY
 ARYOP #AOPMAD,COL%,RED%,&H2,COL%
 ARYOP #AOPMAD,COL%,RED%,&H40,COL%
 ARYOP #AOPMAD,COL%,RED%,&H800,COL%
 
 'LOAD DATA
 GLOAD X,Y,W,H,COL%,TRUE,TRUE
END
Huh. I knew about the RINGCOPY thing, but it didn't quite register with me that the sound processing instructions could be used for anything other than sound processing.
DFrost#7
Here is a slightly faster version(by my predictions) 
DEF CONVERT X,Y,X2,Y2
'get width and height of area to convert----
VAR W=X2-X
VAR H=Y2-Y
'-------------------------------------------
VAR AREA=W*H'calculates area
WHILE COUNT<AREA
VAR X3=(AREA MOD W)+X'gets the single axis value into an x value
VAR Y3=(FLOOR(AREA/WIDTH))+Y'gets the single axis value into a y value
VAR COL=GSPOIT(X3, Y3)
VAR R, G, B
RGBREAD COL OUT R, G, B'convert a single
'value integer into three values
VAR GREY=(R+G+B)/3'or "gray" if you spell it
'that way
GPSET X3, Y3, RGB(GREY, GREY, GREY)'recolor
'that pixel in greyscale
WEND
END