ReadPixel and PNG issues

BlitzMax Forums/BlitzMax Beginners Area/ReadPixel and PNG issues

Ant	(Posted 2005) [#1]

Hi, I've been looking at ReadPixel functions that can be found here:

http://www.blitzmax.com/Community/posts.php?topic=49893&hl=readpixel

I've found an odd problem though. The code works as it should with most images I load into it - it prints out the RGB value of each pixel and works great. However, if I load an image which is completely white with the first pixel (0,0) as black, it reports that its rgb value is 255,255,255 (white) instead of 0,0,0(black).

I've got a feeling this might be a compression issue - but I've set compression to 0. I'm using irfanview to save the png's BTW. Has anyone encountered this before?

Below is the code I am using. Thanks

Strict

Graphics 800,600,0

Global spline:TImage=Null
Global splineArray:pixel[]
Global colour:Int
Global alpha:Int,red:Int,green:Int,blue:Int



Type pixel
	Field x:Int
	Field y:Int
EndType


spline=LoadImage("image.png")
If not spline Then RuntimeError "Cannot find file."



Local image:TPixmap
image=LockImage(spline)

Print "******************************************"
For Local x=0 To spline.width-1
	For Local y=0 To spline.Height-1
		colour=ReadPixel(image,x,y)
		GetRGB(colour,alpha,red,green,blue)
		If red<255 
			Print "X: "+x+" Y: "+y+" Red:"+red+" Green: "+green+" Blue: "+blue
			WaitKey
		EndIf
		
		
	Next
Next




Function GetRGB(argb:Int,a Var,r Var, g Var, b Var)
	a=(argb Shr 24) & $ff
	r=(argb Shr 16) & $ff
	g=(argb Shr 8) & $ff
	b=argb & $ff       

End Function

tonyg

(Posted 2005) [#2]

I created a PNG in GGales at 128*128 with first pixel black and it works OK.
I took that png into Irfanview and 'save as' with compression 0 and it still worked OK.

Ant	(Posted 2005) [#3]

Confusing.....not sure what to do. I'll try a couple more images. Is GGales shareware?

Ant	(Posted 2005) [#4]

Got it. I wasnt saving the transparent colour which was messing it up.
Thanks for the help.