readpixels dithering problem

Monkey Forums/Monkey Programming/readpixels dithering problem

pyongpyong

(Posted 2013) [#1]

hello!~

This problem appears to be dithering.

So I would like to find a workaround.

Ask for advice.

sorry... little english powered by google translator...

therevills

(Posted 2013) [#2]

Code example and what target?

Gerry Quinn

(Posted 2013) [#3]

I'm guessing Android - it just seems to be a thing with some devices, they have low colour resolution and so they dither. I imagine there is no fix if you want to use ReadPixels with such devices except to use threshold values with the same low colour resolution.

pyongpyong

(Posted 2013) [#4]

target for android
my device is "lg optimus view 2" & "nexus s"
image source = 32bit png file

Function filter_dropShadow:Void(arr:Int[], _shadow1:Int, _shadow2:Int)

        For Local i:Int=0 To arr.Length-1
        Local r : Int = ( arr[i] Shr 16 ) & $ff
        Local g : Int = ( arr[i] Shr 8 ) & $ff
        Local b : Int = arr[i] & $ff
        
        If r=0 And g=0 And b<34
          arr[i] = (_shadow1 Shl 24)+(r Shl 16)+(g Shl 8)+b
        End If
        If r=0 And g<17 And b=0
          arr[i] = (_shadow2 Shl 24)+(r Shl 16)+(g Shl 8)+b
        End If
        
        If r=0 And g=0 And b=0
          arr[i] = 0
        End If
    
        Next i

End Function

Midimaster

(Posted 2013) [#5]

have a look on what Nobuyuki is doing here: http://monkeycoder.co.nz/Community/posts.php?topic=7702

He provides a method to read images before the device could dither them. And it works!

Import mojo
Import opengl.gles11
.....

	Method GrabWithoutDither:Int[](FileName$)
	' from: nDrawExts2, by Nobuyuki (nobu@...). 

               Local data:Int[], info%[2]
  		#If TARGET="android" 
                 Local db:DataBuffer = LoadImageData("monkey://data/" + FileName, info)
                Print "DATA BUFFER LENGTH= " + db.Length        
                Local timeSpent:Int = Millisecs()
                
                'Copy the data buffer into an array.
                 data = data.Resize(db.Length / 4) '32-bits = 4 bytes
        
                'We need to swap bytes of R and B channels around.
                For Local i:Int = 0 Until db.Length Step 4
                        Local j:Int = db.PeekInt(i)
                        
                        data[i / 4] = (j & $ff000000) | ((j & $00ff0000) Shr 16) | (j & $0000ff00) | ((j & $000000ff) Shl 16)
                Next
        
                Print "Operation took " + (Millisecs() -timeSpent) + "ms"
        #Endif        
		Return data
	End

pyongpyong

(Posted 2013) [#6]

to Midimaster
thank you. but i see...
it is different way.
i want not dithering image from 'case by ReadPixels to WritePixels'

Midimaster

(Posted 2013) [#7]

maybe I misunderstood you...

In your first post you wrote that the problem maybe caused by ReadPixels()? And in your second post you talk about an function which works with an array arr:Int[]. I guess this array contains the image datas. If you did create this array before your function with ReadPixels() it is now already damaged.

Nobuyuki's way is a second possibility to create image arrays, but they are not damaged. You could work with an intact image data array...

pyongpyong

(Posted 2013) [#8]

to Midimaster
I know :) Thank you~
But I need to filter the ARGB.
I wonder how the force dithering.
Dithering 'on / off' is a way in monkey...

ElectricBoogaloo

(Posted 2013) [#9]

In general, don't expect Android to be exact with these sorts of things. Dithering and low-colour palettes cause all sorts of issues, and Android Fragmentation makes everything that much worse.
There are ways to request that the system doesn't do dithering, but given the chaos I've already seen, I wouldn't trust that it'll always work as expected.

In short. Don't rely on readpixels. Avoid at all costs, or at the very least, expect it to be wrong most of the time. Unless you're comparing "really dark vs really light", don't attempt to use it.
There's probably other ways to do what you're trying to do.

Sub_Zero

(Posted 2013) [#10]

I wrote a little module to force dithering off on android... Hold on a couple of minutes...

Midimaster

(Posted 2013) [#11]

After grabbing the image in Nobuyuki's way, you can filter the data as you like. It should be no problem...

Do you want to manipulte image, which are avaiable as files? Or do you want to manipulate the current screen of your game?

Dithering On/Off does not work on several devices. We tested this yesterday....

Sub_Zero

(Posted 2013) [#12]

Here you go:

http://www.subsoft.net/downloads/aglv05.zip

Unzip to your module folder and import with

Import agl

Then you can:

Field gl:AGL

'In Oncreate:
gl = New AGL()

'In onrender, run this once:
gl.DisableDithering();

By the way: Midimaster is right, not all devices support this...

Nobuyuki

(Posted 2013) [#13]

@sub_zero

by the way, not related to the topic but related to AGL -- I'm pretty sure the mojo target on Android calls GlDisable(GL_BLEND) automatically whenever you call SetBlend(0). I say that because it was a pain in my behind figuring out why my custom blends weren't working on Android at first; calling SetBlend(1) first made it work because it calls GlEnable(GL_BLEND) :V

pyongpyong

(Posted 2013) [#14]

Thank you many answers.:)

I want to like the picture attached.

i need many pieces of tile.

so can't like a Nobuyuki's source.

I'm Going to find another way if a this idea. OTL

Nobuyuki

(Posted 2013) [#15]

Are you trying to make a drop shadow or a mask of some kind? I can try to help you, but I'm not sure I understand the diagram. It should be possible to do what you want, though.

Edit: I saw your previous post. I'll try to help you later today! After I run some errands...

Sub_Zero

(Posted 2013) [#16]

@Nobuyuki: Yes I know :)

This module wasn't made for release but the DisableDithering() method works :)

Nobuyuki

(Posted 2013) [#17]

@Pyongpyong

Does it still give you dither problems with this? (using nDrawExts2......)

Import mojo
Import nDrawExts2

Function Main:Int()
	New Game()
End Function

Class Game Extends App
	Field img:Image
	Field shad:Image
			
	Field FirstLoad:Bool = True
	
	Method OnCreate()	
		img = LoadImage("test.png")
		
		SetUpdateRate 60
	End Method
	
	Method OnUpdate()
		
			If FirstLoad
				Local size:Int[2]
				Local data:Int[] = PixelArray.Get("test.png", size)				
				Print data.Length()
				'Let's load the image using the data array.
				shad = CreateImage(size[0], size[1])
				 filter_dropShadow(data, 4, 4)
				'Write pixels
				shad.WritePixels(data, 0, 0, size[0], size[1])

												
				FirstLoad = False
			End If
			
	End Method
	
	Method OnRender()
			Cls(0, 0, 64)

			'Background stripes
			SetAlpha(0.1)
			For Local i:Int = -32 To DeviceHeight() +32 Step 32
				DrawRect(0, i + (1000 - Millisecs() Mod 1000) * 0.032, DeviceWidth(), 16)
			Next
			SetAlpha(1)
			

			If FirstLoad = False  'Gotta wait for the images to load before trying to blit them.
				'Draw slices
				DrawImage(img, 8, 8)
				If shad <> Null Then DrawImage(shad, MouseX(), MouseY()) Else DrawText("Shad is null", 8, 8)
			End If

	End Method

End Class

Function filter_dropShadow:Void(arr:Int[], _shadow1:Int, _shadow2:Int)

        For Local i:Int=0 To arr.Length-1
        Local r : Int = ( arr[i] Shr 16 ) & $ff
        Local g : Int = ( arr[i] Shr 8 ) & $ff
        Local b : Int = arr[i] & $ff
        
        If r=0 And g=0 And b<34
          arr[i] = (_shadow1 Shl 24)+(r Shl 16)+(g Shl 8)+b
        End If
        If r=0 And g<17 And b=0
          arr[i] = (_shadow2 Shl 24)+(r Shl 16)+(g Shl 8)+b
        End If
        
        If r=0 And g=0 And b=0
          arr[i] = 0
        End If
    
        Next i

End Function

The code above uses your filter_dropshadow() code. I don't know what it does, but you have some strange replacements in there that appear to be for replacing alpha. Here is code that might let you make a drop shadow a different way:

'Summary:  Fills an image entirely with a color, preserving alpha.
Function ColorFill:Void(arr:Int[], r = 0, g = 0, b = 0, opacity:Float = 1)
	Local pixel:Int[]
	For Local i:Int = 0 Until arr.Length
		pixel = PixelArray.GetARGB(arr[i])
		pixel[0] = Int(pixel[0] * opacity)
		pixel[1] = r
		pixel[2] = g
		pixel[3] = b
		arr[i] = PixelArray.ToARGB(pixel[0], pixel[1], pixel[2], pixel[3])
	Next
End Function

Hope this helps~

pyongpyong

(Posted 2014) [#18]

sorry i'm busy

to Sub_Zero
Wow!
I wanted it!
Thank you very much:)

to Nobuyuki
I'm making a picture editor (17x16 tile-based).
Outline of each layer was required to shadow effects.
Each of the tiles to create a single image.
So you can not use.
That's really thoughtful of you.

as a slight token of gratitude:)

Sub_Zero

(Posted 2014) [#19]

pyongpyong: Glad to be of any help :)