'Getting' a image with transparency

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Zeal

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Posted: 12th Apr 2006 14:39

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Im trying to take some snapshots of objects for my imposter billboards, and im not sure how to capture the alpha channel. Sure I could use a color key, but that would give me all or nothing transparency. Is there anyway to capture the alpha channel when using set camera to image?

Thanks in advance

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dark coder

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Posted: 12th Apr 2006 15:13

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currenty i dont think theres any support for this, which is rather annoying, if you make a 2nd camera and draw it to a corner and remove the backdrop, you can get nice alpha`s annoying that you cant use that for billboards :/.

Halowed are the ori.

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Ric

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Posted: 12th Apr 2006 15:38

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You mean snapshots of 3d objects textured with an alpha layer? If so , you could do this (although it's a pretty messy workaround!):

Take a snapshot of your object as normal. Then, load up the textures again into a new image number, convert it to a memblock, and swap the rgb values for the alpha values, in other words creating a greyscale texture of alpha values. Texture the objects with this new image, take a second snapshot. COnvert both snapshots into memblocks and transfer the average rgb value of the second greyscale one to the alpha channel of the first normal one. Told you it was messy!

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Chris Franklin

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Posted: 12th Apr 2006 15:38

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Just an idea not tested it been as dbp is not installed at the moment

Why not make a plain use a black on that then build another plain with tranpsarency put the second image over that then use get image because usally rgb 0,0,0 is transparent in dbp

JUST AN UNTESTED IDEA

Theme park simulator wip

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Zeal

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Posted: 12th Apr 2006 15:46

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@ric

But if you add ANY r, g, or b value to the alpha channel, then youre going to get transparency where there shouldnt be right? And...

"Texture the objects with this new image"

Shwa? If you apply this texture the uvs will be all jacked up.

You might be on to something, but I sure as hell dont get it :p

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Zeal

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Posted: 7th May 2006 06:05

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Well after a couple unsuccessful attempts im back to square one.

Anyone have any other ideas? Again imagine you wanted to take a snapshot of a tree, and then slap that image onto a 2d billboard. How would you capture the alpha of the scene/image?

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Scraggle

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Posted: 7th May 2006 10:03

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There are two methods of grabbing an area of an image and retaining transparency.

Method 1: Use the search button and you will find my code snippet which allows you to do it using memblocks. I will save you the trouble of searching (I know it can be a very difficult task for a lot of people).

`*********************************
`   GET IMAGE WITH TRANSPARENCY
`*********************************
function GetImage(Image1,NewImage,Xstart,Ystart,Xsize as dword,Ysize as dword)
	
	`Find unused memblocks
	Memblock1 = 1
	repeat
		inc Memblock1
	until memblock exist(Memblock1) = 0
	NewMemblock = 2
	repeat
		inc NewMemblock
	until memblock exist(NewMemblock) = 0
	
	`Set up variables
	Local Width as Dword
	Local Height as Dword
	Local Depth as Dword
	Local Red as Byte
	Local Green as Byte
	Local Blue as Byte
	Local Alpha as Byte
	
	`Do it!
	make memblock from image Memblock1,Image1
	Width = memblock dword(Memblock1,0)
	Height = memblock dword(Memblock1,4)
	Depth = memblock dword(Memblock1,8)
	make memblock NewMemblock,(Width*Height)+12
	
	Write memblock Dword NewMemblock,0,Xsize
	Write memblock Dword NewMemblock,4,Ysize
	Write memblock Dword NewMemblock,8,Depth
	
	Position = (Width  * (Ystart)*4) + (Xstart*4) + 12
	NewPosition = 12
	
	for y = 1 to Ysize
		for x = 1 to Xsize 
	   
	      Blue = memblock byte(Memblock1,Position)
	      Green = memblock byte(Memblock1,Position+1)
	      Red = memblock byte(Memblock1,Position+2)
	      Alpha = memblock byte(Memblock1, Position+3)
	      
	      write memblock byte NewMemblock,NewPosition,Blue
	      write memblock byte NewMemblock,NewPosition+1,Green
	      write memblock byte NewMemblock,NewPosition+2,Red
	      write memblock byte NewMemblock,NewPosition+3,Alpha
	      
	      inc Position,4
	      Inc NewPosition,4
	      
		next x
		inc Position , (width*4) - (Xsize*4)
	next y
	
	make image from memblock NewImage,NewMemblock
	delete memblock Memblock1
	delete memblock NewMemblock
	
endfunction

+ Code Snippet

`*********************************
`   GET IMAGE WITH TRANSPARENCY
`*********************************
function GetImage(Image1,NewImage,Xstart,Ystart,Xsize as dword,Ysize as dword)
	
	`Find unused memblocks
	Memblock1 = 1
	repeat
		inc Memblock1
	until memblock exist(Memblock1) = 0
	NewMemblock = 2
	repeat
		inc NewMemblock
	until memblock exist(NewMemblock) = 0
	
	`Set up variables
	Local Width as Dword
	Local Height as Dword
	Local Depth as Dword
	Local Red as Byte
	Local Green as Byte
	Local Blue as Byte
	Local Alpha as Byte
	
	`Do it!
	make memblock from image Memblock1,Image1
	Width = memblock dword(Memblock1,0)
	Height = memblock dword(Memblock1,4)
	Depth = memblock dword(Memblock1,8)
	make memblock NewMemblock,(Width*Height)+12
	
	Write memblock Dword NewMemblock,0,Xsize
	Write memblock Dword NewMemblock,4,Ysize
	Write memblock Dword NewMemblock,8,Depth
	
	Position = (Width  * (Ystart)*4) + (Xstart*4) + 12
	NewPosition = 12
	
	for y = 1 to Ysize
		for x = 1 to Xsize 
	   
	      Blue = memblock byte(Memblock1,Position)
	      Green = memblock byte(Memblock1,Position+1)
	      Red = memblock byte(Memblock1,Position+2)
	      Alpha = memblock byte(Memblock1, Position+3)
	      
	      write memblock byte NewMemblock,NewPosition,Blue
	      write memblock byte NewMemblock,NewPosition+1,Green
	      write memblock byte NewMemblock,NewPosition+2,Red
	      write memblock byte NewMemblock,NewPosition+3,Alpha
	      
	      inc Position,4
	      Inc NewPosition,4
	      
		next x
		inc Position , (width*4) - (Xsize*4)
	next y
	
	make image from memblock NewImage,NewMemblock
	delete memblock Memblock1
	delete memblock NewMemblock
	
endfunction

Method 2. Install update 6 and use the new BITMAP FORMAT 21 command along with a flag of 2 on the GET IMAGE command.

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Zeal

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Posted: 7th May 2006 10:30 Edited at: 7th May 2006 10:33

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Thanks for the input but thats not what im talking about. Im trying to 'get' an image (from 3d space) and retain transparency. So if you took a snapshot of a tree (via set camera to image), I want the backdrop part of the image to be transparent. Sure you could just take the snapshot against a pure black backdrop, and call that area 100% transparent, but I want nice smooth transparent blend along the edges.

Ive tryed taking the snapshot at a ultrahigh resolution, then resampling it down (for the alpha channel) but it still didnt look that great. The main problem is, whatever color you set the backdrop to (when rendering the 3d scene to a texture) shows up in the final image. The 'backdrop' should be colorless.

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Lost in Thought

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Posted: 7th May 2006 12:54

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Does it matter how slow the code is?

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Zeal

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Posted: 7th May 2006 13:52

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Nope this is all pre processing stuff. Just need to make these things then ill save them to a file.

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Lost in Thought

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Posted: 7th May 2006 13:57 Edited at: 7th May 2006 14:09

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I'll come up with something then. I am assuming this is going with your bilboard stuff?

[edit] This isn't perfect, but is it good enough? You can always add a tolerance to clean it up a bit more.

+ Code Snippet

sync on : sync rate 0
backdrop on
color backdrop 0
sync
make object cube 1, 10
sync
get image 1, 0, 0, screen width(), screen height(), 1
delete object 1
make memblock from image 1, 1
delete image 1

wide = memblock dword(1,0)
high = memblock dword(1,4)
deep = memblock dword(1,8)
location = 12
for i = 1 to wide
	for j = 1 to high		
		if memblock byte(1,location) = 0
			if memblock byte(1,location+1) = 0
				if memblock byte(1,location+2) = 0
					write memblock byte 1,(location+3),0
				else
					write memblock byte 1,(location+3),255
				endif
			endif
		endif
		inc location, 4
	next j
next i
color backdrop rgb(0,0,255)
make image from memblock 1, 1
delete memblock 1
make object plain 1, 32, 32
texture object 1, 1

do
	if spacekey() = 1
		set object transparency 1, 1
	else
		set object transparency 1, 0
	endif
	sync
loop

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Xander

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Posted: 7th May 2006 23:44

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Wow, that is a great and simple method LIT. I was actually trying to think of something similar to this for making my game-processed drop shadows. I take a snapshot of the object with a gray texture and then blurred it in a bitmap. I had to use transparency mode 4 to get it to look right, but for some unknown reason, if I use transparency mode 4, then the hardware rendered shadows sporadically appear and dissapear depending on what angle the camera is and what objects are visible. But if I don't use mode 4 then everything is perfect again...

So I am going to base my code off of what you did, if you don't mind, but am going to change it to make a variable alpha channel, because my picture is just grayscale anyway.

Xander Moser - Bolt Software - Firewall

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Zeal

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Posted: 8th May 2006 01:27

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Thanks lost I think I may end up using a colorkey afterall. However I still dont think a simple check like this will work with a complex object. Imagine a semi transparent object like a window. No part of it would be true 000 'black', so not only would it be completely solid, but it would be tinted heavily by the black backdrop.

However this is the most elegant solution. And since this will be used mostly for trees (which dont have a lot of semi transparent parts) I think it will work just fine.

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Lost in Thought

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Posted: 8th May 2006 02:02 Edited at: 8th May 2006 02:04

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Yeah thats why I wrote this instead of using the colorkey (plus I can save the image file with alpha set for other programs). You can add a tolerance to it for some types of objects.

if memblock byte(1,location) >= 0 and memblock byte(1,location) < 10

and etc. But even this fails with some contrasting colors.

[edit] Also the closer you are to the object the cleaner it will be.

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Zeal

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Posted: 21st May 2006 03:58 Edited at: 21st May 2006 04:19

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Well im still struggling with this issue. While a color key type solution does work, it still has one major flaw. The alpha is all or nothing, so whatever color you pick for the backdrop, its going to leave a outline around your final image.

I took a 1024x1024 picture of my tree, then shrunk it down in photoshop to 256x256, and you can see a black outline around the whole thing, it looks like crap (kinda looks like ghetto cell shading).

I just dont see how this is possible unless we could somebow set the backdrop to 'colorless'. Could such a thing maybe be done via a shader? Or is there another solution...

*edit

@dark coder

meant to ask you, you said

Quote: " if you make a 2nd camera and draw it to a corner and remove the backdrop, you can get nice alpha`s annoying that you cant use that for billboards :/."

Whenever I turn off the backdrop, set camera to image just displays garbage in thebackground. Youre saying youve seen it transparent?

*edit again

Oh wait nm youre talking about rendering an actual camera to part of the screen. never tryed that

I think I may have an idea though... What if you set the fog to 100% and colored it pure red, then took a snapshot against a pure blue backdrop. You could use this to get your alpha map (depending on how much blue channel is showing through). Then combine this alpha map with a regular solid snapshot against a grey backdrop (grey is better than black I guess).

That might be as good as its gonna get...

All you need is zeal

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