OK, that makes a lot of sense; sometimes, I just need another set of eyes to see the flaws in my code! 
Thanks again!

	-----Original Message----- 
	From: squeak-dev-bounces at lists.squeakfoundation.org on behalf of Bert Freudenberg 
	Sent: Thu 7/22/2004 3:35 PM 
	To: The general-purpose Squeak developers list 
	Cc: 
	Subject: Re: Using video input in Squeak
	
	

	Well, in this case, why do you allocate a new form at all? Just
	overwrite the values in the one you got! Also, for speed, do not build
	the colorMap inside the loop, but before:
	
	initializeProcess
	
	    | colorMap threshold |
	    frame := Form extent: self decoderSize depth: 16.   "must be 16, or
	you need a different colorMap"
	    threshold := 0.5. "tweak here"
	    colorMap := ColorMap shifts: #(0 0 -5 0)
	       masks: #(0 0 2r000001111100000 0)
	       colors: ((1 to: 32) collect: [:i | i < (threshold * 32)
	          ifTrue: [Color black pixelValueForDepth: 16]
	          ifFalse: [Color white pixelValueForDepth: 16]]).
	       
	    process := [[
	        self decoderRequestCapture.
	        frameSemaphore wait.
	        self decoderCopyLastCapturedFrameInto: frame.
	        (BitBlt toForm: frame)
	                copyForm: frame to: 0 at 0 rule: Form over colorMap: colorMap.
	        ] repeat] forkAt: self decoderProcessPriority.
	
	This code is untested, of course, but I doubt you can get much more
	efficient than that ;)
	
	- Bert -
	
	Am 22.07.2004 um 19:09 schrieb Rob Hensley:
	
	> OK, I'm almost there! The version I'm working with now (including
	> you're wonderful suggestions!) displays exactly ONE frame of the B/W
	> image (Woo Hoo!) but then blows up. This is the code:
	>
	> initializeProcess
	>
	>    | colorMap bwFrame |
	>    frame _ Form extent: self decoderSize depth: Display depth.       
	>    process _ [[true] whileTrue: [
	>       self decoderRequestCapture.
	>       frameSemaphore wait.
	>       self decoderCopyLastCapturedFrameInto: frame.
	>       colorMap _ ColorMap shifts: #(0 0 -5 0)
	>               masks: #(0 0 2r000001111100000 0)
	>               colors: ((1 to: 32) collect: [:i |
	>               i < 16 ifTrue: [1] ifFalse: [0]]).
	>       bwFrame _ Form extent: frame extent depth:1.
	>       (BitBlt toForm: bwFrame)
	>               copyForm: frame to: 0 at 0 rule: Form over colorMap: colorMap.
	>
	>       "Here's the problem: the class I am extending wants to display
	>       frame (which MUST be of depth 16 or greater), not bwFrame
	>       (which is of depth 1), so I need to get bwFrame's revised
	>       colorMap back to depth 16 before I make frame equal to
	>       bwFrame. This is why it is blowing up. Any ideas?"
	>
	>       frame _ bwFrame.
	>       ]] forkAt: self decoderProcessPriority.
	>
	> -----Original Message-----
	> From: squeak-dev-bounces at lists.squeakfoundation.org
	> [mailto:squeak-dev-bounces at lists.squeakfoundation.org] On Behalf Of
	> Bert Freudenberg
	> Sent: Thursday, July 22, 2004 4:38 AM
	> To: The general-purpose Squeak developers list
	> Subject: Re: Using video input in Squeak
	>
	>
	> Am 22.07.2004 um 03:58 schrieb Dean_Swan at Mitel.COM:
	>
	>>
	>> Hi Rob, Bert, Jack:
	>>
	>> Form asGrayScale actually does extract the green component from 32 bit
	>> forms, or converts a lower depth Form to a 32 bit form and then
	>> extracts the green component.  It is NOT however, a single BitBlt
	>> call.  It does a copyBits for each column, and some fancy form/bitmap
	>> substituion to treat the 32 bit form as if it were an 8 bit form four
	>> times as wide.
	>
	> I think the asGrayscale method is older than the ColorMap class, which
	> is a rather recent extension to the original BitBlt. For performance,
	> it should be rewritten now.
	>
	>> How would you accomplish this with only a "single BitBlt call"?
	>
	> ==== snip ====
	> | orgForm bwForm |
	> "Make a dark shape on light ground"
	> Display getCanvas
	>       fillRectangle: (0 at 0 extent: 400 at 300) color: Color yellow;
	>       fillOval: (100 at 100 extent: 30 at 50) color: Color blue.
	> orgForm := Form fromUser asFormOfDepth: 16.
	> "setup colormap to extract green component and map to 0 or 1"
	> colorMap := ColorMap shifts: #(0 0 -5 0)
	>       masks: #(0 0 2r000001111100000 0)
	>       colors: ((1 to: 32) collect: [:i | i < 16 ifTrue: [1] ifFalse: [0]]).
	> "16 = threshold of 0.5"
	> "This should also be allocated only once "
	> bwForm := Form extent: orgForm extent depth: 1.
	> "Do this every frame"
	> (BitBlt toForm: bwForm)
	>       copyForm: orgForm to: 0 at 0 rule: Form over colorMap: colorMap.
	> "Done"
	> bwForm display
	> ==== snap ====
	>
	> For 32 bpp, you of course need to tweak the shifts, masks, and colors:
	>
	> ColorMap shifts: #(0 0 -8 0)
	>       masks: #(0 0 16r00FF00 0)
	>       colors: ((1 to: 256) collect: [:i | i < 128 ifTrue: [1] ifFalse:
	> [0]]).  "128 = threshold of 0.5"
	>
	> I guess the 16 bpp version will be faster, but you should use whatever
	> the plugin delivers fastest. You should avoid the conversion to another
	> depth unless it is really necessary. Also, all constant calculations
	> should be moved out of the inner loop (the one that fetches images from
	> the camera and processes them).
	>
	> Also, if your destination bitmap is not of depth 1, the colors in the
	> ColorMap of course need other PixelValues:
	>
	> String streamContents: [:s | #(1 8 16 32) do: [:d |
	>       s print: d; nextPutAll: ': '.
	>       {Color black. Color white} do: [:c |
	>               s nextPutAll: (c pixelValueForDepth: d) hex; space].
	>       s cr]]
	>
	> 1: 16r1 16r0
	> 8: 16r1 16rFF
	> 16: 16r1 16r7FFF
	> 32: 16rFF000001 16rFFFFFFFF
	>
	>> Rob, just a caveat using Form>>asGrayScale - It is an approximation.
	>>  I tried it using a workspace as the test bitmap, and the selected
	>> text didn't come out as selected because with default colors, selected
	>> text is black on a bright green and the background is bright white.
	>>  This leads to what looks like no selected text in the grayscale
	>> version, where the "properly" calculated Form>>yComponent method does
	>> show the selected text as black on medium gray.
	>
	> You just have to adjust the threshold ...
	>
	> - Bert -
	>
	
	
	

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