CGTalk - Checking a bitmap's alpha value

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TheGrak

03-19-2011, 06:36 AM

I want to loop thru a bitmap's values until I come across the first instance of a non 0 alpha value.
How would I go about doing this, say for example in this context:

local myPSDlayer = bitmapLayerManager.LoadLayer aPSDfile 1 true

Something like:
for thePixels in myPSDlayer.pixelData do
if thePixel.value != 0 then print "value>0"

Thanks! :)

03-19-2011, 12:57 PM

you need to iterate over the pixels row by row using getpixels method. Get a row each time then iterate over each pixel of that row and check its .alpha property.

Panayot

03-19-2011, 01:39 PM

If the case is just to test wheter the bitmap has alpha then this will save your time:
<bitmap>.hasAlpha

TheGrak

03-19-2011, 08:52 PM

@Lo - thanks! thats what i needed.
@Panayot - i have to check each pixels value, but that's a handy code snippet.

Here is what I ended up using:

--iterate over the pixels row by row using getpixels method.
for g = 0 to myBitmapHeight by 1 do --for the height of the bitmap
(
local myPixelRow = getPixels myFullframebitmap [0,g] myBitmapWidth --get a row of pixels
for j = 1 to myPixelRow.count do --for every row of pixels
(
if myPixelRow[j] != (color 0 0 0 0) then --if the pixel isn't completely transparent
(format "Opaque found at: [%,%]" g j)
)
)

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03-19-2011, 08:52 PM

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