[Image-SIG] Transparent colored overlay effect
Tue, 29 Sep 1998 11:19:58 -500
I'm implementing a principal component analysis of multivariate images
application (same sample taken at multiple wavelengths) and need help in
achieving a desired effect.
From various computed images, the user selects regions, each of which identifies
certain pixels in another computed image. This later image I'll call the overlay
image. I would like to render the overlay image with the identified pixels
"shaded" a selected color; i.e. you can still see the gray-scale intensities
thru a "tinged" color (I've seen this in other commercial apps...).
Currently, all I can achieve is to draw these pixels in opaque colors as follows:
The overlay image is a gray scale image scaled so that all pixel values are
between 0 and 255 - (max number of possible colored overlays), then converted to
an RGB image.
Then, given a list of masks (255 at the pixels of interest, 0 everywhere else)
and colorLut (the 256 gray scale ramp):
lut = copy.copy(colorLut)
rlut, glut, blut = lut[:256], lut[256:512], lut[512:]
i = 0
for img in self.masks:
nV = 255 - i
pasteImg = img.point(lambda p,nV=nV: p==255 and nV)
rlut[nV], glut[nV], blut[nV] = rgb(_overlayColorsUsed[i])
i = i + 1
newImg = overlayImg.point(rlut+glut+blut)
newImg now shows the original image with each mask showing in an opaque color.
Any ideas on how I can get the overlain masks to be "slightly" transparent so
that the underlying gray scale intensities are still discernable?
Cambridge Research & Instrumentation