I not sure if I undertand your question, but if you are looking to do some image overlaping, as does photoshop layers, you can use some image characteristics to, through that characteristc, determine the degree of transparency.
For example, consider using two RGB images. Image A will be overlapped by image B. To do it, we ll use image B brightness to determine transparency degree (255 = 100%).
Intensity = pixel / 255;
NewPixel = (PixelA * (1 - Intensity)) + (PixelB * Intensity);
As intensity is a percentage and each pixel is multiplied by the complement of this percentage, the resulting sum will never overflow over 255 (max graylevel)
int WidthA = imageA.Width * channels;
int WidthB = imageB.Width * channels;
int width = Min(ImageA.Width, ImageB.Width) * channels;
int height = Min(ImageA.Height, ImageB.Height);
byte *ptrA = imageA.Buffer;
byte *ptrB = imageB.Buffer;
for (int y = 0; y < height; y++)
{
for (int x = 0; x < width; x += channels, ptrA += channels, ptrB += channels)
{
//Take the intensity of the pixel. If RGB (channels = 3), intensity = (R+B+G) / 3. If grayscale, the pixel value is intensity itself
int avg = 0;
for (int j = 0; j < channels; ++j)
{
avg += ptrB[j];
}
//Obtain the intensity as a value between 0..100%
double intensity = (double)(avg / channels) / 255;
for (int j = 0; j < channels; ++j)
{
//Write in image A the resulting pixel which is obtained by multiplying Image B pixel
//by 100% - intensity plus Image A pixel multiplied by the intensity
ptrA[j] = (byte) ((ptrB[j] * (1.0 - intensity)) + ((intensity) * ptrA[j]));
}
}
ptrA = imageA.Buffer + (y * WidthA));
ptrB = imageB.Buffer + (y * WidthB));
}
You can also change this algorithm in order to overlap Image A over B, in a different place. I m assuming here the image B coordinate (0, 0) will overlap image A coordinate (0, 0).
But once again, I m not sure if this is what you are looking for.
