Here are the steps I used:
- I’m assuming the image was not white balanced. In the future, be sure to white balance the camera before taking images.
To white balance the image post-processing, I used Image->Color->Split Channels to get each color channel, drew a selection on the background, used Ctrl+Shift+E to transfer the same selection to the other two backgrounds, and used Ctrl+M to measure the mean intensity for each image. I then used Process->Math->Multiply such that all of the images had the same background intensity:
- The problem is then to get what is only red, however, after white balancing the droplets are now pink. Since white = red + green + blue, pink = red + blue, and yellow = red + green, then objects that are red->pink (i.e. contain both red and some blue) can be calculated as red channel - green channel. By subtracting the green channel from the red channel, we are removing any white, and yellow objects in the red channel, and keeping the red and pink objects.
To subtract the green channel from the red channel, use Process->Image Calculator. This will create an 8-bit image with only red and pink objects:
The image looks pretty bizarre, however this is purely because it is a JPEG image, and JPEG is a lossy compression, where a lot of the original image information gets erased. By subtracting the green from the image, we’ve unmasked the blocks of JPEG compression. Images for analysis should always be saved as uncompressed Tiffs or bitmaps (preferably tiffs) since these will preserve all of the original image.
With the above 8-bit image, you should be able analyze it using you plugin of choice.