![\"Figure01\"](\"http:\/\/trappedphotons.com\/blog\/wp-content\/uploads\/2015\/02\/Figure011.jpg\")
<\/a>\nFigure 1: Extracting lightness data<\/strong><\/p>\n
Next, I bring up MultiscaleMedianTransform and make sure it’s reset to the default settings. Then I disable the residual layer (see Figure 2) and and set the Target to Lightness (CIE L*). You may have to change the layers (while keeping the residual layer disabled) depending on your star sizes. For the data I’m working with, 4 layers worked quite well. There will typically be a little nebulosity or galaxy structure left after running this. I use the clone stamp tool to remove the the non-stellar stuff before creating a star mask.<\/p>\n
The second trick is to make several star masks to catch the different star sizes (see Figure 3). This part takes a lot of fiddling. I don’t touch much in the Mask Preprocessing section except the Midtones. For the Mask Generation section I typically leave all options off and vary the Smoothness based on the star sizes I’m trying to re-create (if the start to look square, I up the value some). The other parameters just take experimentation.<\/p>\n Now that you have several different star masks we need to combine them. I like to use PixelMath to do this. Some people use addition but I think that throws things off when you have the same star represented in multiple scale levels, so instead I use the max function (see Figure 4). This way the brightest elements of all three star masks will be combined into on mask. I typically apply this to the image called star_mask and then close the others.<\/p>\n Now that we have an accurate star mask we can start removing stars. Apply your star mask to your image (leave it non-inverted) and then bring up the MorphologicalTransformation tool (see Figure 5). We are going to use the erosion mode which will shrink the stars, pinching in the surrounding data as the star reduces in size. Apply MT to your image and you’ll see the stars get smaller and fainter. Once the stars are almost non existent I switch back to MMT to smooth out the result a little (see Figure 6). Basically invert the layers you had disabled when creating the star_support image, so if you were using 4 layers before with the residual disabled switch that so the first four layers are disabled and the residual is enabled (if your image is in color remember to switch the target to RGB\/K mode). Figure 7 shows a sequence of how the stars were reduced in this image where the first 6 tiles were using MT and the last 2 using MMT.<\/p>\n<\/a>
\nFigure 2: MultiscaleMedianTransform used to remove larger structures<\/strong><\/p>\n<\/a>
\nFigure 3: Three passes of StarMask to capture different star sizes<\/strong><\/p>\n<\/a>
\nFigure 4: Combining star masks with the max function in PixelMath<\/strong><\/p>\n<\/a>
\nFigure 5: MorphologicalTransformation in Erosion mode<\/strong><\/p>\n<\/a>
\nFigure 6: MultiscaleMedianTransform being used to remove stars<\/strong><\/p>\n<\/a>
\nFigure 7: Sequence of star reduction<\/strong><\/p>\n