Light/dark lines tutorial
Step 1: Select your brush, color, and thickness
I use a basic hard brush, with black and white, and thickness will change depending on image size. I typically use 2-4 px, maybe even 1 px for fine lines like around the eyes. You can select your light and dark colors from the horse. I tend to use just black and white as they stand out better since we will be smudging and messing with opacity.
Step 2: Start drawing in lines
I personally like to start at the head and work my way down but it really doesn't matter. First you will need to create a new layer DO NOT draw on the horse. Just zoom in on where you want to get started and basically follow the natural contours and highlights of the horse. To bring out the most detail you must be very meticulous, sometimes even adding lines that aren't really there. I also like to add lines where body parts cross over each other in order to avoid them looking blended together. If your horse image is poor in quality you can use references to help guide you. For example if the stock I'm working with doesn't show as much detail as I would like.
I would pull up an image with more detail and add in lines from the better image. Oh I also use a stabilizer to pull straight lines, this is not required but does make it a bit easier. Once you have all your lines placed you are ready for step 3, my least favorite.
Step 3: Smudging T-T
Once all your light lines are done, time to whip out the smudge tool! Most of the time settings will vary depending on what program you are using, I use affinity photo. I use 25% flow and 40% strength, feel free to edit as needed or do something totally different. I also use a basic hard brush and a 15-20 px brush, yours may vary just use a slightly bigger size than the lines. You will want to go in and smudge the ends of each line, and do 1 or 2 passes over the whole line. Remember not to smudge too much as we will be editing opacity. This step is very important, if you don't smudge the ends your lines will be too harsh. Usually during this step you will end up adding a few more lines. When smudging be sure to follow the direction of the line!
Step 4: Final Edits
Now this is where you will want to edit the layer settings. This step is 100% up to you, do what you think looks best. Normally I just mess with opacity until I get a natural look. You can however change the layer type to soft light if needed. But yeah just play around with the settings until it feels right. During this step you may find lines that just don't look right or stand out too much just erase them.
Now just do these steps all over again but with your dark color, following the darker contours of the horse. Remember you don’t have to follow my method exactly, this is just what I prefer.