Let's Talk About Selections in Photoshop
In this post we will cover one of the most popular topics: selections. You should be up and running after reading this tutorial even if you do not have lots of experience with selections in Photoshop. The secret formula is to understand what are digital images in the first place, to observe a bit existing images and what your camera is sending to Photoshop, how selections are made and to be able to define the problem when it occurs. I will guide you through several steps to get logical conclusions based on the facts and to understand what is your part in the process of making selection, what is Photoshop's side part and how things works.
What are digital images and what your camera is sending to PhotoshopThe first thing you should know is that digital images are, basically digits or numbers. Your JPG file stored on your hard drive does not have any color or square pixels stored inside, there are only digits. As you probably already know, all colors on your screen are created from 3 colors: Red, Green and Blue. Your files contains digits with precise information how much of Red, Green and Blue light should be used to display color for each pixel in your image.
Pixels on your screen are actually digits in the background. That's what Photoshop "see" and have to work with. You may heard that Photoshop see images as channels or grayscale images. That's actually used to give you sense, Photoshop is not human and cannot see as we do. If you see beautiful woman on your screen, that's what you and other, human viewers can see. Photoshop do not know what is woman nor beautiful. When you want to select only woman in your image, Photoshop will do that with little of your help and will perform calculations in the background in addition to some instructions which you can set using text fields and sliders. I will give you more details as we proceed with this tutorial.
Set your expectations properlyNow what is the point of the paragraphs above? The main point is to understand complexity and how things works and to properly set your expectations.
I would like, for example, to press one button and to drink coffee with my friend in Washington DC. That's what I want, make it! I do not care how you will do that, just make it possible! And keep in mind that I do not want to pay high price nor I want subscriptions! Forget about that, make it work perfectly and give me for $5, that's how much I count that job is worth. You are trained for that, that's your job. Do it! Do you hear me, make it now!
In all this I do not have any idea if transmission is even possible, I guess it is. I do not have any idea what problems someone has to solve nor how complex that task is. Sadly, there are people who think in this way and all they have to say are complaints and advices to someone how to tailor everything to their personal needs based on their personal wishes.
Photoshop offers lot of tools for almost every tasks which will help you to create everything that you can imagine. It is not theoretical thing, in practice you can really create anything that can be imagined. Hopefully my post in: how things works series will help you to understand, not what is possible but rather how is possible. In all this process you will need, I believe, basic knowledge, practice and to properly set your expectations so you can avoid wrong conclusions and frustrations.
Closer look to continuous tone digital imageI will use samples in this tutorial which are captured using digital camera, although that's not the only way to create raster type digital image. Lets open one digital image and zoom in to have closer look. I will refer to figure and ground, figure is object we want to select or isolate and ground is what is in the background, behind that object.
I have open image with flower and grass behind it. My little flower is figure and grass is ground. What you must notice is that flower is red and that pixels on the edge starts with red color and then start fading out. This fade out means that as you look toward green (ground pixels) it appears that every next pixel in sequence is actually mix of figure (red) and ground (green) color. Starting from figure to ground, colors are mixed in the way that mix contains more and more of green color and less and less of color red. At the end of sequence there are only green pixels and that's pure ground without flower and its red pixels.
At this point of time you probably have conclusion: do not select pixels in transition area, especially when new ground is different of what is was original ground. If you isolate object from green ground with transitional pixels which are mixture of ground/isolated object pixels (colors) and you want to place isolated object against blue ground, then it won't quite work, right? Red flower captured against blue ground should have, logically, mixture of red and blue color in transition area.
By the way, I am zooming in so you can see what's going on and you can understand what I am talking about. In reality you do not need to closely zoom in each and every time because there are numerous ways to move selection or mask edge for pixel or few pixels inside if needed. One way is using Mask Edge command.
At least you will know why you see some kind of halos even it seems that only figure was selected and extracted. If you know what is the problem it is easy to fix it, especially in Photoshop. We won't spend time in this tutorial on how to modify created selection, you can learn that along the way or to search for tutorials which are numerous on the topic of selections. I am covering in this tutorial what is missing in most of the tutorials and not present on the internet in the amount I think it should be.
At this point of time we should get conclusion that it is always easier and better to work with larger images and larger objects (more pixels-better). It is also worth to have good camera which will not capture very soft edges what is usually case with cheap cameras. We almost always need to select only object without transitional pixels but we also need to make pixels along edges semitransparent so pixels from our object can blend with ground and produce same effect with transition from figure to ground so everything looks nice, realistic and as our object is captured against its new ground.
Colors are actually happy little numbers
You can open Info panel and grab Eyedropper tool to examine what is the difference between RGB values. Move cursor over each pixel and watch numbers in the Info panel.
Now why I am showing and explaining you all this? Because all that colors you see are actually happy little numbers which will be used to create selection. That's what Photoshop have to work with, it is not human and cannot see colors as we do. Photoshop do not have any idea what is flower and cannot judge where are edges of the flower in the way we, humans do. We will see how one of the selection tools works in the next section and keep in mind that in essence, every selection tool or method works in the very same way: using numbers to perform calculations and to make decision which pixels to select.
Now back to expectations
Some of the users would like to have tool which will solve automatically mentioned problems. Keep in mind that computer works with patterns of zeroes and ones. Try to write program which will solve this problem and you will become famous and rich. I would like to move in some other space in second or at least for a few minutes but unfortunately technology is not there and it is question if technology will get there at any time and when. Photoshop from its side offers best available technology, regardless of what some of you think. If Adobe does not have best in the industry then they are simply buying that. Adobe and Photoshop are delivering best available technology and will continue in the following years, I am 100% sure in that. If someone appear with better technology you can guess what will happen so it is safe and recommended to stick with Photoshop. In case you want to do same thing in a different way, then I have plugin recommended for you and that is TopazReask. Actions? I am not recommending because actions has limitations and does not allow developer to bring something new or different of what is already available in Photoshop with a few clicks. If you are looking for automation but you do not have time to learn how to do that, then go and buy actions to create selections.
How selection tools worksAll selection tools in this World works in the very same way: by performing calculations based on the numbers. We will take a look how Magic Wand works and see what is expected from us, users. We have some degree of control which may help us, depend on situation and what we want to select. When you click on image with Magic Wand it will pick numbers beneath and store them. Depend on what is selected from the Sample Size drop-down list it will store RGB numbers of clicked pixel or average of 3 by 3 pixels, for example. Next thing that will happen is to use our instructions from the Options bar. User can check Sample All Layers which means: take in account every pixel on image regardless of where is that pixel, on which layer. Continuous option means selected pixels must be adjacent. Another instruction we can set is Tolerance and this basically means: range of numbers to be included in selection.
Lets say you have set Tolerance to 10. If you have clicked on pixel which is represented as: R = 123, G= 87 and B= 187 then this tool will select all pixels which are in range: R= 113-133, G= 77-97 and B= 177-197 (again to repeat, Tolerance set to 10 with Point Sample from Sample Size drop-down list). That's the magic that will happen. Knowledge about how this and other tools work can be sometimes useful but nobody expect that you will use Eyedropper Tool to measure around before making selection. It usually work with user guess.
There are and many other selection tools in Photoshop like Quick Selection Tool. It also works in the very same way but with different instructions. Quick Selection is even storing information about which pixels (numbers) you do not want to include in your selection.
What about Channels and Apply Image, Calculations commands? In essence it is very similar process where you can use blending modes. Blending modes also deals with numbers and performs calculations using numbers. You can learn much more on how blending modes work from Deke McClelland's tutorials on lynda.com . It's not free by the way, you must be subscriber.
Sometimes those commands can heavily speed up process, it depends on image, what you want to isolate and how familiar you are with blending modes. One of the advantages which are not depended on using Calculations or Apply Image commands is that you can paint on Alpha channel with the Brush Tool and even to use blending modes while painting.
ConclusionHopefully you can understand complexity of the task for which some users asks for one click perfect solution. Technology is still not there and developers are dealing with problem to make everything to work in any situation for any user. That's where things starts to be very complex: in each situation for every user, using numbers!
Now that you know how things works you can start (hopefully) creating perfect selections. Always take in account that sometimes, depend on situation you must do some manual adjustments because nor computer nor any software can see and recognize things as we, humans do.