Towards better color control over an image, we come upon the idea of targeting our actions not on the whole image but on a part of it. Two concepts come into play - the Selection and the Quick Mask.
The actual concept of selection derives from the inherent possibilities of the digital means itself, and opens up creative horizons to the imaginative photographer or image author. We might say in a sense, that a contemporary computer resembles the good old dark room enlarger, but it makes much easier to implement photography techniques that would once take much time and effort and special means. The Selections and the Quick Mask are powerful tools that offer the ability to execute sophisticated operations in the heart of an image. If you are really interested in digital photography, i strongly recommend that you take your time with this Lesson.
Understanding the concept of Selection
If a selection was a spatial concept, that is to say simply refering to an area as a part of the canvas, that would be too simplistic. It can be that as well, but it is not just that, it is something more sophisticated and versatile. And much more interesting!
Technically speaking, the term Selection is rather misleading. Oh oh, one more misleading term? Yes, because it does not refer to a part of an image but to the whole image. But we do have a good reason. Instead of considering space, we do something more creative: we consider the whole image and going down to the pixel level we select every pixel at a given degree. A selection is actually implemented as a 8bit grayscale channel overimposed on the image as a mask on a pixel-by-pixel basis with values between 0-255 for every pixel - so a pixel with 0 value (black) is not selected at all, a pixel with 255 (white) is fully selected, and all intermediate values are possibly present in this specific dynamic range.
Later we will examine the selection tools and their options. Now we will make an introduction to the Quick Mask, oriented towards some interesting possibilities for better color control in continuous tone images.
Tip: working on the Quick Mask directly
In Quick Mask View, if you disable all layers, you can work directly on the Quick Mask just like a normal monochrome.
The Marching Bugs, eh sorry, Ants
In the examples that i have shown in the previous videos, the border of the selection was exactly the dashed line called "marching ants". This is not always the case - and it should not be. In linear drawing it is likely to often be the case. Instead in photography -in continuous tone images- it should not be the case, since normally you should not have an abrupt transition from selected to unselected areas. As already explained, in continuous tone images we often select all pixels as a channel, with every one of them receiving values in the range 0-255. In that case, the marching ants represent contour lines of the pixels that are 50% selected (with a value of 127 in the Quick Mask channel). If you have a really complex selection, those lines may be numerous and annoying enough for you to get rid of them simply by hiding the marching ants.
The selective masking magic
I am trying to induce your imagination to use GIMP effectively. It is important to understand the potential that is hidden under the concept of selective masking. After what you have already learnt, it should not be hard to get the point of the tricks exposed in the next videos.
The term selective masking implies that basically a mask is actually related to a selection. Understanding selective masking will open up horizons for subtle manipulations that might make your photographs more personal and original. Theoretically we might say that every photo that comes out of your camera may pass through some editing, even if it is technically faultless, just to gain your personal creative touch. And very importantly as well, this must be done in ways that avoid histogram problems described in Lesson 5 which can potentially degrade an image.
The following demonstrations obey to this learning approach, not really elaborated in order to yield "a perfect result" but with the intention to illustrate possibilities for targeted manipulations that unleash the potential of the Quick Mask. These demonstrations actually constitute different variations at approaching the critical selection problem.
After these examples i hope that you understand well the power of the Channel Mixer tool as i promised in Lesson 6.
The two types of selective masking
So as you have seen in action, masks are drawables. If you think of it a little, this means that they basically are images. After all that you have learnt on continuous tone images and after watching the masking examples, you probably have the notion that we may consider two types of masking:
- non-continuous tone masking -- basically like using the Threshold tool on the mask,
- continuous tone masking -- basically like using anything but the Threshold tool on the mask.
In example 1, all i needed was a spatial separation of the ball. Instead in example 4, continuous tone masking was my way to go, because i did want to retain the naturality of the image achieving a normal blend of the paint on the wood.
Non-continuous tone masking is good when you want to separate optical items on a yes-no logic, masking things in or out with white or black on your mask. Actually both ways are critical in achieving the separation you want and both ways may be engaged on the same separation task, depending on what exactly you want to do, as done in example 2. Painting on the mask can be made with the Pencil tool for non-continuous tone masking and/or with the Paintbrush tool for continuous tone masking.
No comments:
Post a Comment