Raster and vector images in Photoshop. Rasterization in Adobe Photoshop CS5
Almost all beginners cannot master Photoshop because they are intimidated by working with layers in Photoshop. They don't understand her.
But everything here is quite easy - you just need to know the basic rules and actions.
I promise you that you will understand them and begin to put them into practice! And so - let's get to work!
Let's look at all the steps using the example of creating a video screensaver.
In addition to creating a video intro, we will learn:
- how to move layers in photoshop
- how to rasterize a layer in photoshop
- how to create a new layer in photoshop
- how to copy a layer in photoshop
For a more visual understanding of this, at first glance, complex topic, I created a video where I discuss in detail all the above-mentioned features of working with layers in the process of creating a video screensaver. If it’s easier for you to perceive video material, go to the end of the article. But I recommend both reading and watching, because then there is a chance that you will easily learn everything that will be posted here.
How to select a layer in Photoshop. Layers panel
When you open the Photoshop program (I use Photoshop CS6), on the right toolbar we find the inscription “Layers”:
We click on it with the left mouse button and we get into the layers panel, in which we will constantly be located when creating any drawing:
For normal operation, you always need to know which layer you are on. Whichever layer is selected is where you are. The selected layer in the panel is always a different color - mine is blue. If you need to carry out some actions on a certain layer, you first find it in the layers panel, stand on it and click on it with the left mouse button - it is highlighted in color and you can already work with it (see the picture above).
There are different buttons on the layers panel. We will now learn the most popular ones (I numbered them in red numbers). Thanks to them, we can do different actions with the selected layer.
How to create a new layer in Photoshop
Click on the layer inscription on the panel (Fig. 1), go to the selected layer (Fig. 2). If we need to add styles to our layer, click the icon number 1 (the label on the button is fx). A window with styles will appear and we select the one that will improve our fragment of the picture.
If we need to create a new layer, click on the shape number 2 (in the film I looked at adding a layer with a gradient in great detail). The new layer always appears on top of the selected one. I recommend naming the layers.
If you need the layer to appear below the selected one, press simultaneously the “Ctrl” button on the keyboard and button 2, which is called “Add Layer”.
How to remove layers
If you experimented and realized that the layer is unnecessary, you can remove it from the drawing in two ways - click the drawn eye in the panel next to the layer - it will then simply become invisible, or hold down the left mouse button and drag it to the trash can (number 3). The layer will be deleted.
There are some other nuances of working with text layers, but we will look at them in a separate article.
Before you start watching the video, I’ll make a small clarification for dummies:
if you need to transfer a picture from your computer to a Photoshop field, press it with the left mouse button and drag it onto the Photoshop work area (I couldn’t think of this at the time!!!).
Let's watch the video and see how I work with layers, creating a video screensaver for the same video that you are watching:
I don’t allow you to download the lesson materials - find the pictures yourself on Google with which you want to create a similar composition. The only thing is when searching, add the word - without a background.
Or Gradient, then you won’t succeed. Photoshop will display a dialog box telling you that you will have to rasterize this layer first.
Why? First you need to remember what vector layers actually are. In the article I have already described in detail how they differ. In short, the difference is what these layers are made of: for a raster, these are pixels, for a vector, these are figures based on mathematical formulas.
Since Photoshop is designed primarily to work with raster images, most tools in one way or another affect exclusively pixels, that is, raster images. Therefore, when in Photoshop we still need to work with a vector layer (and when can we get it? - for example, we created or ), but for this we take tools created only for rasters, then Photoshop shows us the error indicated above.
Let's say we created a shape layer:
Now I want to apply a blur effect to this star or draw something else on top of it, but the program will show an error and inform you that you need to first rasterize the layer.
In other words, Photoshop can convert the contents of a layer from one type of image - vector, to another type - raster. This process is called rasterization.
It is noteworthy that there is no reverse process from raster to vector in Photoshop. Take this fact into account.
Note
Keep in mind: once you rasterize a layer, there is no going back. You will lose the advantage of a vector image - resizing without losing quality. For beginners, it is recommended to rasterize on a duplicate layer - then you can always return to the original. before rasterizing, and then the original layer, so as not to accidentally rasterize the wrong layer.
How to rasterize a layer
Rasterizing a layer is easy: right-click on the vector layer. The menu context will contain the command Rasterize layer(Rasterize). Click it and Photoshop will do everything.
If you notice an error in the text, select it and press Ctrl + Enter. Thank you!
Printing processes require illustrations in the layout that are processed in a special way. Halftone one-color illustrations should be rasterized, and colored ones also color separated. For printing, the layout is supplied on a transparent film in full size. The document is output to film using phototypesetting machines. In the roughest approximation, they are similar to laser printers, only the laser illuminates not the light-sensitive drum, but the photographic film. All phototypesetting machines use the PostScript language and have a print resolution several times higher than the best printers (an average of 3600 dpi). Phototypesetting machines are very expensive and complex devices that not every product can afford to purchase. To output original layouts, as a rule, they resort to the services of servers specializing in pre-press preparation.
Linear rasters
Rasterization is used by almost all digital display devices: from monitors to printers. Its essence lies in dividing the image into small cells using a so-called raster grid. In this case, each cell has a solid fill.
Methods for transmitting halftones in analog (photography) and digital (prints, printing presses) processes are fundamentally different. If you look at an image printed in a printing house or on a laser printer, it is hard to notice that it consists of many small dots, which are called raster. Most often, the points are located regularly, at the same distance from each other, forming linear raster, or raster grid. In the Middle Ages, a special method of rasterization ( frequency modulated), using an irregular arrangement of raster dots. The raster they form is called irregular, or stochaic. In Fig. 17.9 shows a rasterized image.
Rice. 17.9. Rasterized image
Unlike photography, a halftone dot cannot have any coloration - it is always black. To convey shades, raster dots of different sizes are formed during the screening process. Between the thicker points, on-
printed in adjacent cells of the raster grid, little white space remains. This creates the illusion of a darker shade of color in the area. Conversely, smaller dots printed at the same spacing leave most of the bugs in the space between them white. This gives the impression of a light shade (Fig. 17.10).
Rice. 17.10. Simulating dark and light shades of gray using a raster
Digital rasters
Rasterization by digital methods is organized in a different way. The invention in laser printers and phototypesetting machines is created by laser scrap. The beam cannot have a variable size, which is necessary to obtain rar points of varying size. Therefore, the rasterization process involves combining “real” dots created by a laser beam into groups that form raster dots.
Such a raster is a collection of square cells into which the image is divided. Each cell is allocated for one raster point. A point, in turn, consists of a group of "real" points of the same size, created by an output device. The larger part of such a cell is covered with printer dots, the larger the size of the raster dot they form and the darker shade of gray it conveys. For example, in order to fill an area of an image with 50% gray, the rasterization program (rasterizer) will fill this area with raster dots, each of which will represent a half-filled raster cell. If it is necessary to transmit 25% gray, the raster cells are filled with black only to the extent of black (Fig. 17.11).
Rice. 17.11. 2 50% rasters under magnification
Printer dots in a raster cell can occupy different positions. The shape of the raster dot depends on this. In printing, various raster dot foils are used, but the most traditional and widespread is round. Several examples of supported raster dot shapes are shown in Fig. 17.12.
a B C D
Rice. 17.12. Various dot shapes:
A- round; b- elliptical; V - square; G- linear
Please note that the number indicated in the printer's passport as resolution (for example, 600 dpi) represents the number of “real” dots that the printer can produce on a single segment 1 cm or 1 inch long. The number of raster points per unit length (raster grid pitch) is called lineature and is measured in so-called lines per inch(lines per inch, lpi) or lines per cm(lines per centimeter, lpc). Since several real dots are required to form a raster dot, the lineature of the raster image is always lower than the printer resolution.
Lineature and number of shades of gray
The ratio of the resolution of the output device to the raster lineature gives the size of the side of the raster cell, measured at printer points. The maximum number of printer dots that form a halftone dot is equal to the square of the cell side. So, for example, if the raster lineature is set to 100 lpi, and the printer resolution is 600 dpi, the side of the raster cell will be equal to 600/100 = 6 pixels. Under these conditions, the raster dot is formed from 6 6 = 36 printer dots.
The visible quality of illustrations also depends on the screen lineature. The higher the lineature, the less noticeable the dots that form the raster are, and the print is closer to the photographic original. As you can see, the 50 lpi we obtained is a very small value. If you print an illustration the size of a postage stamp with such a lineature, it is unlikely that you will be able to determine what is depicted on it. After all, each raster grid page will contain only 50 points.
When printing on an office printer, in order to increase the raster lineature, you have to sacrifice the number of transmitted shades of gray. In most 60-point printers, the default screen lineature value is 85 lpi. With this lineature, the number of shades of gray in the images does not exceed (600/85)2 + 1 = 50. This is three times less than the minimum defined at 150 shades. Hence the low quality of image printing on office laser printers (Fig. 17.13).
a B C
Rice. 17.13. Image,
printed with lineatures: A- 50 lpi; b- 85 lpi; V- 100 lpi
Color separation and screening
Color documents present a more complex case of rasterization. Orinal layouts for them should be presented in the form of several films: one for each applied paint. The division of a color image into separate paints (components) is called color separation. The simplest case is the use of spot colors, when each of them is displayed on a separate film. The halftone concept allows you to use shades when working with spot colors. A more common case is the color separation of full-color documents, where four inks of the CMYK model, also called triadic. Consequently, full-color documents are output using a phototypesetting machine onto four films corresponding to the base colors of this model.
Normal
15° Blue 15°
75° Magenta 80°
0° Yellow 0°
45° Black 55°
Rice. 17.14. Angles of inclination of rasters of basic colors when printing with process inks and the pattern of moiré occurrence
Each color is rasterized separately with different raster grid angles. Traditionally, the tilt angle when printing monochrome documents and printing
spot colors is 45 - this value is time-tested and provides the best masking of the linear structure of the raster.
You have to deal with different raster angles almost exclusively when printing with process colors. One of the reasons is that it is simply impossible to apply process inks to a sheet without changing the raster angle - otherwise the color dots corresponding to the base colors will be printed on top of each other.
The angles of inclination of the rasters for the basic colors are selected in such a way that all points are visible - without this, the colors will not be able to visually mix inside the human eye, forming the desired color. Ultimately, the raster angles must be such that the base color dots are grouped into rosettes (see top left image in Figure 17.14). Each such rosette can be thought of as a certain meta-point of a color raster, forming a color in a given image volume.
The top right image in Fig. Figure 17.14 illustrates another reason why such significant attention must be paid to the angles of inclination of the base color screens when printing with process colors. If these angles are not consistent, moire appears on the image - dirty waves. Moire is a common defect in color reproduction.
Users who have just started learning Photoshop have many questions. This is normal and understandable, because there are nuances that those who want to achieve high quality of their work in Photoshop simply cannot do without knowing.
These undoubtedly important nuances include the rasterization of images. Don’t let the new term scare you – as you read this article, you will easily understand everything.
First of all, let's understand that there are two types of digital images: vector and raster.
Vector images consist of simple geometric elements - triangles, circles, squares, diamonds, etc. All simple elements in a vector image have their own key parameters. These include, for example, the length and width, as well as the thickness of the border lines.
With raster images, everything is much simpler: they represent many points that we used to call pixels.
How and why to rasterize an image
Now that there are no questions about the types of images, we can move on to the most important thing - the rasterization process.
Rasterizing an image means turning a picture that consists of geometric elements into one that consists of pixel dots. Any graphic editor similar to Photoshop allows you to rasterize a picture if it supports working with vector images.
It must be said that vector images are a very convenient material, because they are very easy to edit and change in size.
But at the same time, vector images have a significant drawback: they cannot be used with filters and many drawing tools. Therefore, in order to be able to use the entire arsenal of graphics editor tools in your work, vector images must be rasterized.
Rasterization is a quick and completely uncomplicated process. You need to select the layer you are going to work with in the lower right Photoshop window.
Then right-click on this layer and select the item in the menu that appears "Rasterize".
After this, another menu will appear in which you can select any item we need. For example, smart object, text, fill, shape etc.
Actually, that's all! It is no longer a secret to you what types of images are divided into, why and how they need to be rasterized. Good luck in your creativity and learning the secrets of working in Photoshop!
