Lattice format image

How does the image we see constitute it? This needs to involve the concept of image type.

The image type in computer is divided into two kinds, one is called dot Matrix, the other is called vector graph.

As the name of a bitmap is composed of dots, as with mosaic to collage patterns, each mosaic is a point, several points in the matrix arranged into patterns.

Photos taken by digital cameras, scanner scans, and most of the pictures belong to the bitmap, as the following figure is a typical bitmap:

Turn this picture into Photoshop and use the menu "image > Image size" To see the following information:

Note the width and height in the upper pixel size, which are 400 pixels and 225 pixels respectively.

What is a pixel? Pixels are the dots that make up the bitmap image, which is the smallest unit of the bitmap. As many mosaics as the pattern.

On the left side of the Photoshop status bar, zoom to the right of the area, alt-Click also appears the number of pixels information, if there is no status bar available menu "Window > Status bar" Open. The following figure:

If we enlarge the image 〖ctrl +〗, we will see the point is also magnified at the same time, there will be so-called mosaic phenomenon (also known as sawtooth phenomenon). The following figure:

We can see that there are a lot of different colors of small squares, that is magnified pixel. There can be only one color per pixel.

400 pixels wide, 225 pixels high, meaning this image from the transverse direction of 400 points, vertical direction 225 points, 400x225=90000, the total number of pixels of the image is 90,000.

The digital camera has a very important indicator is 3 million pixels, 5 million pixels of the salutation, that is, the total number of pixels taken out of the image.

The shortcut key for zooming in on the image is 〖ctrl +〗〖ctrl-〗, which is magnified along the center point of the image.

Another way to zoom in is to hold down the space and CTRL keys and click on one part of the image with the mouse, which zooms in as the center of the click. Zoom out is to hold down the spaces and alt-click.

If the zoom level is not enough you can repeat the above operation. The title bar of the image window, along with the left end of the status bar under Photoshop, displays the zoom multiples.

Strictly speaking, you should press CTRL and then press the blanks. But in Chinese windows this is just the default Chinese input method to switch. It is therefore recommended that you press the CTRL key before pressing the space.

If the image exceeds the size of the image window, the scroll bar appears to the right and below, pulling the scroll bar to move the viewing area (not moving the image).

You can also hold down the SPACEBAR and drag the mouse down in the image. When the mouse starts dragging, the SPACEBAR can be loosened.

Some of the above shortcuts are most commonly used. To keep them in mind, this will make your operation faster.

Is the more pixels the better? In most cases, yes, the more pixels of the image, the more detailed the recorded information, the more detail the local image, the following figure:

Figure is a total of 1.44 million pixels (1600x900) of the image, in the magnification to the same size as the previous picture, it is obvious that the image part to appear much more delicate.

Our display is also a dot-matrix, and the TV screen seen in the previous lesson is made up of many dots. This is true for both LCD and plasma screens.

The traditional CRT display, also known as the cathode ray tube, is the earliest and most popular type of display equipment.

The number of dots in the display is variable, and we can view or change the screen resolution of the current monitor from the display items in the Windows Control palette, as shown below:

As shown in the picture, currently is 1024x768 pixels, that is, now the display can display the horizontal direction of 1024 points, vertical direction of 768 points.

Like a 6-inch picture that doesn't fit into a 5-inch frame,

If an image exceeds the number of pixels in the horizontal or vertical direction of the display, the image cannot be fully displayed on the screen (100% without scaling).

So the higher the screen resolution, the more content you can fully display. For example, a 300x300 pixel box, at different screen resolution, the displayed size is not the same, the following 3 figure:

As a manhole cover on the road, standing on the 5 floor to see very clearly, standing on the 30 floor is a lot smaller, standing on the 70 floor is even smaller. The actual size of the manhole cover has not changed, and the enlarged field of vision causes the manhole cover to shrink.

So this does not mean that the size of the box has changed, 300 or 300 pixels have not changed, because the increase in total screen pixels makes it look smaller.

The calculation will know that when the screen resolution 800, 300 pixels occupy about half the width, occupy about One-third in 1024 time, occupy about 1600 in one-fifth time only.

There are many dots on the display, each of which is made up of red-green-blue three-phosphor-coated units, the scientific name being pixels.

Inside the monitor, a part called an electron gun is used to excite the pixel, which emits three electron beams hitting the top-left corner of the screen (which can be called 0 points) and the three beams hitting the red, green and blue units respectively.

According to the strength of the signal, the red, green and blue are mixed in proportion. This completes the excitation of a pixel.

Then, under the magnetic force of the deflection yoke, the electron beam moves one pixel to the right and then the pixel is excited. Until the order fires all the pixels in this line. is called completing a "row scan."

Then move down one line, back to the left to start firing the first pixel of the second row. So repeat. When the last pixel of the last line is fired, a "field scan" is completed.

As a result, the pixels on the screen are not luminous at the same time, but because the human eye has a visual retention characteristics, so still can see a complete picture.

The sequence of the monitor scans is as follows, from 0 o'clock to the x axis, after completing a line and moving to the Y axis for a second line of scanning.

Because of this type of scanning, the coordinates of the screen are the same as above, with the upper-left corner as the origin, the x-axis to the right, and the y-axis downward. This is just upside down from the plane geometry coordinate system.

When we store the image in a dot matrix format, Photoshop records the color of all the pixels in the image, one after the other, in the order shown above. Thus storing the image.

When you open a bitmap image in Photoshop, the pixel information is extracted and displayed on the screen in the order listed above.

When we browse the Web, we sometimes see that the picture doesn't appear at once, but it shows up from top to bottom. This is because the slow speed of the network transmission is caused by the slow reading of dot-matrix pixel information.

If you wait for a long time to transmit, you will lose interest to the viewer. Therefore, the pictures on the Web page should be as small as possible to facilitate rapid transmission. We will be in touch with this point in the future.

Photoshop Information palette will display the current mouse in the image of XY coordinates, the following figure mouse hotspot is in this image in the horizontal direction of the 93rd, vertical direction of the 50th pixel:

The so-called mouse hotspot refers to the mouse cursor in the role of that point, different cursor hotspot location is not the same. The hot spots on the top of the diagram are at the sharp corners of the arrows.

After understanding the difference of the size of the lattice image, we know that the larger the lattice image format, the more pixels, the richer the information recorded.

But if only a small picture, can enlarge it? What about the effect of amplification later than the real big picture? Now let's do an experiment.

First open the picture in Photoshop, as shown in the following figure:

Use the menu "image > Image size" To change the width to 200, and note that the height also varies, because the constraint scale option below is valid. This will keep the picture wide and high proportions unchanged.

The other options in the dialog box are not to be delved into at the moment. You can refer to the following figure:

Press the Good button to determine the operation, you will see the image has become smaller. The following figure:

After this step, we shrink a large image to a small graph, changing from 90,000 pixels (400x255) to 22600 pixels (200x113).

Now use the menu "image > Image size" again to change the image width back to 400. Note that the height calculated automatically is 226 instead of the original 225. You will see the following image:

The image became blurred, and some of the details (such as the fingers of the left hand) that had been visible were lost. What is this for?

First, let's simulate the first narrowing process, assuming we're going to shrink the image of a 10x6 pixel to 5x3, and here's the schematic, each gray square representing 1 pixels:

When the instruction is reduced, Photoshop extracts pixels and discards them, as shown in the following figure:

The remaining pixels are then pieced together to form a reduced pattern, as shown in the following figure:

After the first narrowing, the pixel dropped from 90,000 to 22600, which dropped 67,400 pixel information. The image is then extended to 400x225 pixels, although the total pixel size is 90,000,

However, the 67,400 pixel information discarded in the first conversion is not returned. Photoshop can only use the interpolation algorithm to compensate for these 67,400 pixels.

The so-called interpolation algorithm, just like guessing, to "fabricate" those who do not exist in pixels. The following diagram is the 2x2 part of the upper-left corner of the above picture:

Existing A, B, C, D four pixels, to extend the 2x2 to 3x3, then more than 5 pixels. The markings in the figure are 1, 2, 3, 4, and 5.

How do you determine the color of a pixel that didn't exist originally? is to average the color values of the existing two pixels to be the color of the new pixel.

In other words, after the AB operation to get the 1;AC operation to arrive at the 2;BD to get 4;CD 5;3 is calculated by the 1245 calculation.

Note: The above is for the sake of understanding and for example, the real image operation concept and process is far more complex than this.

It can be imagined that in such a way "fabricated" pixels, and the true original pixel must be error or even a large error.

For example, the fingers of the left hand seam, the original can be very clear to see there are three dark lines, the following figure:

And after shrinking, the original finger seam part of the pixel is almost gone. With only a few light-colored pixels left, the finger seams are not clear. The following figure:

The new pixels computed with these light-colored pixels are also only likely to be light-colored and not dark. So the original dark part of the finger seam cannot be restored. The following figure:

Without dividing the fingers, the whole hand looks blurred and the image is distorted. This is why the image becomes blurred after the small dot-matrix image is enlarged.

In the actual operation in the future, do not normally enlarge the lattice map production.

Now review the second time you changed the image width to 400, the height is 226. Rather than the previous 225.

Since it is to reduce the first half, and then expand by one times, is equal to first remove 2, and then multiplied by 2, the number should be equal to the original. Why is it not equal?

This is because one of the concepts we have mentioned before, but not emphasized, is that the pixel is the smallest unit. It is no longer divisible.

The total number of pixels in an image must be an integer, and there is no 500.7 or 400.3 number with decimals.

So, the 225÷2=112.5,photoshop approximation counts as 113 pixels. Then the second enlargement, which is based on these 113, results in 226 pixels.

What we have done before, in terms of language, is to reduce the image by half, and then expand to revert to the original size. Is that right? This sentence is wrong, there are conceptual fundamental mistakes.

First, enlargement and reduction are different things, and enlargement is an operation that modifies the image. In Photoshop, the restoration refers to the undo of the previous operation and does not operate on the image itself.

As if you refuse to receive a letter from your friend, it will be returned as it is, and that is the revocation of the letter. Can be called a retreat letter.

But if you open the envelope and read it and then put it in a new envelope and send it back with a friend's address, it's a new letter, not a retreat.

Furthermore, "original" in the "original" is also wrong, through the analysis above, we know that due to the problem of taking integers, the image size and the original has been different.

The undo operation for Photoshop is described in the following sections.

Now let's outline the dot-matrix image:

Lattice format is to divide the image into several points (pixels), depending on the storage or reproduction of each point of information, so as to store or reproduce the entire picture.

Because of the limit of the number of pixels, the size of the bitmap image is fixed. Zooming in and out of the image can cause damage to the image.