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If a digital camera
or scanner image is expanded, it is made of many quadrangles. Although this quadrangle
looks square because of the screen display, it is actually a point. This
point is called a "pixel", short for picture element. The digital image is made an array
of these pixels.
In a digital camera catalog you will often see a notation like xxxx pixels x yyyy pixels. This indicates the number
of horizontal and vertical pixels photographed. |
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| By the way, since a pixel is a point, it
does not have size, but when printing, the number of pixels makes a big difference
in the final image. In a digital image, this unit is ppi (pixel per inch) or dpi (dot per inch),
and the number of the points per inch is shown. This is called resolution.
Although ppi and dpi are used interchangeably as an index of resolution, ppi
generally is used for a digital image while dpi is used when printing. |
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When adjusting the
resolution and size of a picture, you can choose whether to change the number of pixels or not. If
print size is enlarged without changing the number of pixels, resolution will be lower. Conversely,
resolution will be higher if print size is made smaller. Not changing the
number of pixels leaves the original picture as it is.You should use this method when you do not
want to lower picture quality.
On the other hand, adjustment of the size accompanied by change of the number of pixels is called "re-sampling".
This method specifies target resolution and print size. All are adjusted using the command [picture
resolution]. Since the image data capacity matches the resolution and print size, an efficient
print can be made efficiently. |
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Starting with a 3000 x 2000 pixel image,
letI?Ls change the resolution and print size without changing the pixel count.
LetI?Ls not forget that this image is about 100cm wide and 70cm high. |
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![2 Now open the [Image Resolution] command](../../images/reference/function/function01_text03_e.gif)
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From a [image] menu
chose [image resolution]. Here, since we do not want to change the number of pixels to change, uncheck
[re-sample] in the lower part of a [image resolution] screen. Then, as shown in the figure, only
the [document size] column is available. |
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Input the width and/or height,
or the desired resolution.
Here, the resolution was set to 300. Note that the "width" and "height" also change when the resolution is changed.
Here, since the resolution is changed to 300 from 72, the "width" and "height" become smaller. If "width" and "height" are
changed, of course, the "resolution" will change accordingly.
After setting the size, click the OK. |
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Although the size and resolution
were changed in [Picture resolution], the number of pixels has not changed and on a screen, there
is hardly any change. However, the actual size of the printed image has been changed. This size can
be checked with the rulers. The size is smaller. Initially, it was about 100 cm long, but now it
is only 24 cm long. Similarly, the initial height of 70 cm is now 16 cm. That is, the picture is
now compressed but it has the same number of pixels. Print quality will also increase because the
resolution is higher. |
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Adjust the size and resolution accompanied
by a change in the number of pixels. Again, for our example, a 3000 x 2000-pixel picture is used.
Please keep the display size (% display) at the top of the window in mind. This percentage indicates
the increase or decrease in the number of pixels, a reduction to 25% of the number of pixels in the
original. |
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From the [Image] menu, select
[Image resolution]. Here, since the number of pixels is changed, "Re-sample picture" at the lower
part of the screen is checked. Under these conditions, specifications in both the "Number of pixels" column
and the $B{4(Jize of document$B|(Jcolumn can be set. In addition, choose "Bicubic" with "Re-sample picture." |
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| Three types of re-sample interpolation
are possible when adjusting the number of pixels. $B?#(Jicubic$B|(Jis
the slowest method, but the most precise. $B?#(Jilinear$B|(Jis the middle resolution
and $B?/(Jearest neighbor$B|(Jis the fastest, but lowest quality. Although the processing time
increases with bicubic, higher definition is achieved. ItI?Ls best to choose "Bicubic," when
you change the number of pixels in a photograph. |
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| When re-sampling a picture, always
check $B?$(Jonstrain proportions.$B|(JIf it is checked, only one new dimension need be input.
The other dimension will be automatically calculated and the image will not be distorted. |
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When re-sampling an image, set the resolution
first and then the length or height.
Here, the resolution was set to 300 and the width and height of the “Document size” column
were input as 15 cm and 10 cm, respectively. Consequently, please note that the “Number of pixels” column
also changes. In order to change the number of pixels, not only the width and the height change, but
also the amount of image data. Here, because there are fewer pixels, the total amount of image data is
smaller.
Finally, click OK and re-sampling will begin. |
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The display of an image also changes when
the number of pixels is changed. First, look at the magnification (% of display) at the top of the
window. The percentage of the number of pixels is 25%. This means that there are fewer pixels. In
addition, this scale indicates resolution.
Resolution was 72 dpi before the change in the number of pixels; now it is 300 dpi. |
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![These supplementary functions are used during retouching.]](../../images/reference/function/menu_photo_e.jpg)
