Resizing Images - From PHOTOS to ART with Photoshop - page 59

the image, I still have enough pixels available in my image file to print at a resolution of
396 pixels per inch. If I want to print at a resolution of 300 pixels per inch, Photoshop will
have to discard some of my pixels. An 8X10 image at 300 pixels per inch (ppi) only re-
quires 8X300X10X300 or 7.2 Megapixels.
In this example, Photoshop has discarded more than half of the pixels that were in the
original image file — first, because of cropping, and secondly from reducing the resolu-
tion to 300 ppi. My file size was permanently reduced from 15 Megapixels down to 7.2
Megapixels. These lost pixels cannot be recovered.
If on the other hand, I want to print at a size larger than 15.84 X 10.56, Photoshop will
have to create additional pixels for me. So let's say I want to print a 30 X 20 image. Pho-
toshop will tell me that I only have enough pixels to print that image at a resolution of 158.4
pixels per inch. Although I can print at that resolution, it will be noticeably comprom-
ised. A better solution is to have Photoshop create new pixels to enhance the image. It
does this by sampling the color and tone of pixels surrounding each pixel it needs to create
in order to provide pixels that blend with their surrounding pixels. This process is called
RESAMPLING and Photoshop will do it automatically if the Resampling Box is checked.
End of Math Explanation!
============================================================
Bottom Line: If you need to change the resolution for a given size image, Photoshop
will “Resample” your image. If the resolution is reduced, pixels will be permanently dis-
carded. On the other hand, if the resolution needs to be increased, Photoshop will create
new pixels to achieve the desired result. This process is not reversible.
Note in Figure 24 that I have a 43.1 Megabyte image file. An image file records three
bytes of information for each pixel in the image — Red, Green, and Blue values. Since
I have a 15-Megapixel image and three bytes for each pixel, I should expect an image in
the range of 45 million bytes or 45 MB. The actual value is 43.1 MB because of other
factors beyond the scope of this topic. I mention this because many people think that a
15-Megapixel camera will produce a 15 MB image file. The actual file size of images pro-
duced by any camera depends on a number of factors that are beyond the scope of this topic
and is never a direct relationship to pixels.
Figure 25 should further enhance your understanding of the Image Size Window. As you
can see in Figure 25 , there are six drop-down menus in the Image Size Window. In most
cases, the default settings will be your best bet. The one exception is the drop-down menu
next to the Resampling Box. It has additional options that are optimized for enlarging and