Upcoming SlideShare
×

# Chap25

183 views

Published on

0 Likes
Statistics
Notes
• Full Name
Comment goes here.

Are you sure you want to Yes No
• Be the first to comment

• Be the first to like this

Views
Total views
183
On SlideShare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
2
0
Likes
0
Embeds 0
No embeds

No notes for slide

### Chap25

1. 1.  State the constraints between output device resolution, monitor resolution and original image.
2. 2. In This Chapter, you’ll learn on:  Identify the relationship between an image's resolution and an image's print size.  Adjust monitor and image bit depth  Resample an image based on a given print size.
3. 3. Identify the relationship between an Image’s Resolution and an Image’s Print Size Image Resolution  Resolution is the number of pixels in a linear inch— pixels per inch (or PPI), but it is most commonly referred to as dots per inch (DPI). The more pixels, or “dots,” per inch, the higher your image resolution will be.
4. 4.  With color images, each pixel can be one of 16 million different colors.  For black and white images, there are 256 gradations of gray pixels ranging from black to white: 0 (black) through 255 (white).  More pixels means higher resolution, which creates better image quality because you end up with more realistic representations of color, better gradations of both individual colors and gray tones, and crisper images in general.  The most important thing to understand about resolution is the relationship between an image’s resolution (DPI) and an image’s print size (the actual width and height).
5. 5.  These two images give some idea of the difference in quality obtained from the same size print at two different resolutions. The first one represents 360 ppi, the second 60 ppi. The latter is clearly blurred, but it is surprising how low a resolution is possible before differences are perceived by the naked eye. Generally, however, more pixels per inch mean more detail and more subtlety of color.
6. 6.  An image resolution of 200-300 ppi is quite sufficient for good output, although the optimum for most printers is 300 ppi.  An image significantly below 150 ppi begins to blur (see above) and will eventually look "pixilated" (see next page);  and resolutions above 360 ppi usually waste processor time, as the printer has to resample down.  If resampling is required it is usually better to do it in Photoshop.
7. 7.  A detail showing "pixilation". Separate pixels, the building blocks of which the image is composed, can be clearly seen. Notice the jagged, or stepped, edges apparent on curves, and the incoherent detail on the mouth of the baby.
8. 8.  Once you scan an image or take a picture with your digital camera, it becomes digitized—made up of hundreds of thousands of pixels. Pixels are nothing more than very tiny colored squares (there are 72 pixels in an inch) that you can see if you increase the magnification of any image to its maximum:
9. 9.  If you were to scan a 35mm film at an optical resolution of 2700 ppi, this will generate a file size of about 26MB.  When resizes to fit A4 paper size the image resolution drops to about 360 ppi, although the file size remains the same.  At A3 size the resolution would drop to around 240 PPI, but still gives an acceptable print.  It is possible to maintain the resolution when enlarging, by choosing the resampling option in Photoshop.  This allows the insertion of extra pixels - interpolation - by duplicating existing pixels, but can impair quality if overused.
10. 10. Resample an image based on a given print size. Resample Image refers to changing the pixel dimension (and therefore display size) of an image.  When off, allows you to change any of the dimensions or resolution options without altering the quality of the image.  When on, the computer will recalculate the pixel information when you adjust the settings, altering image quality and file size. When you down sample (or decrease the number of pixels) information is deleted from the image and when you resample up (or increase the number of pixels) new information is added based on color values of existing pixels. You specify also an interpolation method to determine how pixels are added or deleted.
11. 11. When the Resample Image box is checked, any changes you make to an image’s width or height will not change the image’s resolution, and as such, any changes you make to an image’s resolution will not affect the image’s width and height.  Keep in mind, however, when you increase width and height, or resolution, with the Resample Image box checked, you are adding pixels to your image. These pixels don’t actually exist so Photoshop must create them. As such, you will succeed only in degrading the quality of your image.
12. 12. If you want to increase an image’s width and height, or resolution, then uncheck the Resample Image box. Now any changes you make to the image’s width and height will change the image’s resolution, and vice versa:  If you decrease resolution, the width and height will increase.  If you increase resolution, the width and height will decrease.  If you increase the width or height, the resolution will decrease.  If you decrease the width or height, the resolution will increase.
13. 13. Bit Depth  A "bit" in computer language refers to the smallest amount of information that a computer can understand. It is an electronic pulse that contains one of two characters. It contains either a 1 or a 0 and can either signal on or off. Bit depth refers to the number of bits found in a graphics file or that can be displayed on a monitor.  Pixels, which make up a monitor's screen to display an image, are made up of bits. The more bits that are contained in the pixel, the greater the bit depth. The greater the bit depth, the more colors can be displayed at one time. This is also true of a graphics file. Bit depth of a graphics file indicates the amount of color in that file. As you might expect, greater bit depth brings greater file size. A 4" x 5" RGB photo (24-bit depth) will have a bigger file size than a grayscale image (8-bit depth) of the same size and resolution.
14. 14.  The best way to increase the width and height of a scanned image is to scan the image in at a high resolution (about twice what your final resolution should be), and with the Resample Image box unchecked, decrease the resolution.  Once the image width and height is where you want it, you can then check the Resample Image box and type in the resolution you want if the resolution is too high. At this point, as long as you don’t increase resolution, or width and height, your image quality will not suffer.
15. 15.  The only way to determine what your image's actual print size will be is through the Image Size dialog box or by calculating it manually from the formula (size x dpi = pixel size) i.e. print size= Pixel size divided by the resolution in dpi).
16. 16. Resample an image based on a given print size.  We have changed image size from 720x576 pixels to 360x288 pixels and as we also now have marked "Resample Image",
17. 17. • the prints size is also only half while keeping the resolution constant. So how getting the size you want without ruining the native resolution? By adjusting your print size in editor software and use PRINT size dialogs not IMAGE size dialogs.
18. 18. You should however be aware of that the width and the height of the image as you view it on your monitor is not necessarily representative of the image's actual width and height — the size it would print out at (Print Size). Average monitor resolution is 72 dpi. If you view a 72 ppi image at 100% in Photoshop, chances are that it will appear on your screen in its actual print size. However, this is not true when viewing a 300 ppi image. A 300 ppi image viewed on-screen at 100% will be enormous.
19. 19. Don't get tricked into believing that what you see on your monitor is what you'll get when you print or place the image into another application. The only way to determine what your image's actual print size will be is through the Image Size dialog box. Print size is the size of the representation of an image when it is printed. The size that it is represented on the screen is found by multiplying the size in inches by the dpi (size * dpi = pixel size). An image of 720x576 pixels that is set to 288dpi would print at 2.5x2 inches.
20. 20. While the image size and resolution have been halved the print size is still the same.