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Scanning Techniques CPE 2003 seminar

CPE Show Seminar – Saturday November 4, 2000
Topic – Scanning techniques and Image manipulation in PhotoPaint and Photoshop
What will be covered:
1. What is the optimal scanning resolution (dpi)
2. What is the optimal file size (inches) to work with
3. Working with Brightness and Contrast in your scanner
4. What is RGB? What is CYMK?
5. Optimal Tools to Work with – Levels and Tonal

What is the optimal scanning resolution?


Resolution Reference Charts
These charts show the relationship between image size, file size and resolution. Resolution in the computer can be confusing because it’s not a constant. You have to think in terms of the amount of information stored, which is why it’s often helpful to compare file sizes rather than resolution. Use these charts to help in your scanning, filing and output decision. Numbers have been rounded off for ease of understanding
Different scan resolution, different original sizes, same size files:
Original (Inches) Scan Resolution File Size
8 by 10 300 dpi 24.8 MB
4 by 6 600 dpi 24.8 MB
1 by 1.5 (35mm) 2400 dpi 24.8MB
Same scan resolution, different file and images:
Original (Inches) Scan Resolution File Size
8 by 10 300 dpi 24.8 MB
4 by 6 300 dpi 8.4 MB
1 by 1.5 (35mm) 300 dpi 0.4 MB (400kb)
Resolution is measured, for the most part, in dots per inch (dpi). This is an actual physical measurement, but it can get a bit difficult to visualize when dealing with such tiny measurements. Still a little confused? Well let’s use a more realistic example. Resolution or dots are for the most part like small balls covering a field. So you can think of a photo in the same way. Each image in is composed of small lines or golf balls all lined up in a row.
Output Resolution and Printer Resolution
The best place to start for a thorough understanding of resolution is in the output stage. On most scanners, you will find an input box where you can plug in your planned output resolution – see figure 1. Set this number to 300 dpi. See figure # 1. (The designation dpi is slightly deceptive here -it is really pixels per inch or ppi. It is typical now, though, to refer to it as dpi) There’s a simple reason why we set the scanner to 300 dpi – your printer is optimized to print its best quality colour at 300 dpi. So we set the scanner to match the printer.
Output decisions have to be made on the basis of image size and the  resolution need of the printer (200 -300 dpi), the web (72 dpi) or other end use that you are using. Note (*): Print size is usually stated with the smaller number first, while pixel size is usually given with larger number first. The charts here show the smaller number first simply to keep the order the same though out the example.
Different dpi and image size, same pixel dimensions, same file size:
Dpi Size (Inches)* Size (Pixels)* File Size
2400 dpi 1 by 1.5 (35mm) 2400 by 3600 24.8 MB
300 dpi 8 by 12 2400 by 3600 24.8 MB
150 dpi 16 by 24 2400 by 3600 24.8 MB
72 dpi 33 by 50 2400 by 3600 24.8 MB
Same dpi or image size, different pixel dimensions and file size:
Dpi Size (Inches)* Size (Pixels)* File Size
300 dpi 8 by 12 2400 by 3600 24.8 MB
72 dpi 8 by 12 580 by 860 1.42 MB
300 dpi 4.7 by 7 1400 by 2100 8.43 MB
300 dpi 4 by 6 1200 by 1800 6.2 MB
300 dpi 3.3 by 5 1000 by 1500 4.3 MB
When you look at the printer’s spec sheet, it may say that it’s a 600-dpi printer or an even higher resolution. Don’t be fooled into setting your output resolution to 600 dpi, though. Printer resolutions are related to image resolution, but the numbers mean different things. Output resolution from you computer is a matter of pixels, and printer (laser or inkjet) resolution is a matter of dots. Your printer’s maximum resolution may be 600 dpi, but remember that pixels are bigger than dots. Many dots are set down by the printer to create the physical manifestation of a pixel. Even if you set your output resolution below 300 dpi, your printer, set on highest quality, will still be laying down 600 dpi. For example Epson states that it takes approximately 3 dots to equal a pixel.
Your printer is made to print colour at a maximum output resolution of 300 dpi. If you don’t believe it, try printing an image at 300 dpi, then something higher, say 600 dpi. You won’t see any difference. The printer doesn’t need any more information than 300 dpi. I bet you if you print out at 200 dpi you will not see a difference. If you check out some dye-sublimation prints at 300 dpi you’ll soon see that it’s difficult to imagine getting any finer than that.
The other things that happen if you change your output resolution beyond 300 dpi are that either your file size balloons or your image size diminishes greatly, depending on whether or not your computer is set to resample your image. Remember that image files are large enough to begin with, and plugging in higher output resolutions is a drain on both your system Ram and Hard drive resources. It serves no purpose and only increases the “hair pulling – hourglass wait state”.
* Note: If you think you are going to need the image later on or you do not know what your final artwork is going to be you could save it as a 600 dpi image, for example, which means that you can safely increase the size by 2 times.
Thus, in sublimation you should be scanning your image in at 200 to 300 dpi. We still need one more variable filled in. Point 2 takes care of that.

What is the optimal file size (inches) to work with?


The optimal file size in inches would be the size that you want the final image to be. If your image is to be 4 inches on a plaque than make it 4 inches in your scanner software. Most scanning software allows you to resize the image in the final output of the scan. See figure number 2.

Brightness Contrast


Sometimes when you are scanning an image – especially one that has an image on a white background, you will get a light gray background where your white image should be. To compensate for this you could adjust your brightness or contrast to light or darken or lighten up the background. Play around with these settings to get a better feel of the controls. See figure – 3



RGB – CorelDraw’s RGB mode uses the RGB model, assigning an intensity value to each pixel ranging from 0 (black) to 255 (white) for each of the RGB components in a color image. For example, a bright red color might have an R value of 246, a G value of 20, and a B value of 50. When the values of all three components are equal, the result is a shade of gray. When the value of all components is 255, the result is pure white; when the value is 0, pure black.
RGB images use three colors to reproduce up to 16.7 million colors on-screen. RGB images are three-channel images, so they contain 24 (8 x 3) bits per pixel. RGB is the default mode for new CorelDraw images. Computer monitors always display colors using the RGB model. This means that when working in color modes other than RGB, such as CMYK, CorelDraw temporarily converts data into RGB data for display on-screen.
You should always work in RGB when you are working with your image in Corel Photo Paint or CorelDraw.



CYMK – The CMYK model is based on the light-absorbing quality of ink printed on paper. As white light strikes translucent inks, part of the spectrum is absorbed and part is reflected back to your eyes.
In theory, pure cyan (C), magenta (M), and yellow (Y) pigments should combine to absorb all color and produce black. For this reason these colors are called subtractive colors. Because all printing inks contain some impurities, these three inks actually produce a muddy brown and must be combined with black (K) ink to produce a true black. (K is used instead of B to avoid confusion with blue.) Combining these inks to reproduce color is called four-color process printing.
The subtractive (CMY) and additive (RGB) colors are complementary colors. Each pair of subtractive colors creates an additive color, and vice versa.
Your printer converts your RGB values into CMYK values. It is not advisable to work in CMYK, as your ink printer will convert back to RGB and then into CMYK.

Levels and Tonal Equalization Level Equalization


The Level Equalization filter (figure 7) lets you change shadow, midtone, and highlighted areas by redistributing shades from darkest to lightest. Level equalization lets you preserve shadow and highlight detail that is lost when you adjust the brightness, contrast, and intensity of the tone of an image. You can also use the Level Equalization filter to create color gradations on posterized images; to lighten or darken any combination of shadows, midtones, or highlights; to compress brightness values to printable limits; and to adjust the gamma curve (midtones).

Adjust Your Levels


Adjust your levels to make the image darker or lighter

The Tonal Curve


The Tone Curve (Figure 9) filter lets you perform color corrections precisely by controlling individual pixel values. You can pinpoint a problem area and produce a subtle or pronounced change in that area, which dissipates according to the tone curve as you move away from the targeted area. The Tone Curve filter lets you take current pixel brightness values as input and change them to different values. The response curve represents the balance between shadows, midtones, and highlights.


Handy Scanner Check List

Scanner Specs
1. Make sure the scanner you buy has at least a 24-bit colour depth.
2. Make sure it has at least a 300 by 600 Optical (not interpolated) resolution
3. It should have at least an 8.5 by 11.5 bed size
4. It is best to have a scanner that comes with a SCSI card or a USB connector (If your computer supports USB buy this type – it is easy and does not require opening up your case). You can also purchase a parallel version which connects to your parallel port (printer port). This type of connection is the slowest of the three. The SCSI and the USB are the fastest. However, there is nothing wrong with the parallel interface. If you have a parallel scanner you will need to attach your printer into the scanner. The scanner comes with a parallel pass through port so don’t worry if you think you will not be able to run your printer.
5. Keep the glass clean. Do not scratch it.
6. Make sure you turn the power off to the scanner when you are not using the scanner. Most newer scanners come with a power saver mode and will “sleep” when not in use for a certain time limit.
7. My choice for a scanner is the HP 5300C(supports both USB and parallel) or 6300C(USB and comes with an optional document feeder). Don’t be fooled by the $99 dollar scanner.
8. For more tips on scanners check out this site from HP They produce a newsletter also.

Quick tips for Better Prints


1. Buy a good scanner – not a $99 one.
2. Buy a good Monitor and Graphics card.
3. Scan at a resolution that will give you the image size you want to print at an output resolution of 300 dpi.
4. Your printer is typically optimized to print colour at 300 dpi. Scan so that the image size you want will be printed when your output resolution is set to 300 dpi. If you are running low on ram or disk space, scan so your output resolution will be 200 dpi – the prints will still be acceptable. Even for colour prints.
5. Experiment with colour correction. Don’t be afraid to experiment with your image. Play with the curves, levels, saturation, brightness and contrast. You can always save a copy, so nothing is irreversible. If you have a good scanner and monitor this will really help how your image will look on your final output.
6. For best results run a calibration of your scanner, software and monitor. This will help get rid of “what looks one way on my scanner does not look like on my printer.”
7. Run your monitor at 24 bit high colour. This will supply you with good colour depth.
8. Run your screen resolution at a minimum 800 by 600. See article on screen resolution.
9. Don’t attempt software interpolation to increase your image size for printing. Get the size of the image when you scan it. If you need the image to be 3 inches scan at 3 inches. Printing your image at the size you scanned will give you the sharpest picture.
10. Do a test print on cheaper media. This is a great way to check for any imperfections that you may not see on the screen.
11. Print on high quality medium. The end result is only as good as the medium you put it on. If you are doing sublimation, then you need to use the genuine sublimation material. This will give the best results.
12. Use a good photo program such as Adobe PhotoShop or Corel Photo Paint
13. And finally buy a good ink jet printer. Say the Epson 900,740 or comparable models from HP or Canon.

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