The scanner can be used to scan colorful and colorful images and texts. Its applications range from family to professional printing.
With the popularization and development of computers, color printing systems have mushroomed and have been widely used in various fields such as advertising, light printing, newspapers, publishing, and even households. As an advanced computer's image input device - flatbed scanner, it has reached a level of purity and love. Nowadays, digital imaging devices such as scanners have become one of the indispensable external devices for computers. In the application of image systems, more than 70% of input images are input using flat panel scanners. In the increasingly widespread use of flatbed scanners, how to identify the quality of the scanned image is very important.
In order to judge the quality of scanned images correctly, first, check your originals and you must use a good quality original for scanning. Because the scanned image is always better than the quality of the original (in the case of a basic preset scan). Therefore, if your original is of poor quality, use the many functions provided by ScanWizard software to correct the original image.
Second, you must correct your system based on information provided by vendors (such as monitors and printers). If you use a CMS (Color Management System), make sure that it is under the correct correction conditions, or at least you should follow The instructions for correcting the display in the Adobe Photoshop user manual are used to correctly display the scanned image because a good display and full color display card are necessary for checking the quality of the scanned image.
First, check the tone range
Check the highlights and shadows to see if there are enough fine levels. If not, the highlights and shadows will appear as white or black with the same value, or the value will change very little. Using Photoshop's "Level" or "Histogram" can help you check the condition of the scanned image, and also check whether the continuous level changes smoothly from bright to dark or shows a band gap if there is a clear band. Gap, your scanner density range is low.
Second, check the color
Check if the color of the scanned image is balanced, or check the image for color cast. The easiest way to check the color balance is to check the neutral gray and see if there is a color cast, or check the color of the impression (such as the color of the fruit, sky, grass and flowers) to see if any of the colors are unnatural; check the saturation of the scanned image The degree is good enough, compared with the original is too dark or too bright. We can use image processing software to correct color balance and saturation.
Third, check the clarity
If the scanned image has an unclear focal length, the scanner may have a problem. It may be that the vibration during the scan is too great, and perhaps the registration is too bad. Images scanned by a good scanner should have sufficient sharpness to get good detail (at least in the midtone part). However, the CCD scanner still does not reach the definition of the drum scanner compared to the drum scanner because there is a virtual light mask function (completed by hardware) in the drum scanner, and in the CCD scanner, There is no such hardware to perform the dummy mask function.
Fourth, check the brightness
By comparing with the original, whether the scanned image is too dark or too bright, too dark or too bright is not a good scanned image. Adjusting the gamma value brightens the dark image, but it causes the scanned image to lose information. Therefore, a good scanned image should have the correct light meal, and the user does not have to make too many adjustments. In fact, to tell whether a scanned image is good or bad is not a sham and simple work, because it requires the user to understand the basics of color and scanner. However, in some cases, good and bad, the user is still very easy to judge, the easiest way is to compare the scanned image with your scanned manuscript, but this is also controversial because of your display status and ambient brightness Conditions may lead you to make wrong judgments.
Therefore, try to read the color value on the scanned image to see if it is close to the color value of the original, and it is best to perform it in the CMYK mode.
It should be emphasized here that most of the current platform CCD scanners use the RGB mode to scan. If a good RGB image is converted to a poor CMYK image, it is not the cause of the scan, but due to the poor conversion. This is an industry issue that needs further discussion. In short, the quality of the scanned image directly affects the output quality, and the image quality is related to the optical resolution of the scanner. Therefore, a scanner with a higher optical resolution must be selected so that the scanning can achieve clear gradation, vivid colors, and vivid vividness. Satisfactory image effect.
In a workflow that includes color management, we can precisely control the color from the capture of the image to the digital proofing process; however, if the original itself is somewhat color cast, it needs to be corrected in Adobe Photoshop. This article presents two examples demonstrating accurate color correction techniques. The advantage of editing images in the RGB color space is that neutral reds are obtained after equal amounts of red, green, and blue primary colors are mixed. We can see how the RGB color space works in ColorMatch and AdobeRGB.
Adjustment of the curve with Colorsamplertool
In Photoshop 5.0 and later, color sampling tools can be used in combination with the Info panel to obtain accurate, measurable color corrections in RGB images. First, click on the Window menu and select “ShowOption†from the drop-down menu. The “Option†panel strip will pop up. Select the sampling area from the PointSample drop-down list, such as 3×3 or 5×5 pixels. PointSample is usually not useful because it only calculates the value of a pixel. The area of ​​a pixel is too small. The resulting color value is not accurate. The color value we want is not the value of the scanned pixel. It's really representative sampling color values.
Open a .jpg image and select the "ColorSamplerEyedropper" tool from the toolbox. Click on the image and select four color samples from the highlight, midtone, and shadow sections. The selected color point is surrounded by a small bullseye, and each point appears on the Info panel. The color value. We can calculate the adjustment curve based on these values ​​and use this curve to correct the color cast of the image.
Click on Image and select the Curves command under Adjust from the drop-down menu. This will bring up the dialog for the dialog box. To place a point on the curve, just click anywhere on the curve. You can click the mouse; if you want to add a point that you want to base on a specific tone on the image, you can click the cmd (Mac) or ctrl (PC) key while clicking on a point in the image. The mark changes to a crosshair and the point is added to the corresponding position of the curve. In this example, the four color sample points previously taken should be added to each color channel curve.
This process is not as difficult as described. The cursor and the sample cross are coincident. Press the cmd (Mac) or ctrl (PC) key and click the mouse to see the RGB curve. The corresponding point.
Now let's analyze the sample readings on the Info panel to see how the image's color cast is corrected. Assume that the image we choose is a neutral gray image. The color values ​​of the RGB primary colors in the highlight, midtone, and shadow regions of the image should be substantially equal.
Let's start with the midpoint sample 2 and hope that the red and blue color values ​​match the green color values.
Remember, we have added the corresponding sample points in each channel, open the “Channel†pull-down menu at the top of the curve dialog box and select each channel individually. Click on the spot on the image to see which channel on the selected point the point is surrounded by a circle. Select a point with the mouse to modify it, there are two ways to modify, or click and drag with the mouse, or use the arrow keys on the keyboard to move the point on the curve up and down. You can also enter new values ​​in the "Output" field in the lower part of the dialog box so that the three color values ​​are essentially equal. Each channel is operated in this way, and each sample point is also operated in the same way, so that the color cast correction can be completed.
Load this curve's settings into the Load Curve dialog box. This curve can then be used in the same application.
Hue/Saturation
Below we describe a method for locating a color in an image and changing its hue. This method does not require complicated selection. Open a picture with a yellow pattern, use the Hue/Saturation tool to change the yellow of the pattern, select Adjust from the Image drop-down menu, and then select the Hue/Saturation command to open Hue ( Hue) / Saturation dialog box, in this dialog box we can determine a particular range of colors, from the Edit drop-down menu in the upper part of the dialog box, select the yellow, then at the bottom of the dialog two Two sliders appear between the color bands, the upper color bar does not change, representing the hue of the input color; the lower color bar represents the hue of the output color and shows the relationship with the input color. We can drag the slider to a new position and change the color range. The color range is affected by other parameters in the dialog box. In addition to the Master mode, other color modes can be directly sampled in the image, and the slider moves accordingly to the selected color.
Use the Hue/Saturation filter to locate a narrower color range, that is, move the two sliders to very close positions. Changing these values ​​changes the value of the corresponding color in the image accordingly.
Reprinted from: Hongn Online