Scanner scanning color negative method

Color negatives are difficult to scan, first because they have a particularly small density range, about only about 2.0, so that after conversion into a positive image becomes plain and unpredictable; second, because its color and image are reversed, it is difficult to imagine how Adjust the exposure or filter curve to correct color cast.

Because the density is relatively small, the flexibility to adjust the exposure is rather large. For flat panel scanners with low signal-to-noise ratio in low light, we should first adjust the exposure so that the scanned image is as bright as possible. If possible, make each color component at or near 255 while adjusting the output Y value or the steepness of the curve as much as possible. As shown in Fig. 1, the scanned negative image is fully displayed in the brightness range of 0 to 255. In photoshop, the scan result is converted into a positive image to see the color cast to adjust the exposure, and the white neutral gray is generally used to check the original. How partial RGB components are equal. At this time, if the blue color should increase the blue exposure, instead of reducing the exposure as if it were scanned.

After these adjustments, we can get the image of Fig. 3 and examine its brightest and darkest points. It can be seen that its data has been expanded in the 0-255 space as much as possible.

Then reverse the display to check for serious color casts. If normal, use photoshop's reverse function to turn it into a positive image (Figure 4). It can be seen that the colors of the images obtained after the reversal are not ideal, mainly because of the low contrast and insufficient color saturation. Use photoshop's curve adjustment function to make adjustments, adjust the curve to concave, increase contrast and color saturation (see Figure 4). If you are not satisfied with the color of the image, you can also adjust the RGB curve separately. Finally, the result shown in Figure 5 is obtained.

The picture obtained by scanning with a negative film cannot be compared with the original film, so the possibility of failure is still relatively high; furthermore, the calculation of negative rotation is not ideal. So unless you have to, you should still enlarge the negative film and then scan it.

It should be noted that the color calibration curve in the scanner is very different from the school color curve in photoshop. Generally, the scanner has 10 to 12 bits of information after the exposure is converted to voltage, and the color correction curve in photoshop has only 8 bits of information per color. Therefore, when converting the scanned data to an image file, some of the information is lost. Data, we must pay attention to this point in the use of the process.

Source: Printed Today