Digital Camera Electronic Imaging Technology and Its Impact on the Prepress Industry (4)

2. RGBE filter

Recognize the basic principle of RGBE filter color, mainly from the fourth color E (Emerald, Emerald) start.
In the study of human eye color, people obtained the sensitivity curve of the eye to different wavelengths of visible light. This sensitivity curve is divided into three kinds of red, green, and blue, colorimetrically expressed as,,. In the red curve, there are two sensitive peaks, one in the red zone and the other in the cyan zone. This just shows that the human eye does indeed have a cyan portion of the sensitive properties of shade, which is not available and can not be reflected in the general red filter (see Figure 7).

Using emerald green filters to compensate for this defect makes the digital camera's color perception characteristics closer to those of the human eye. This is indeed a good idea. When the emerald color filter is added, colors that cannot be “feeled” or cannot be “feeled” correctly can be correctly reproduced, showing an extension of the excellent domain. After obtaining the four color signals of RGBE with larger color gamut, you can convert it to a RGB system with a larger color gamut (note that the number of colors that different RGB color spaces can represent is not the same). Excellent digital color image. It can be seen from FIG. 8 that in the color image captured by the RGBE system, the blue-green color of the dark blue can only be correctly reproduced under the general color gamut RGB filter system.

Sixth, the impact of digital camera technology development on the prepress field

For the prepress industry, digital cameras are mainly used for the acquisition of image information. When the digital camera’s technical capabilities are still relatively weak—the resolution, color, and quality of the layers are not high enough, most of the image input in the prepress area comes from scanning the original. With the advancement of the aforementioned technologies, digital cameras have been able to meet the pre-press processing requirements to a large extent. Therefore, the use of digital cameras to produce “digital manuscripts” is gradually becoming a trend in the prepress industry.

The advantage of the digital camera for image input is that it avoids loss of image quality during photography, development processing, and image scanning of the photosensitive material, and the acquired image is a “original digital information” that is directly acquired. At the same time, it is conducive to the complete digitization of the replication process. At present, the disadvantage is that the resolution (number of pixels) is still insufficient for large-format image copying, and its resolution, color, tone level, dynamic range, etc. are higher than those of high-quality color reversal films. There is still a slight gap.

We may wish to analyze several common pixel-level digital cameras and calculate the size of the images that can be printed and copied for comparison with scanned images for print reproduction.

The calculation is based on the scan resolution formula:

Scan Resolution = Quality Factor × Magnification of Image Side Length × Screen Number of Lines, where Quality Factor = 1.5 ~ 2.0

Rewrite the above formula as:

Image Resolution=Quality Factor×(print side length/original side length)×Cable Screen Number: image resolution×original side length=quality coefficient×(print side length)×screen number of lines of image pixels=quality coefficient× Print side length × number of screens

Get: According to this formula, calculate the number of 14 million, 8 million, 6 million, 5 million, 4 million, 3 million pixels and other digital cameras respectively, the number of printing screens used is 100 lines per inch (newspaper) and 175 lines/inch (higher quality prints), quality coefficients of 2.0 and 1.5, respectively. The results are shown in Table 1.


From the data in Table 1, it can be seen that the digital camera is fully capable of capturing newspaper images. Digital cameras ranging from 3 million to 14 million pixels can print and copy image sizes ranging from 16 to off. For high-quality, 175-line/inch printed image reproductions, digital cameras of 3 to 4 million pixels can meet the image reproduction requirements of about 32K; images taken by digital cameras of 5 to 6 million pixels can satisfy 16 Open the left and right image copy; 14 million pixel digital camera can copy 8 or so images.

If a 6cm x 7cm color reversal film is used as a manuscript, it is magnified to 10 times the original size, and a large-format print of 60cm x 70cm is produced. The print resolution is 1.5 x 175 lines/inch. 10 × 175 = 2625 dpi, the number of pixels is 7234 × 6200, about 44.85 million. At present, digital cameras cannot achieve such a high resolution. According to the resolution of the color reversal film (approximately 100 lines/mm, which is equivalent to a scanning resolution of not less than 5080dpi), it is still feasible to adopt higher resolution scanning, which can be seen in large-scale, high-quality high-end fields. Film originals still occupy a more stable position.

However, it is believed that the continuous development of electronic imaging technology will continue to promote the technological advancement of digital cameras and contribute to the digitalization of image information and the development of digital prepress.

Source: Ke Yin Network