Settings and effects
There is currently no way to adjust the dot gain value of page group software and vector software, but PhotoShop image processing software can do this. The dot gain setting exists in the CMYK Settings menu item in PhotoShop 5, or in the previous version of PhotoShop, in the Printing ink settings item. The meaning of the data in the dialog box popped up by each menu item changes with the version. In PhotoShop 5, the dot gain value is lower than the previous one, depending on the built-in settings of PhotoShop. If we use the ICC Profile file during color separation, then we cannot set the dot gain rate.
If the file used is just RGB or LAB, then the change in the dot gain value has no effect on it. If the format of the file is always CMYK, then changing the value will not have any effect on the image, but the change in the value will cause the image displayed on the screen to change. Although it is the same image file, increasing the dot gain value setting will look deeper.
We cannot underestimate the accuracy of the display on the screen, because the more accurate the display, the more accurate the quality of color separation. For example, if you have two backups of an RGB file, we use a 10% dot expansion to separate one of them. Then we have an RGB file and a CMYK file. They look very similar.
Now, by increasing the dot enlargement rate to 30%, the color of the CMYK image becomes darker this time, and the RGB image does not change, so the two images no longer match.
Finally make a copy of the RGB file and convert it to a CMYK image. This new CMYK image corresponds to RGB and is much brighter than the CMYK image we obtained. If you set the dot expansion to 20%, perhaps none of the three images will match.
Which CMYK image will be better? That depends on where it is used. In the following two figures, the effect of not having one can be said to be already very good. According to the settings in PhotoShop, the magazine's dot gain value is about 18%. Assuming that the dot enlargement value on the left is too small, the image is too dark. Assuming that, like the right image, the dot gain rate is too large, it is suitable for newsprint printing rather than magazine printing.
Incorrect settings will not only darken the image, but will also have an effect on the color. And dot gain values ​​affect the midtone more than the highlight and shadow regions. In this picture, the magenta version is in the middle of the pink house and on the lawn. If the dot gain value is too small, the values ​​on the magenta version caused by the separation will be too much in these areas. It will make the house pinker, because other colors of ink cannot compete with the dominant pink. However, in the grassland area, the dominant color green was destroyed because of too much magenta. As a result, some colors were suppressed while others were emphasized. So green is very vivid in the right picture, but the pink walls are more vivid in the other.
So the most basic thing is if we know in advance the use of the image and set the dot gain rate reasonably. The results we want in this way will be similar to ours.
Even if we have to make frequent guesses about these situations, we cannot ignore its role. Maybe picture C is an error proof, but if according to the effect of this picture, another image for the magazine is to be prepared, we will increase the dot gain in Photoshop by two before the separation. Percentage.
Parrot uncertainty principle (page)
Let's take another look at the picture below. If we require the offset press to print a large area of ​​concentrated color with one or more inks, these printed inks are less likely to maintain a uniform density in this area. Generally, this phenomenon occurs when we design a uniform area of ​​at least a few inches on a page and the color of the area is overprinted by one or more solid inks. In general, this does not happen in images.
In the image of the parrot, this phenomenon has occurred. The percentage of magenta and yellow dots in the red chest of this bird is close to 100%. This actually makes a lighter portion of color than this portion get more ink than it should. In this way, the extra color renders the green area dirty.
This explains why the red area composed of magenta and yellow has a very strong color jump effect. The increase in cyan is very low. This is exactly how offset printing works. It is very likely that 3% of dot changes will occur on the same sheet of paper. So it cannot be attributed to the parrot itself.
Simply based on the situation of a single picture, it is not feasible to determine the dot gain rate. It usually takes 10-20 prints and allows the printer to do some testing on each one, preferably three times at different times of the day.
Let us look at the actual situation again. It may seem less than satisfactory to guess at the printing conditions, but it happens all the time. We don't have to worry about changing the dot gain settings of PhotoShop. We can also store the corresponding settings for any of our print conditions.
After all, the whole phenomenon is subjectively judged, and it cannot be accurately measured. Especially under some very bad conditions, the printing process is not stable. Even if the printing process is stable, what can we measure? We can print and measure a series of samples, like the industry-standard IT8, which failed because we could call it the above-mentioned reason for the parrot's uncertain rules. The presence of such large areas of thick colors can cause changes in printing conditions and invalidate the testing process.
Actually, what kind of version of PhotoShop are we using in our work? Do we understand what they mean by the expanded dot value? It doesn’t matter why dot gain is important. It’s important that we must know if the print looks like Too dark, you need to increase the setting of the dot gain value. If it looks too bright, you need to reduce this value. This method looks clumsy and the result is actually very stable.
Therefore, at the time of this magazine's production, we have basically grasped the dot enlargement rate of the printing process, so the F-picture published by this magazine looks almost the same as the calculation screen. Picture D, because it is the same as the device used in F-picture, the result is very similar to it.
The darker picture of A is due to the use of more sophisticated screens. The B chart is slightly brighter because it uses the direct plate making method. These two are things that the results should be expected. In this special case, copying realistic colors is not a problem. If there is a problem, it sets out the dot gain value before it is made. In this way, before seeing proofs, we can estimate the printed proofs.
The production of printed documents is always an uncertain guessing process. Understanding the settings of outlet expansion and adjusting it according to printing conditions is a good way to improve the production process of such printed documents.
Source: Innovative Graphic Arts