As already mentioned, perfect transparent digital negatives do not exist. For example, the quality of the correction is affected by the paper’s quality, whether it is smooth or rough, whether it has a uniform structure, whether it is evenly whitened, and so on. To a large extent, the quality of negatives’ production depends on the accuracy of measuring devices, such as a scanner, camera, or spectrophotometer.
But the quality of application of light-sensitive solutions on paper has the most significant effect on the results of corrections. And to overcome these problems and at the same time to make fans of alternative photography aware of this problem, I added to the EDN program, the module that shows the quality of the coating.
What do we need?
To test the coating, we need the EDN program (1), which can be run from www.EasyDigitalNegatives.com via the Run > EDN 2.2 command.
We can also download the program from the same web address and run it from our home computer. In this case, we extract the program to a folder and double-click the index.html file.
To create a sample, we need the file EDN_COATING.tif (2), located on the mentioned website in the Downloads menu. This file does not need to be mirrored and inverted before printing, as the image on a transparent film is virtually transparent (2).
When we place this transparent negative on paper, and the image is printed, a positive image (3) is obtained. Due to the transparent surface, the image shows a surface with theoretically equal dark squares.
When we drop the scanned sample to the Choose File button (4), the program read each square’s value.
The result is shown in the graph section as a jagged line (5). The value of the first square in the sample is shown in the line’s leftmost part (5).
Namely, the EDN program starts reading data from the upper right corner of the sample towards the extreme left square, and then gradually moves to the bottom of the table (6).
The graphic display of the quality of the coating also contains information on the quality of the coating. If the deviation on the coated surface is less than 3%, the coating is excellent. However, due to the deviations mentioned above, such a high-quality coating can hardly be achieved.
A coating in which the color values deviate by 3 to 5% is marked as a good coating. We will achieve this with some practice.
A coating with a 5 percent or more deviation signifies a rather poor application of a light-sensitive solution. With such an application, making negative corrections will be quite unreliable, so it is better to improve the technique of applying solutions.
But when learning to apply solutions, we need to be rational, as excellent results are unnecessary and almost impossible to achieve. The advantage of the EDN program over other programs is that it can calculate the average of the read values. When calculating the average using a more significant number of samples, the program removes larger deviations. That, in turn, leads to much more precise corrections. In our example below, for example, we obtained one bad and two good results in measuring the samples. Due to the calculated average or removal of deviations, the coating result is excellent (7). EDN displays another exciting piece of information. In the case of opening a single sample, the program displays information about the approximate maximum color density (D-max) on the sample. When opening a large number of samples, the program displays the inscription multi.
Quality control procedure
As we have already described checking the quality of the coating, we will not mention it again. Maybe the only thing that matters is that we need to print the sample file correctly. That means that it must be of the correct size and resolution and that the caption Easy Digital Negatives is placed in the upper left corner of the image (8). If an image is inserted incorrectly in Easy Digital Negatives, the program will treat the sample image as a step wedge table, and it will calculate the correction curve.
Results of quality
The first surprise we experience when we check the quality of coating on a paper is a more or less jagged line showing the table’s color values (9).
Theoretically, this line should be perfectly straight, as all squares’ color values should be the same. But in practice, due to the various factors mentioned above, squares cannot have the same values. Surprisingly, in our case, the color deviation is almost 12%, which is unacceptable. If we want to calculate perfect corrections for a transparent digital negative, the deviation must be much smaller.
Results of incorrect application
In the following paragraphs, we will look at some basic results or errors deduced from the coating quality curves.
The most common form of visible result observed in photographic beginners is the so-called sawtooth wave. The color data, in this case, slowly rises and then falls sharply, or it rises sharply and falls slowly (10).
Such a curve indicates that we applied much more solution to one side of the paper (left or right) than the opposite side. If we show a slightly exaggerated example, we created a kind of gradient due to the stronger (or weaker) pressing of the brush or glass rod towards one side of the paper (11).
This uneven application is almost invisible to the naked eye, but the computer recognizes it without significant problems. In our case, the program first notices a rather bright tone (12). Then, the squares’ values in the table become darker as we move towards the left side of the paper (13). Next, the program jumps to a new, lower row of the table, and here again, encounters a lighter tone (14). And so on, until it reads all 16 lines on the sample, creating on the curve 16 characteristic peaks (11).
Of course, the solution to the problem is in a more even application of the solution in all directions.
Falling or rising values
The following result is due to the same error as in the example above. But now, we applied too much solution, not to the left or right part of the paper, but the upper or lower area of the paper (15).
As mentioned, the left part of the graph shows the data in the upper rows of the printed sample (16), and the right part of the graph shows the data in the lower rows of the table (17). Therefore, the upper part of our table is almost 12% lighter than the lower part of the sample table (18). Now that we know some facts about the graph, we can briefly show a few more examples of errors.
Drying on clothesline
The curve (19) presented below shows the color values when drying paper on a clothesline. We pinned it to one corner (20).
We can see a combination of sawtooth wave and descending values. The upper left part of the paper is lighter, as the solution slowly drained into the lower, right, now darker part of the paper.
A puddle on paper
If a puddle of light-sensitive solution (21) forms on the surface of the paper, this is shown in the graph with a smaller area of darker values (22).
Lines on paper
Much more rarely, we will observe a seemingly chaotic distribution of values in the graph (23).
That is a sign of an inferior technique of applying light-sensitive solutions. In our case, we did not apply enough solution to the paper. Bright brush marks formed on the surface of the paper. All these problems can be easily solved with an improved coating technique, which will also affect the production of a much better correction curve.
The quality of the correction of a transparent negative is not only influenced by the coating technique. When using cheaper printers, we will also notice deviations in printing.
We can check the printing quality by printing the inverted and mirrored EDN_COATING.tif file on photo paper. In this way, we get a positive picture (24).
When the image is scanned, cropped, and dropped into the program, the result is better than in the manual coating. But with inaccurate printing, we will see that the measured values will increase (25).
The colors on the printed sample become brighter towards the bottom of the paper. The line is rising.
In such a case, if we turn the sample 180 degrees upside down, the results are also reversed. Most of the light tones are now on the left side of the graph (26).
And because we know that the program checks the printed areas from right to left and from top to bottom, the data shown tells us that the printer at the beginning of the paper starts printing with the darker color, which gradually became lighter (27).
Since the program showed a 3% deviation in the printed sample, we can assume that the printer prints 3% brighter at the end of the sample than at the beginning.
If we now lighten the inverted and mirrored EDN_COATING.tif file (27) in a photo editing program with a 3% gradient, we will get an ideal data after printing the corrected photo.
A big problem in making digital negatives is also photographing the sample from which we want to read the data.
In the case of uneven lighting of the sample, the results will be significantly distorted.
We can check the scene lighting quality by first printing the inverted and mirrored EDN_COATING.tif file (24). The sample is then photographed four times, rotating the image 90 degrees each time.
If the graph results are different each time (15 and 19), the illumination of the sample is uneven. In this case, we can correct the scene’s lighting, but we can also correct the photographed sample by adding the appropriate gradient in any digital photo processing program.
It is impossible to produce high-quality transparent digital negatives if we do not know how to apply a light-sensitive solution to the paper properly. The Easy Digital Negatives program has a built-in coating quality control module, which can detect our coatings’ quality.
- From the Internet, we download the file, EDN_COATING.tif.
- The file is NOT mirrored or inverted; it is simply printed on transparent film. Print settings are not relevant, as we only check the quality of the coating.
- The file is printed with the approximate exposure time.
- The photo is developed and dried. Once the sample is dry, it is scanned or photographed.
- If we have photographed a sample, we need to assign the right size and resolution to the digital image of the sample.
- We load the digitized image in the EDN program. The program displays the coating quality in the program graph.
- The coating is practiced until the coating curve becomes almost flat.
About coating quality
Easy Digital Negatives has a built-in module that allows us to check the quality of coatings on a positive image. A high-quality transparent negative cannot be produced if the light-sensitive solution is applied unevenly to the surface of paper or any other material.
Instead of an approximately straight curve, we see jagged results, which significantly distorts the calculation of corrections (1).
This module’s essence is that the users became aware of the quality of their coatings and, and, if necessary, perfects the application technique.
When we load a positive image of the sample produced with an EDN_COATING.tif file in the Easy Digital Negatives program, the module’s operation is triggered automatically.
The quality of the coating is displayed in the graph window (2) and described by a simple description (3).
Graphical representations of incorrect coating (4) are described in the following instructions.
Checking the quality
1. Downloading a sample step wedge file
1. We open an internet site www.EasyDigitalNegatives.com.
2. In the Downloads menu, we find the file EDN_COATING.tif (1).
3. We right-click on the file name and download the file to our home computer.
2. Printing a sample file
1. The printing process is quite simple. We open the EDN_COATING.tif file in the photo editing program.
2. We do not change the image in any way, as it is ready for printing.
3. There is no need to change or use any printer settings to print this file, as the final negative is essentially wholly transparent.
4. We load transparent film into the printer and select file> Print command.
5. Once the photo is printed, we wait about an hour for the ink on the transparent film to dry completely.
3. Exposure time and printing
The exposure time is not essential when printing this file, as the program only checks the uniformity of the coating on the paper. But, it is still better to use printing time when the image will be too dark rather than too bright.
We place the negative on the paper so that Easy Digital Images (4) is correctly inverted on the positive image. Therefore, the negative is placed on the paper so that the transparent film emulsion faces the paper (2).
4. Making a positive image
Once the sample is exposed, developed, and dried, it is scanned or photographed. We will present only scanning using Mac’s Image Capture program, although the settings will be similar to other scanning programs. The scanning technique described below is, therefore, generically useful for most scanners and adapted to the rapid achievement of results on all kinds of scanners.
1. We place the image of the sample in the scanner, but before scanning, we adjust some settings (3).
2. First, we select color scanning with 24-bit depth or millions of colors.
3. If there is an option, we select the best scanning quality.
4. The optimal scanning resolution of our samples is 300 dpi.
5. Then we choose the Color scanning or sRGB color space.
6. In the next step, we click on the Overview or Preview button and select the scan area in the photo. This area is limited only to the area of our table. If we have the option, we can enter the exact value (1507 x 1507 px).
7. We scan the sample by clicking on the Scan button.
5. Preparation of a sample
If the sample has not been previously adapted to work with the EDN program, we must resize the sample to the appropriate size in the digital photo processing program. We assigned to the image a resolution of 300DPI (4).
Of course, there are many programs for digital photo processing, but there are even more commands that can be used to change the mentioned properties of the photograph.
In the link below, are only a few procedures that can be used to resize the image. The procedures show how to work with a ColorBlocker file, but all procedures are the same for working with other files.
6. Coating quality
When we drag a scanned pattern (4) into the Easy Digital Negatives program (5), the program automatically recognizes the sample type.
The EDN displays the coating quality as a graphical (6) representation of each square’s value on the scanned sample.
If the coating of the paper is good, the program marks the coating’s quality with the words Excellent or Good. In poor coating, the application mark the quality of the coating with the inscription Poor (7).
As I mentioned before, this module aims to make the user aware of the quality of his paper coatings.
However, the user’s task is to improve the method of applying the light-sensitive emulsion so that the coating line becomes almost flat (8).
Only on high-quality coated paper will the results of corrections be almost perfect.
A perfectly straight line is, of course, impossible to reach. The quality of the coating is affected by the quality of the paper, and the quality of measuring devices, the quality of the printer, and the like. But we will write more about this below.