JPH04145772A - Deciding method for image quality in transfer photographic printing method - Google Patents

Abstract

PURPOSE:To obtain the objective decision by a quantitative measurement by deciding the image quality by an inclination of a straight line approximating a correlation of each boundary value and a logarithm of a void area. CONSTITUTION:With regard to a measuring object area, color density level data of each unit picture element of a transfer image generated on an image receiving sheet by supplying photographic printing energy of prescribed density is compared with each boundary value set by plural color density levels selected within a range of a color density level, and an area of the part of color density being under the boundary value is calculated as a void area at every boundary value. Subsequently, a correlation of both for setting each boundary value and a logarithm of each corresponding void area as an X axis value and a Y axis value, respectively is approximated by a straight line, and by an inclination of the straight line, the image quality is decided. In such a way, the image quality is measured quantitatively by numerical value, and can objectively be decided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for quantitatively determining image quality in a transfer printing method.

[Prior Art] In the transfer printing method, a transfer sheet having a colorant layer and an image-receiving sheet are placed on top of each other, and a transferred image is printed on the image-receiving sheet by supplying printing energy (for example, thermal energy) to the back side of the transfer sheet. It's something you get.

Conventionally, the method of determining the image quality of transferred images obtained by transfer printing methods, that is, transferred prints, is to visually observe abnormal transfer conditions such as density unevenness and missing or missing dots forming the image. , a method for determining image quality is used.

Image quality depends on the materials used in the transfer printing method, such as transfer sheets (for example, ink transfer sheets) and image-receiving sheets (for example, photographic paper or image-receiving paper), and the control of printing energy supply means for transfer, such as thermal heads and laser beams. Quantitatively measuring the image quality of transferred prints and determining trends is important in confirming the direction of material development and improving the hardware configuration. It has become an important indicator.

[Problems to be Solved by the Invention] However, in the conventional method of visually determining the image quality of a transferred print, the environment in which the sample to be determined is visually observed (
The criteria for judging image quality can vary greatly depending on factors such as temperature, humidity, light source conditions, etc.), the physical condition of the visual judge, the image of the sample to be judged at the time, and the condition of the previously viewed sample. For samples to be determined that have only a slight difference in image quality, the determination may vary each time the determination is made.

Furthermore, the judgments made will change even if different judges perform visual inspections, and in the end only samples with large differences will be able to obtain reliable judgments. It was impossible to judge the image quality of transferred prints.

As a result of extensive research, the inventors of the present invention have focused on the fact that unevenness in density that occurs in transferred prints, chipped or missing dots that form images, etc. degrade image quality. The present invention was completed based on the idea that quantification and judgment can be made by measuring the degree of chipping, omission, etc. of dots forming an image and converting it into numerical values.

That is, an object of the present invention is to provide a method for quantitatively measuring and objectively determining the image quality of a transferred print.

[Means for Solving the Problems] Therefore, the gist of the present invention is to superimpose a transfer sheet having a colorant layer and an image-receiving sheet, and supply printing energy to the back side of the transfer sheet. In a transfer printing method that involves obtaining a transferred image, in order to judge the image quality of the transferred image, at least the area to be measured is determined by: (b) Processing the obtained transferred image with an image processing device to obtain color density level data for each unit pixel of the processing; (e) Selecting within the range of the color density level. (d) Compare the color density level data of all unit pixels with each set boundary value, and set the color density level less than the boundary value for each boundary value. (e) Each boundary value is the X-axis value, and each corresponding white area is the logarithm of the area.The correlation between the two is approximated by a straight line, and A method for determining image quality in a transfer printing method includes the following steps: determining the image quality based on the slope of a straight line.

The present invention will be explained in detail below.

First, the basic idea on which the present invention is based will be explained.

As mentioned above, image quality can be judged by measuring the degree of uneven density of the image, missing dots forming the image, etc. , omissions, etc. are considered to be due to the fact that the color is not in the desired density where it should be, and [the white area where the normal color density is not colored] degrades the image quality of the transferred print. It is thought that

Therefore, by measuring this [white portion], it is possible to quantitatively express the image quality of the transferred print.

The method for calculating the area of the white part J, which is not colored with the normal color density, of the sample to be determined is basically the following (a).
It includes three steps of ~(C).

(a) A transferred image is obtained on an image-receiving sheet by supplying printing energy at a constant density to the back side of the transfer sheet.

(b) Processing the transferred image with an image processing device to obtain color density level data for each unit pixel of the processing.

(C) Compare each of the above data with a certain color density level,
The area of the portion with the color density below the level is calculated as the area of the white area.

Although the specific procedure is not particularly limited, for example, it is as follows.

■ Keep the temperature environment constant and stable during sample preparation of printing machines, image receiving paper, etc., keep the pressure constant, and keep the printing start temperature constant and the printing temperature constant (preventing energy increase due to heat accumulation) ) to create a sample of the transfer print.

In particular, printing in a single color of magenta is effective when capturing images with a camera and in correspondence with visual inspection, but even with other colors or transfer prints with full-color images, it is difficult to print inside the measurement target area. If no energy density gradient occurs, it is valid as a sample.

The area to be measured is only a certain area of a certain place on the sample.
That is, it is extracted as a determination location and captured as an image into image processing equipment.

The captured image is recognized by unit pixels of appropriate size, and color density level data for each unit pixel is obtained.

■ Each data is binarized at a certain color density level and the image is displayed in two colors. At this time, it is best to process the image as a negative image so that the areas with color density below the level remain black.

The area of the white part (black part if negative processing is performed) after image processing, that is, the area of the white part, is measured.

■ ■ ■ The ratio of the area of the white area to the area of the determination area (hereinafter referred to as the area ratio J of the white area) itself is data that reflects the image quality. In particular, whiteness obtained by binarizing at the color density level that should originally be obtained (hereinafter referred to as "regular level") using a fixed density of printing energy supplied to the back of the transfer sheet when creating a transfer print sample. The cutout area ratio reflects the image quality fairly well, and can also be used to judge the image quality.

Although the normal level mentioned above, that is, the normal color density level, can be easily determined, for example, from a complete ideal color density sample or from color density level distribution data, , "regular level"
takes on distinct values, so a step is required to determine the normal level for each individual sample. Therefore, for any sample to be determined, it is preferable to make absolute measurements so that the measured values can be directly compared without worrying about the "normal level" and the superiority or inferiority of performance can be determined. However, in the present invention, the following ( This is accomplished by steps (d).

(C') Binarize the color density level data using multiple boundary values, and calculate the area of the white area for each boundary value. (d) Each boundary value is the X-axis value, and each corresponding white area is the area. The correlation between the two is approximated by a straight line using the logarithm of the Y-axis value, and the slope of this straight line is determined. If the value is large, the image quality is determined to be high, and if the value is small, the image quality is determined to be low.

Although the specific procedure for determining the slope of the above-mentioned correlation line is not particularly limited, it is, for example, as follows.

■ Sequentially perform binarization at each boundary value from light density (white side) to normal color density (for example, each step in which the color density from white to black is divided into θ to 256 tones). In addition, the area of the white outline is measured.

■ The relationship between the color density level and area for white areas, which were determined in the work in ■ above, is expressed using the normal color density as the origin, color density is expressed on the X axis, and area for white areas is expressed on the logarithmic axis on the Y axis. do.

(2) The obtained data is approximated by a straight line, and the image quality is determined based on the gradient of this straight line. The numerical value of the slope of the straight line can be used as a qualitative expression of image quality (for example, "Excellent", "Good", "Acceptable", "
If it is necessary to correspond to "impossible", etc., it can be determined empirically from data on the correspondence between the numerical value of the slope of the straight line and the visual judgment.

[Examples] Next, specific embodiments of the present invention will be explained in more detail using Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

The samples were prepared using a dye sublimation type transfer sheet and using various types of sublimation dye receiving type photographic paper (image receiving paper).

The sample was created by applying a constant density of printing energy, keeping the pressure constant, keeping the printing start temperature constant, and controlling the printing energy after printing started, taking into account the heat storage effect of the thermal head. The transfer sheet was created by controlling the application of a constant amount of thermal energy to the back surface of the transfer sheet.

The following image receiving sheet was used.

No. 1 Photographic paper based on synthetic paper No. 2 Photographic paper based on paper (cellulose) with medium thickness of the dyed layer No. 3 Photographic paper based on paper (cellulose) Paper with a thick dyeing layer No. 4 Photographic paper based on paper (cellulose) with a thin dyeing layer No. 5 PET (polyethylene terephthalate) foam
Photographic paper No. 6 based on opalescent PET The above-mentioned image receiving sheets were used, magenta was used as the transfer sheet, and printing energy of 0.21 W/dot was supplied. A sample of the transferred print was created.

A 4 mm x 15 mm area on the transferred image of each sample was used as the judgment location, and together with a common standard color sample, a particulate image analysis system was used as an image processing program with image processing equipment (manufactured by Mitsubishi Kasei, trade name: MKSIPS). ), images were captured at a resolution of 1600 pixels per 1 mm2.

To determine whether the image has been captured correctly, use the color density level of the standard color sample as a reference, and check whether the color density of the standard color sample always shows the same level and ensure that each sample is captured consistently and stably. I checked to see if it was correct.

If the image is normal, the area to be measured on the CRT of the image processing equipment has a color density level (
For example, in negative processing, binarization was sequentially performed for each boundary value in the range from the color density level at which a black dot begins to appear at the determination location to the normal color density level, and the area of white areas was measured.

Based on the above data, for each sample, the color density level is the X-axis value, and for white areas, the logarithm of the area is the Y-axis value.The correlation between the two is approximated by a straight line using the method of least squares, and the slope of each straight line is calculated. Ta.

The results are shown in Table 1 in comparison with the visual judgment results according to the conventional method.

As mentioned above, the determination results based on the slope values obtained by the method of the present invention were in good agreement with the visual determination results.

rEffect of invention] The method of the present invention achieved the following effects.

(1) The image quality of transferred prints, which was previously judged visually, can now be expressed quantitatively using numerical values.

(2) Judgments are no longer influenced by the person making the judgment, the date and time, or the viewing environment.

(3) Subtle differences can now be judged objectively without being influenced by images.

(4) Accumulation of data and therefore analysis became possible.

Claims (1)

[Claims] (1) In the transfer printing method, which involves overlapping a transfer sheet having a colorant layer and an image-receiving sheet and supplying printing energy to the back side of the transfer sheet, a transferred image is obtained on the image-receiving sheet. In determining the image quality, at least for the area to be measured, (a) obtaining a transferred image on an image receiving sheet by supplying printing energy at a constant density to the back side of the transfer sheet; (b) using the obtained transferred image; (c) setting a plurality of color density levels selected within the range of the color density level as a boundary value; d) Comparing the color density level data of all unit pixels with each set boundary value, and calculating the area of the part whose color density is less than the boundary value for each boundary value as the white area, and (e ) approximating the correlation between the two by a straight line, where each boundary value is the X-axis value and the logarithm of each corresponding white area is the Y-axis value, and the image quality is determined based on the slope of the straight line. A method for determining image quality in a transfer printing method, characterized by: