★ HARDWARE Manual ★ VDP2 User's Manual ★ Chapter 12 Color Calculation
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VDP2 User's Manual / Chapter 12 Color Calculation

● Extended color calculation function

The extended color calculation function is a function that converts the result of adding the second image and the third image at a fixed ratio into the data of the second image. By performing color calculation on this second image and top image, it is possible to perform color calculation on three screens. When a line color screen is inserted, the result of color calculation of the third image and the force image at a fixed ratio is used as the data of the third image, and the third image and the line color screen are displayed.

Since the result of adding at a certain ratio is used as the data of the second image, color calculation on 4 screens can be performed. However, the extended color calculation function can be used only when the TV screen mode is normal mode, not when it is in high resolution or dedicated monitor mode.
When performing the extended color calculation, whether to add the third image and the force image depends on the color calculation enable bit of the screen of the third image, and whether to add the second image and the third image is the color calculation of the screen of the second image. Follows the enable bit.
The extended color calculation ratio when using the extended color calculation function varies depending on the color RAM mode, line color screen insertion, color calculation enable bit value and color format of the second and third images, and the color format of the force image.
The extended color calculation function is shown in Figure 12.3, and the extended color calculation ratio is shown in Table 12.2.

Figure 12.3 Extended color calculation function
● Normal case ・ When the color calculation enable bit of the second image is 0　
┌──────┐ ┌──────┐
│ │ │ Extended color │
│ Second image │ → │ After calculation │ │
│ │ │ Second image │
└──────┘ └──────┘
　
-When the color calculation enable bit of the second image is 1.　
┌──────┐ ┌──────┐ ┌──────┐
│ │ │ │ │ Extended color │
│ Third image │ ＋ │ Second image │ → │ After calculation │ │
│ │ │ │ │ │ Second image │
└──────┘ └──────┘ └──────┘
　
● When a line color is inserted　
-When the color calculation enable bit on the line color screen is 1.　
-When the color calculation enable bit of the third image is 0　
┌──────┐ ┌──────┐ ┌──────┐
│ │ │ Line color │ │ Extended color │
│ Third image │ ＋ │ │ → │ After calculation │
│ │ │ screen │ │ second image │
└──────┘ └──────┘ └──────┘
　
-When the color calculation enable bit on the line color screen is 1.　
-When the color calculation enable bit of the third image is 1.　
┌──────┐ ┌──────┐ ┌──────┐ ┌──────┐
│ │ │ │ │ │ │ │ Extended color │
│ Force image │ ＋ │ Third image │ ＋ │ Second image │ → │ After calculation │
│ │ │ │ │ │ │ │ Second image │
└──────┘ └──────┘ └──────┘ └──────┘

Table 12.2 Extended color calculation ratio
 Color
 RAM
 mode
 Line color screen
 Color format
 Color operation enable bit value
 Extended color calculation ratio Second: Third: Force image image image image
 Second picture
 Third
 image
 Force image
 Second picture
 Third
 image
 Mode 0
 Do not insert Palette or
RGB format		 Palette or
RGB format		 − 0 − 4: 0: 0
1 − 2: 2: 0
insert − Palette or
RGB format		 Palette or
RGB format		 0 0 or 1 4: 0: 0
1 0 2: 2: 0
1 1 2: 1: 1
 Mode 1
 Or mode 2
 Do not insert Palette or
RGB format		 Palette format − 0 or 1 − 4: 0: 0
RGB format − 0 − 4: 0: 0
1 − 2: 2: 0
insert − Palette format Palette or
RGB format		 0 or 1 0 or 1 4: 0: 0
RGB format Palette format 0 0 or 1 4: 0: 0
1 0 or 1 2: 2: 0
RGB format 0 0 or 1 4: 0: 0
1 0 2: 2: 0
1 1 2: 1: 1
[note]
When the TV screen mode is high resolution or dedicated monitor mode, the extended color calculation function cannot be used.
When inserting a line color screen, the color format of the second image will be the palette format.
The extended color calculation ratio is for the value obtained by multiplying each RGB data by 1/4.

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★ HARDWARE Manual ★ VDP2 User's Manual ★ Chapter 12 Color Calculation
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