DPI

B
Posted By
Bob
Jun 5, 2005
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512
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3
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If I have to make a document in 640×480 in 150 DPI and 1280×1024 in 72 DPI. Is my understanding of DP correct?

640×480 = 8.889" x 6.667" = 59.262963 square inches. 1280×1024 = 17.778" x 14.222" = 252.838716 square inches.

589.262963 x 150DPI = 88389.44445
252.83871 x 72DPI = 18204.387552

The 640×480 has more pixels and should therefore be the "original" that I blow up to 1280×1024?
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E
edjh
Jun 6, 2005
Bob wrote:
If I have to make a document in 640×480 in 150 DPI and 1280×1024 in 72 DPI. Is my understanding of DP correct?

640×480 = 8.889" x 6.667" = 59.262963 square inches. 1280×1024 = 17.778" x 14.222" = 252.838716 square inches.
589.262963 x 150DPI = 88389.44445
252.83871 x 72DPI = 18204.387552

The 640×480 has more pixels and should therefore be the "original" that I blow up to 1280×1024?

Forget about dpi and inches. They are irrelevant until printing time. What counts is the NUMBER OF PIXELS. Are you trying to say that a 640×480 pixel document has more pixels than a 1280×1024 pixel document? Think about it.

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B
bH
Jun 6, 2005
Bob wrote:
If I have to make a document in 640×480 in 150 DPI and 1280×1024 in 72 DPI. Is my understanding of DP correct?

640×480 = 8.889" x 6.667" = 59.262963 square inches. 1280×1024 = 17.778" x 14.222" = 252.838716 square inches.
589.262963 x 150DPI = 88389.44445
252.83871 x 72DPI = 18204.387552

The 640×480 has more pixels and should therefore be the "original" that I blow up to 1280×1024?

640×480 = 307,200 pixels of data
1280×1024 = 1,310,720 pixels of data which is a little more than 4 times the amount of pixels.

If the 640×480 document is printed at 150 DPI, it means that when you print the image 150 pixels in the x resolution will print in 1" and the same for the y resolution. More correctly, 150×150 pixels in a 1" x 1" block, thus 22,500 pixels in 1 square inch … thus the size of the printed image will be 4.26" x 3.2"… (640/150 x 480/150)…

The 1280×1024 document at 72DPI will print at 17.7" x 14.2"(1280/72 x 1024/72)… the recorded image data is greater, the printout is larger, but the print quality will be less since there are less pixels per inch.

bH
T
Tacit
Jun 6, 2005
In article <d802nn$n3e$>, Bob
wrote:

640×480 = 8.889" x 6.667" = 59.262963 square inches.

No, 640×480 is 640 pixels by 480 pixels. The number of "inches" depends on the resolution. 640×480 at 640 pixels per inch is 1 inch wide. 640×480 at 320 pixels per inch is 2 inches wide. And so on.

640×480 has FEWER pixels than 1280×1024. 640×480 means 640 pixels wide and 480 pixels high. 1280×1024 means 1,280 pixels wide and 1,024 pixels high.

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