How many megapixels for at 8x10 with 300dpi?

Started Jul 15, 2003 | Discussions
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momof3b1g Regular Member • Posts: 125
How many megapixels for at 8x10 with 300dpi?

How many mp would i need if i wanted an 8x10 with 300 dpi?

Can someone give me the formulation to figure this out. The norm is usually 3mp for up to 11x14. But 300dpi is the recommended dpi. So a 3mp would only give you a 5x7.

Steve Cavigliano Veteran Member • Posts: 6,369
Re: How many megapixels for at 8x10 with 300dpi?

Mom,

This was just posted the other day. I believe the number was a little over 7mpxl's.

FWIW, IMHO, if you are printing at home, you won't see much, if any difference, between 300dpi, and say 180-200dpi, on a 8X10. So you can "up-size" (interpolate) to get your 300dpi, or you can leave the images alone and print with what you have. A 3mpxl image will normally make a very decent 8X10. If you need to print larger, a 5 mpxl image will work well, up to, double that size (16X20).

If you are specifically needing "publication ready images" of 300dpi, then ignore the above information and look into re-sizing software like Genuine Fractals.

Steve

momof3b1g wrote:

How many mp would i need if i wanted an 8x10 with 300 dpi?
Can someone give me the formulation to figure this out. The norm is
usually 3mp for up to 11x14. But 300dpi is the recommended dpi. So
a 3mp would only give you a 5x7.

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SeanU Senior Member • Posts: 2,070
Re: How many megapixels for at 8x10 with 300dpi?

8*300 = 2400
10*300 = 3000

3000 * 2400 = 7.2mp

One solution is to upsize the image in Photoshop etc. so it matches the desired DPI. The other solution is to use a lower DPI setting. Stair interpolation does very well when upsizing (do a search).

Sean

momof3b1g wrote:

How many mp would i need if i wanted an 8x10 with 300 dpi?
Can someone give me the formulation to figure this out. The norm is
usually 3mp for up to 11x14. But 300dpi is the recommended dpi. So
a 3mp would only give you a 5x7.

Caer Senior Member • Posts: 2,160
Re: How many megapixels for at 8x10 with 300dpi?

momof3b1g wrote:

How many mp would i need if i wanted an 8x10 with 300 dpi?
Can someone give me the formulation to figure this out. The norm is
usually 3mp for up to 11x14. But 300dpi is the recommended dpi. So
a 3mp would only give you a 5x7.

You'd need a 3000×2400 image, which is 7.2MP.

The calculation is quite simple. DPI means dots per INCH. You want a print 10 INCHes wide, so for 300 dots per inch you need 300×10 dots, or 3000.

brianj Forum Pro • Posts: 14,657
Re: How many megapixels for at 8x10 with 300dpi?

300dpi is only an arbitary figure anyway. Why not go for 400 or 500dpi.

Brian

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John Burns Veteran Member • Posts: 3,634
Re: How many megapixels for at 8x10 with 300dpi?

Caer wrote:

You'd need a 3000×2400 image, which is 7.2MP.

The calculation is quite simple. DPI means dots per INCH. You want
a print 10 INCHes wide, so for 300 dots per inch you need 300×10
dots, or 3000.

True enough but you're not multiplying dots but pixels. What you are talking about here is pixels per inch(ppi) not dots per inch(dpi). dpi is a printer term used to describe how many ink dots a printer can lay down in an inch. It can, and usually does, require several dots to reproduce a pixel.

-- hide signature --

John

Ron Parr Forum Pro • Posts: 13,775
Re: How many megapixels for at 8x10 with 300dpi?

brianj wrote:

300dpi is only an arbitary figure anyway. Why not go for 400 or
500dpi.

It's hard to notice improvements beyond 300 dpi under normal viewing conditions.

Chris R-UK Forum Pro • Posts: 16,076
Re: How many megapixels for at 8x10 with 300dpi?

Ron Parr wrote:

brianj wrote:

300dpi is only an arbitary figure anyway. Why not go for 400 or
500dpi.

It's hard to notice improvements beyond 300 dpi under normal
viewing conditions.

-- hide signature --

Ron Parr

Just to point out that, when printing a photo at best quality, the printer driver will interpolate up to 600 PPI for a Canon, 720 PPI for an Epson and 600-1200 PPI for an HP. Nothing to do with photo quality, these are just the standard resolutions that the printer requires to generate its pattern of dots.
--
Chris R

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Ernest Nitka Junior Member • Posts: 33
Re: How many megapixels for at 8x10 with 300dpi?

momof3b1g wrote:

How many mp would i need if i wanted an 8x10 with 300 dpi?
Can someone give me the formulation to figure this out. The norm is
usually 3mp for up to 11x14. But 300dpi is the recommended dpi. So
a 3mp would only give you a 5x7.

Am I missing somethiing here? 300 dpi for an 8 x 10 = 20 MB image size ( 8 x 300 = 2400, 10 x 300 = 3000. 2400 x 3000 = 7.2 Meg but for RGB you must take 7.2 x 3 = 20 0r 21 MB )

To figure our if your digicam will do the trick you need to find out the MB output of the camera - my D100 makes a TIFF of about 17 MB at highest resolution so 8 x 10 at slightly less than 300 dpi is possible.

Is my math wrong?

ernie nitka

Ron Parr Forum Pro • Posts: 13,775
Re: How many megapixels for at 8x10 with 300dpi?

Ernest Nitka wrote:

Am I missing somethiing here? 300 dpi for an 8 x 10 = 20 MB
image size ( 8 x 300 = 2400, 10 x 300 = 3000. 2400 x 3000 = 7.2
Meg but for RGB you must take 7.2 x 3 =
20 0r 21 MB )

To figure our if your digicam will do the trick you need to find
out the MB output of the camera - my D100 makes a TIFF of about 17
MB at highest resolution so 8 x 10 at slightly less than 300 dpi is
possible.

Is my math wrong?

Convoluted, but not wrong.

If you scale a 3000x2000 image so that the longest dimension is 10 inches, then the narrow dimension must be less than 8 inches. Thus, if you don't crop, you can print a 3000x2000 image at 300 dpi, 10x6.67. If you want a 10x8 image, then you need to crop out a portion of your 3:2 image with a 5:4 aspect ratio and print this. You won't be able to reach 300 dpi after you've cropped and printed at 10x8.

Chris R-UK Forum Pro • Posts: 16,076
Re: How many megapixels for at 8x10 with 300dpi?

Ernest Nitka wrote:

momof3b1g wrote:

How many mp would i need if i wanted an 8x10 with 300 dpi?
Can someone give me the formulation to figure this out. The norm is
usually 3mp for up to 11x14. But 300dpi is the recommended dpi. So
a 3mp would only give you a 5x7.

Am I missing somethiing here? 300 dpi for an 8 x 10 = 20 MB
image size ( 8 x 300 = 2400, 10 x 300 = 3000. 2400 x 3000 = 7.2
Meg but for RGB you must take 7.2 x 3 =
20 0r 21 MB )

To figure our if your digicam will do the trick you need to find
out the MB output of the camera - my D100 makes a TIFF of about 17
MB at highest resolution so 8 x 10 at slightly less than 300 dpi is
possible.

Is my math wrong?

ernie nitka

Your answer in correct, but you are talking about file sizes in MB whereas everybody else is talking about image sizes in pixels (in spite of using dpi, they really mean ppi). Clearly a 7.2 MP image would produce a 21.6 MB file if saved as a TIFF.
--
Chris R

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Qwerty13 Contributing Member • Posts: 522
Re: How many megapixels for at 8x10 with 300dpi?

This is just a math question.

8x300=2400, 10x300=3000. So you need a camera that shoots 2400x3000 pixels or 7.2 megapixel.

This is regardless of whether or not you "need" 300 dots in every inch. You have determined your need and math has answered your question. All praise the all mighty math god!

momof3b1g wrote:

How many mp would i need if i wanted an 8x10 with 300 dpi?
Can someone give me the formulation to figure this out. The norm is
usually 3mp for up to 11x14. But 300dpi is the recommended dpi. So
a 3mp would only give you a 5x7.

David AA Forum Member • Posts: 75
Re: How many megapixels for at 8x10 with 300dpi?

Isn't it true to say that the definition of a megapixel is (1024X1024) pixels not 1,000,000 pixels.

Therefore, strictly speaking you need (2400x3000) 1,048,576= 6.87megapixels.

It all depends I suppose on how your camera manufacturer defines its megapixels ;o).

David AA

Qwerty13 wrote:
This is just a math question.

8x300=2400, 10x300=3000. So you need a camera that shoots 2400x3000
pixels or 7.2 megapixel.

This is regardless of whether or not you "need" 300 dots in every
inch. You have determined your need and math has answered your
question. All praise the all mighty math god!

momof3b1g wrote:

How many mp would i need if i wanted an 8x10 with 300 dpi?
Can someone give me the formulation to figure this out. The norm is
usually 3mp for up to 11x14. But 300dpi is the recommended dpi. So
a 3mp would only give you a 5x7.

tyoung Veteran Member • Posts: 8,375
Re: How many megapixels for at 8x10 with 300dpi?

momof3b1g wrote:

How many mp would i need if i wanted an 8x10 with 300 dpi?
Can someone give me the formulation to figure this out. The norm is
usually 3mp for up to 11x14. But 300dpi is the recommended dpi. So
a 3mp would only give you a 5x7.

Heee heee, You've got an awful lot of answers here, and they are all basically correct, but reflect various different approaches to the same problem. You're also correct in your own assumptions above. You could get an 11 x 14 image with your 3mp camera, but you'd have to add pixels by some kind of interpolation in order to get a print that size. In effect, making an enlargement. Success in an enlargement like this would depend on the interpolation method chosen, the image itself and how it would be viewed. Similarly to the requirements of pulling a good 11 X 14 print from a 35mm negative. A 7.2Mp camera could do the job with no or very little interpolation/enlargement. 5Mp's could also get the job done, but with some relatively mild interpolation.

Going one to one with no interpolation would generally give you the best result, or at least the most faithful rendition of the original, but if an enlargement is required, careful interpolation can often yield an enlargement of very good quality.
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http://www.pbase.com/tyoung/

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Just Looking Veteran Member • Posts: 5,740
Re: How many megapixels for at 8x10 with 300dpi?

David,

If you manufactured a camera with 7,200,000 pixels, would you market it as 6.87 MP? I didn't think so, and neither would anyone else.

In fact, cameras with 1280x960, or 1,228,000 pixels, are marketed as 1.3 MP. That is, the standard is to exaggerate.

Calling a one-color pixel sensor (that measures one-third of the information in a color pixel) a "pixel" is a three-times exaggeration to start with, so why stop there?

j

David AA wrote:
Isn't it true to say that the definition of a megapixel is
(1024X1024) pixels not 1,000,000 pixels.

Therefore, strictly speaking you need (2400x3000) 1,048,576=
6.87megapixels.

It all depends I suppose on how your camera manufacturer defines
its megapixels ;o).

David AA

Qwerty13 wrote:
This is just a math question.

8x300=2400, 10x300=3000. So you need a camera that shoots 2400x3000
pixels or 7.2 megapixel.

This is regardless of whether or not you "need" 300 dots in every
inch. You have determined your need and math has answered your
question. All praise the all mighty math god!

momof3b1g wrote:

How many mp would i need if i wanted an 8x10 with 300 dpi?
Can someone give me the formulation to figure this out. The norm is
usually 3mp for up to 11x14. But 300dpi is the recommended dpi. So
a 3mp would only give you a 5x7.

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