Archived from groups: alt.comp.periphs.dcameras (
More info?)
"Ben Hardy" <ben@nemt.me.uk> wrote in message
news:430a515b$0$97133$ed2619ec@ptn-nntp-reader03.plus.net...
> Strewth! Let me get my head round this.
> Obviously, the greater the DPI, the more detail is seen on the print
> Somehow this equates with pixels per inch – the more the better.
> Now you say that: ‘As a general rule, if there is enough pixels to print a
> picture at 300 DPI, then you have made about as good a print that can be
> made.’
> So why is that? Is it due to the limits of the eye or the limits of
> BonusPrint’s printing technology?
It is due to the limits of the paper and the printer and the human eye.
Even with photographic prints made from film, the resolution on paper is
only about 300 dpi. (That has been proven in many tests, and can be found
all over the internet).
Google for "print resolution" without the quotes.
> Whichever, is there any point in allowing for higher DPI?
The higher DPI is needed for larger prints. If you do not have enough
pixels, you get a low resolution print. At some point, the pixels get so
big, you can see the little squares at arms length.
> You comment: ‘since you can only print at one dpi, you have to crop one
> side.’ I don’t understand.
The image dimensions do not fit the dimensions of the paper.
You end up with some part of the image cut off. (That is called cropping).
1728 x 2304 pixel image. The image aspect ratio is 2304/1728=1.33:1 or a 4:3
image.
Paper 6 x 4 inches is 6/4=1.5:1
Paper 10 x 8 inches is 10/8=1.25:1
It is not possible to fit a 4:3 aspect ratio image onto a 1.5:1 or 1.25:1
aspect ratio without cutting off some part of the 4:3 image.
Lets use a 6 x 4 inch paper.
Lets fit one side of the image to the paper.
Lets fit the short side of the paper.
1728 pixels/4 inches=432 ppi.
1728 pixels/432 ppi=4 inches.
2304 pixels/432 ppi =5.33 inches.
Here the image is too short to fill out the 6 inch paper.
Lets fit the long side of the paper.
2304/6 inches=384 ppi.
1728 pixels/384 ppi= 4.5 inches.
2304 pixels/384 ppi= 6.0 inches.
Here the image is too big for the 4 inch dimension, but fits the 6 inch
side.
>
> Many thanks
>
> Ben
>
>
--
CSM1
http://www.carlmcmillan.com
--
>
> CSM1 wrote:
>> "Ben Hardy" <ben@nemt.me.uk> wrote in message
>> news:430a3918$0$97131$ed2619ec@ptn-nntp-reader03.plus.net...
>>
>>>Hi
>>>I'm fairly new to using digicams and I've just one question I'm having
>>>trouble resolving.
>>>Does the amount of megapixels on your camera simply determine the size
>>>of print you can get at the end of the process?
>>>On the Bonusprint website is a chart that shows what size print can be
>>>achieved depending upon the resolution the shot was taken at:
>>>Click on 'Resolution Chart' at here:
>>>http://www.bonusprint.co.uk/pages/digital_prints_quality.htm?OnpageA=1
>>>How does the resolution adjustment on the camera affect the quality of
>>>the picture? Does it simply compress the JPG to a smaller size allowing
>>>for more shots to fit into the given memory at the expense of picture
>>>quality or does it simply reduce the dimensions of the JPG without
>>>compressing it further?
>>>To put it another way, I take a shot at the full resolution my camera is
>>>capable of (1728 x 2304)and then I send the resulting JPG off to the
>>>printer's and have two prints made; one at 10cm x 14cm and one at 20cm x
>>>27cm - in terms of picture quality, which one would be the best, if any?
>>
>>
>> If you printed the 10cm x 14cm using all of the available pixels, then it
>> would have the highest resolution (best print).
>>
>> Digital cameras measure images in pixels, the more pixels you have the
>> better the print can be.
>>
>> As a general rule, if there is enough pixels to print a picture at 300
>> DPI,
>> then you have made about as good a print that can be made.
>>
>> Using a little math.
>> Your image is 1728 x 2304 pixels.
>> for a 300 dpi print you can print at:
>> 1728/300=5.76 inches.
>> 2304/300=7.68 inches.
>> convert inches to cm.
>> 5.76 * 2.54=14.6304 cm
>> 7.68 * 2.54=19.5072 cm
>>
>> Your 10 cm x 14 cm = 3.94 inches x 5.52 inches. Or round to 4 x 6 inches.
>> 1728/4 inches=432 DPI.
>> 2304/6 inches=384 DPI.
>> Since you can only print at one dpi, you have to crop one side. So you
>> get a
>> 384 DPI print for 10 cm x 14 cm.
>>
>> For the 20 cm x 27 cm = 20/2.54=7.87 inches round to 8 inches
>> 27/2.54=10.63
>> inches round to 10 inches.
>> 8 x 10 inch print.
>> 1728/8=216 DPI
>> 2304/10=230 DPI
>> With cropping you get 216 DPI for a 20 cm x 27 cm print.
>>
>> Your smaller print has more resolution.
>>
>> I know it is confusing because you have to convert from cm to inches.
>>
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