Image Pixel and Photo Print


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arthur_koh

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#1
For those who are interested in sending their digital image for photo print,

I got below info from
http://www.kodakexpress.com.sg
and
http://www.megapixel.net/html/issueindex.html

PRINT SIZE------- 3R(3"x5")-- 4R(4"x6")---5R(5"x7")
MIN. RES (pixels) 640x480--- 1024x768--1280x1024

PRINT SIZE------- 6R(6"x8")----8R (8"x10")--- S8R (8"x12")
MIN. RES (pixels) 1600x1200--1800x1200---1800x1200

PRINT SIZE------- 10R (10"x12")---S10R (10"x15")
MIN. RES (pixels) 1800x1200------1800x1200

(the --- lines are there to help me ctrl the spacing)

If I perform the calculation:
640 x 480 = 307 200 pixel
1024 x 768 = 786 432 pixel
1280 x 1024 = 1 310 720 pixel = 1.3 megapixel
1600 x 1200 = 1 920 000 pixel = 2.1 megapixel
1800 x 1200 = 2.3 megapixel
2048 x 1536 = 3 megapixel
2400 x 1600 = 4 megapixel

If I am sending my photo for 4R print, my image size has to be at least 1024 x 768 pixels. A 1.3 megapixel Digicam is sufficient. From the calculation above, a 2.3 megapixel camera will allow me to print a 10" by 15" photo at any Kodak outlet.

So, what’s the use of a higher megapixel camera?
It will capture image at higher pixel size and give more details but it will take up more memory space. For eg: If I capture an image at 2048 x 1536 and another at 640 x 480. Then extract a 640 x 480 from 2048 x 1536 image and compare it to the one taken at 640 x 480, I would see more details but the extracted image would be a cropped one. To see more information and pictures about this, you can go to:
http://www.megapixel.net/html/issueindex.html
(Go to->Articles ->Common types of resolutions)
According to the information from the above web site:

“Generally, most digital cameras have little problems yielding a sharp and well-defined image with subjects 1 to 5 meters away (3 to 15 feet).

Distant landscapes, which by their very nature, tend to contain a large amount of small detail, will generally turn out "sharper" and clearer with cameras that use 2 megapixel, and above, CCDs.

1.3 and 1.5 million pixel cameras, will produce acceptably detailed images with subjects 30 metres (90 to 100 feet) away. After that, their photos tend to become a bit more impressionistic.

The rule of thumb is simple: the greater the complexity of the subject, the greater the number of pixels required”

Hope the above info is helpful to you.
Regards, Arthur
 

erwinx

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Jan 18, 2002
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#2
A simple rule of thumb (one discussed here often)

300 dpi is best

so 'best' for 4R will be 1600x1200
 

hazardman

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I need to enlarge a print...but i did some touching up in PS for my friend. Thus i scanned at Photoelite@adelphi centre $13.90, ultra high res. Then they tell me max they can print is only 10 x 15. I am actually printing 16 x 20. Abit of a dilemma here...
 

#5
This isn't exactly related, but say you want to send your images to your own inkjet photo printer, here's what I learnt about printing 4R, 5R, 8R prints on your injets.
As extracted from the DPreview.com forum

<<<
Most of us will agree that resolving an image at 200 pixels per inch (ppi) is about as low as you can go and still maintain 'good'-quality normal-sized prints, and that using greater than 360 generally won't produce better looking prints than 300.

The printer's dots per inch (dpi) is the rate at which it can lay ink on the paper. You should resolve the IMAGE recognizing the printer's base resolution. The Epsons use 720dpi, the Canons
600.

Resolve your image using a ppi rate that is a whole-number lower multiple of your printers' base resolution. For Epsons, the ideal pic resolution is 360, with 240 being a good choice for
less-critical work. With a Canon, 300 is about as good as it gets (altho I SUPPOSE sending one at 600ppi wouldn't hurt, but the pic will have to be fairly small or the file will be HUGE). Use
200ppi for less-critical work.

Using resolutions other than whole divisors of the base resolution requires the printer's processor to reinterpolate the pic, and I and lots others believe that Photoshop or Genuine
Fractals or whatever editor you use is lots more skillful at interpolation than the printer.

So reinterpolate your pics to one to 2 resolutions depending on your printer's base resolution and you and your printer will be happy.
>>>

About Printer Colour
<<<
300 dots per inch is enough if every one of those dots can be made exactly the correct color from the possible 16 million colors available in the digital photo. CRT screens can do this, and also
dye sublimation type printers.

However, this is not the case with inkjet printers since they do not have 16 million different inks, rather, thay have only 4 or 6 or 7 inks and they have to print multiple dots in a 2x2 or 3x3
superdot in order to average out the color in that superdot and make it look like one of the 16 million.

That is why you must take the inkjet dpi & divide by 2 or 3 to understand what the printer is capable of when asked to print true color.
>>>

So say for
4R - 4"x6", for a base DPI of 300, we need 1200x1800 image or 2,160,000 pixels
5R - 5"x7", for a base DPI of 300, we need 1500x2100 image or 3,150,000 pixels
8R - 8"x10", for a base DPI of 300, we need 2400x3000 image or 7,200,000 pixels

It's good to adjust the image first to the corresponding dimensions before printing, for better quality & speed. Extrapolation (if your pixels is not enough) done by fractals
will create a more natural look. I'm presuming software like Qimage will also do some intelligent extrapolation
before sending it to the printer, if not photoshop should do it.

This is just some sharing of technical information for your reference. It has helped me clear some doubts about printing.

Colour management, now that's another challenge!!! ;p

Hope this helps.

-ptl-
 

hazardman

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#6
btw, they say tif n jpeg when printing got no diff. Issit true?? I always use tif to print when i do my design work.... thus when i gave em tif they say they gonna charge me $1 for conversion to jpeg. :(
 

shawntim

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Feb 13, 2002
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#7
Originally posted by erwinx
A simple rule of thumb (one discussed here often)

300 dpi is best

so 'best' for 4R will be 1600x1200
the maths abit sar lah.. should be 1800 x 1200
 

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