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-   -   Resolution, dpi, & pixelation for printing. (http://www.velocityreviews.com/forums/t430578-resolution-dpi-and-pixelation-for-printing.html)

Ben Bowen 11-16-2006 04:56 PM

Resolution, dpi, & pixelation for printing.
 
Hi all. I just sent out a bunch of pictures to get processed. They were
taken with my new Canon A640 (10MP). I re-sampled the pix using Corel
Photopaint to 1024 x 768 to print 4" x 6" prints, because 10MP are too
big to upload. I believe that is the correct resolution to use,
however, a lot of the pictures are pixelated. So now, I'm trying to
debug what I did wrong. I previously had a Canon Powershot S300 (2MP)
and never had these problems. I camera takes pix at 72dpi and the
re-sampled pix have 72dpi too, so I doubt it could be that. Did I
decrease the resolution too much? Should I make it 1200x1600? When I
print the images at home (from orignial not-resampled images) I have no
problem, but the re-sampled images I uploaded are no good. I will try
various combos of re-sampling to experiment, but I'd like to have an
idea of what I'm shooting for.

Thanks...


bugbear 11-16-2006 05:22 PM

Re: Resolution, dpi, & pixelation for printing.
 
Ben Bowen wrote:
> Hi all. I just sent out a bunch of pictures to get processed. They were
> taken with my new Canon A640 (10MP). I re-sampled the pix using Corel
> Photopaint to 1024 x 768 to print 4" x 6" prints, because 10MP are too
> big to upload. I believe that is the correct resolution to use,
> however, a lot of the pictures are pixelated. So now, I'm trying to
> debug what I did wrong. I previously had a Canon Powershot S300 (2MP)
> and never had these problems. I camera takes pix at 72dpi and the
> re-sampled pix have 72dpi too, so I doubt it could be that. Did I
> decrease the resolution too much? Should I make it 1200x1600? When I
> print the images at home (from orignial not-resampled images) I have no
> problem, but the re-sampled images I uploaded are no good. I will try
> various combos of re-sampling to experiment, but I'd like to have an
> idea of what I'm shooting for.


Your S300 was generating (as max) 1600x1200, so I'd aim
for that.

BugBear

Ken Weitzel 11-16-2006 05:26 PM

Re: Resolution, dpi, & pixelation for printing.
 
Ben Bowen wrote:
> Hi all. I just sent out a bunch of pictures to get processed. They were
> taken with my new Canon A640 (10MP). I re-sampled the pix using Corel
> Photopaint to 1024 x 768 to print 4" x 6" prints, because 10MP are too
> big to upload. I believe that is the correct resolution to use,
> however, a lot of the pictures are pixelated. So now, I'm trying to
> debug what I did wrong. I previously had a Canon Powershot S300 (2MP)
> and never had these problems. I camera takes pix at 72dpi and the
> re-sampled pix have 72dpi too, so I doubt it could be that. Did I
> decrease the resolution too much? Should I make it 1200x1600? When I
> print the images at home (from orignial not-resampled images) I have no
> problem, but the re-sampled images I uploaded are no good. I will try
> various combos of re-sampling to experiment, but I'd like to have an
> idea of what I'm shooting for.


Hi Ben...

1024 isn't sufficient to produce good 6x4's. If you must resize,
then shoot for at least 200 and preferably 300 - meaning that
6 inches x 200 = a minimum of 1200, and 6 inches x 300 = the
more preferable 1800.

If you're resizing only because 10 megs is too big, you might
try leaving the size alone, and reducing file size by slightly
increasing the jpeg compression. I suspect you'd like this
better.

Fortunately prints are cheap, do yourself some experimenting :)

Finally, forget that 72 dpi thing. For what you're doing now,
it's meaningless.


Take care.

Ken




Digital Photography Now 11-16-2006 05:29 PM

Re: Resolution, dpi, & pixelation for printing.
 
200 image pixels per printed inch is a reasonable target to aim for, though
300ppi would be ideal. 1024x768 is under 200ppi, so you could get some
pixellation. If you are worried about upload sizes, resize to 1600x1200. But
I would also consider trying a different online service as most decent ones
will accept full size images now and others will compress your full size
images as part of the upload process.

Ian

Digital Photography Now
http://dpnow.com

"Ben Bowen" <bozothedeathmachine@gmail.com> wrote in message
news:1163696164.044839.258640@b28g2000cwb.googlegr oups.com...
> Hi all. I just sent out a bunch of pictures to get processed. They were
> taken with my new Canon A640 (10MP). I re-sampled the pix using Corel
> Photopaint to 1024 x 768 to print 4" x 6" prints, because 10MP are too
> big to upload. I believe that is the correct resolution to use,
> however, a lot of the pictures are pixelated. So now, I'm trying to
> debug what I did wrong. I previously had a Canon Powershot S300 (2MP)
> and never had these problems. I camera takes pix at 72dpi and the
> re-sampled pix have 72dpi too, so I doubt it could be that. Did I
> decrease the resolution too much? Should I make it 1200x1600? When I
> print the images at home (from orignial not-resampled images) I have no
> problem, but the re-sampled images I uploaded are no good. I will try
> various combos of re-sampling to experiment, but I'd like to have an
> idea of what I'm shooting for.
>
> Thanks...
>




www.thephotoboard.com 11-16-2006 05:51 PM

Re: Resolution, dpi, & pixelation for printing.
 
hi ben, try downloading yor pics from the cam at 300dpi, and then
resize to 1800 x 1200px, that would give you an imagesize of 4x6, i
found a great utility for this type of calculation

http://auctionrepair.com/pixels.html


i hoped this helps


Ben Bowen wrote:
> Hi all. I just sent out a bunch of pictures to get processed. They were
> taken with my new Canon A640 (10MP). I re-sampled the pix using Corel
> Photopaint to 1024 x 768 to print 4" x 6" prints, because 10MP are too
> big to upload. I believe that is the correct resolution to use,
> however, a lot of the pictures are pixelated. So now, I'm trying to
> debug what I did wrong. I previously had a Canon Powershot S300 (2MP)
> and never had these problems. I camera takes pix at 72dpi and the
> re-sampled pix have 72dpi too, so I doubt it could be that. Did I
> decrease the resolution too much? Should I make it 1200x1600? When I
> print the images at home (from orignial not-resampled images) I have no
> problem, but the re-sampled images I uploaded are no good. I will try
> various combos of re-sampling to experiment, but I'd like to have an
> idea of what I'm shooting for.
>
> Thanks...



Ben Bowen 11-16-2006 07:30 PM

Re: Resolution, dpi, & pixelation for printing.
 
> If you're resizing only because 10 megs is too big, you might
> try leaving the size alone, and reducing file size by slightly
> increasing the jpeg compression. I suspect you'd like this
> better.


I hadn't considered that. I will give it a shot. Corel allows to adjust
"Compression" and "Smoothing". Are there big differences between the
two that should be known, vis-a-vis file size vs quality?


Cgiorgio 11-16-2006 07:52 PM

Re: Resolution, dpi, & pixelation for printing.
 
Ben Bowen wrote:
> Hi all. I just sent out a bunch of pictures to get processed. They
> were taken with my new Canon A640 (10MP). I re-sampled the pix using
> Corel Photopaint to 1024 x 768 to print 4" x 6" prints, because 10MP
> are too big to upload. I believe that is the correct resolution to
> use, however, a lot of the pictures are pixelated. So now, I'm trying
> to debug what I did wrong.


Hi, Ben,

I've prepared a table showing the paper formats popular in Europe and the
number of pixels required in each direction for printing at 300 Pixels per
inch. 300 is optimum, for large prints which are normally viewed from a
larger distance 150 - 200 Pixels per inch give very acceptable results.

I use Pixels per inch to avoid confusion with the dpi claimed by inkjet
printers, which are a different story.

for conversion to inches divide cms by 2,54

Cms Cms Ratio Pixel Pixel Total Din
v h v h Pixels Format
9 13 1,44 1063 1535 1.632.153
10 15 1,5 1181 1772 2.092.504
13 18 1,38 1535 2126 3.264.307
18 24 1,33 2126 2835 6.026.412
20 25 1,25 2362 2953 6.975.014
24 30 1,25 2835 3543 10.044.020
24 36 1,5 2835 4252 12.052.824
30 40 1,33 3543 4724 16.740.033
40 50 1,25 4724 5906 27.900.056
14,9 21 1,41 1760 2480 4.364.964 Din A5
21 29,7 1,41 2480 3508 8.700.632 Din A4
29,7 41,9 1,41 3508 4949 17.359.833 Din A3



Ken Weitzel 11-16-2006 09:20 PM

Re: Resolution, dpi, & pixelation for printing.
 
Ben Bowen wrote:
>> If you're resizing only because 10 megs is too big, you might
>> try leaving the size alone, and reducing file size by slightly
>> increasing the jpeg compression. I suspect you'd like this
>> better.

>
> I hadn't considered that. I will give it a shot. Corel allows to adjust
> "Compression" and "Smoothing". Are there big differences between the
> two that should be known, vis-a-vis file size vs quality?


Hi Ben...

I don't know Corel, so don't know anything about Corel's "smoothing";
hopefully others here will tell you.

For the time being, just leave your pic full size, increase the
compression until it reaches a reasonable file size, and do some
test prints.

I'd suggest two sets of test prints - one a nice landscape with
lots of sky, the other a portrait type head and shoulders shot.

Take care.

Ken



John McWilliams 11-16-2006 09:21 PM

Re: Resolution, dpi, & pixelation for printing.
 
www.thephotoboard.com wrote:
> hi ben, try downloading yor pics from the cam at 300dpi, and then
> resize to 1800 x 1200px, that would give you an imagesize of 4x6, i
> found a great utility for this type of calculation
>
> http://auctionrepair.com/pixels.html


You don't choose a download dpi, nor even ppi, from the camera. They
will download at however many pixels the camera is set to when the image
is captured. It's often recommended to capture at the highest resolution
your camera will allow; you can always downsize.

And, yes, a 4 x 6 sent to the printer at 300 ppi will measure 1200 x
1800 pixels.

--
John McWilliams

Jim Townsend 11-16-2006 09:31 PM

Re: Resolution, dpi, & pixelation for printing.
 
Ben Bowen wrote:

> Hi all. I just sent out a bunch of pictures to get processed. They were
> taken with my new Canon A640 (10MP). I re-sampled the pix using Corel
> Photopaint to 1024 x 768 to print 4" x 6" prints, because 10MP are too
> big to upload.


OK.. 1024x768 is bad for TWO reasons..

The first reason is that you don't have enough resolution to produce a
good print and the other is that the aspect ratio is wrong.

1024x768 has a ratio of 4:3 and 6x4 prints have a ratio of 3:2. The
printer must crop some of the 4:3 image to get it to fit properly.

I'm not familiar with Corel Photopaint, but it must have a method of
cropping to a constrained value. If you set that to 3 X 2, the crop
square will always have the correct ratio no matter what size you drag
it to.

Once you figure that out, crop the desired 3:2 chunk out of your full
sized image.

Then, sample that crop down to 1800 x 1200 pixels. Now you have an image
that will yield 300 pixels per inch both horizontally and vertically.

300 DPI is the generally accepted resolution for quality prints.

You DON'T have to worry about DPI at all in any step of the way.
That's the processors job. Just make sure you deliver images that are
1800 x 1200 pixels.




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