I have a number of pics that I will send to Ofoto for developing. They are all 1280X960. All will be 4X6. Because it takes forever to upload I was thinking of reducing to around 800X600. Will I lose significant quality by doing so? If not, should I edit before or after downsizing? Thanks, Steve
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Image Size
- Thread starter NVSteve
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dmlove
Senior Member
What is the file size (in megabytes) at the original picture size?
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Davia
C-700
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Davia
C-700
pbase supporter
http://www.pbase.com/dmlove
Sorry had to leave for a while. The files are generally about 500kb.
B
BobTrips
Guest
I wouldn't do it. I'd bit the bullet and send the larger files.
If you downsize the files you will be printing at less dpi.
For example, taking the long dimension at 800 pixels spread over 6" you will be printing at about 133 dpi. At 1280 pixels spread over the same distance you will be printing at about 213 dpi. That will probably be quite noticable.
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bob
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pictures from Thailand and Myanmar(Burma)
David SL
Senior Member
I originally had a nice post long response to this, but when I tried to preview it the site brought me back to the forum list page, of course trying to hit "back" on my browser didn't bring back all my post text... sigh this happens a bit more than I'd like unfortunately..but here goes ..again.
Assuming Ofoto prints at 300dpi on their prints. A 4 x 6 would optimally need no more than:
4 x 300 = 1200
6 x 300 = 1800
1800 x 1200 pixels. So looking at your starting dimensions you are already not going to pull out all the res. that the print is capable of giving you assuming it's a 300dpi print. (The photofinisher I use photobox.co.uk uses 300dpi Fuji Frontier printers for all their work that's why I use it as a guide, ofoto might use something else with a different res. so you can adjust these calculations accordingly if so.)
In fact at your dimensions above the image won't be proportional to the print. So let's find the proportional dimensions, in other words the dimensions after cropping that will allow a full 4 x 6 print.
1200/1800 = x/1280
x = 853.3
Proportional dimensions: 1280 x 853.3
: assuming no cropping or scaling on the part of the photofinisher to fill the frame your print will be:
1280 dots/ 300 dots per inch = 4.26 inches wide
853.3 dots/ 300 dots per inch = 2.84 inches high
Here's how it would look relative to the 4 x 6 print surface:
After scaling the 1280 x 853.3 image to fill the 4 x 6 print, you can find the effective resolution to be:
1280/6 = 213.33 dpi
853.3/4 = 213.33 dpi (they are equal because the pixels are square)
:The reason we scale the image is that most photofinishers do if it doesn't contain enough res. to fill the print frame at the rigs dpi rating (assumed 300dpi in this case, where we are assuming one pixel maps to one dot which may not be the case). The usual method is bicubic interpolation, and that's the one I used for the crop below which shows how a 1 inch square region of the image would look after the entire image is scaled to 4 x 6 size:
looks good, but we want to see how the 800 x 600 sized image will compare to this, first we have to find the proportionality dimension so that it fits on the 4 x 6 with little to no cropping like before.
x/800 = 1200/1800
x = 533 pixels
800 x 533 pixels
Below, is an image showing the dimensions you desire as it would display on the 4 x 6 print if printed without scaling by the photofinisher, also shown (in green) are the pixel dimensions for both this reduced image and previously calculated original image size and (in red and blue) is shown the dimensions in inches of each relative to the entire 4 x 6 print surface.
You can see that your 800 x 600(533) image is very small without scaling, it looks as if it will need to double in size to fill the 4 x 6 print this will be a source of blurring as detail is sized up. Here's a crop of the same 1 inch square region of the print after this smaller image is scaled to fit the 4 x 6 print:
and the original again to compare closely:
The difference is obvious, your 800 x 600(533) 4 x 6 print will show its softness relative to the full size 1280 x 960(853) image size. Most of the softness comes in when the image is scaled up, most likely the photofinisher will use a single pass of a bicubic interpolation routine. It's been discovered that a series of passes yields a sharper image over one which is why it's always always better to size your images so that they match the resolution of the print device at the desired print size. (The photofinisher will do one pass as in my example above, but you can right size it using multiple passes then send it for printing preventing as much as possible, scaling on their end.) As I stated earlier for a 4 x 6 print at 300 dpi that is : 1800 x 1200 pixels which even your starting image is already below so be prepared to suffer in detail and sharpness the smaller below this dimension you wish to send, conversly the larger dimension will require longer download times. At the smaller size your download speed will increase it's up to you weather the detail lost in the prints is acceptable.
You should always edit big, you have more fidelity to make your adjustments, when its perfect then size down.
Hope that helps you out.
Regards,
--
mpeltier
Forum Enthusiast
David,
I have to say that is probably one of the most informative and useful posts I have read here in a while. And I wasn't even looking for any info on the subject and I learned something new and it made sense. Thanks
Mike
I have to say that is probably one of the most informative and useful posts I have read here in a while. And I wasn't even looking for any info on the subject and I learned something new and it made sense. Thanks
Mike
I originally had a nice post long response to this, but when I
tried to preview it the site brought me back to the forum list
page, of course trying to hit "back" on my browser didn't bring
back all my post text... sigh this happens a bit more than I'd
like unfortunately..but here goes ..again.
Assuming Ofoto prints at 300dpi on their prints. A 4 x 6 would
optimally need no more than:
4 x 300 = 1200
6 x 300 = 1800
1800 x 1200 pixels. So looking at your starting dimensions you are
already not going to pull out all the res. that the print is
capable of giving you assuming it's a 300dpi print. (The
photofinisher I use photobox.co.uk uses 300dpi Fuji Frontier
printers for all their work that's why I use it as a guide, ofoto
might use something else with a different res. so you can adjust
these calculations accordingly if so.)
In fact at your dimensions above the image won't be proportional to
the print. So let's find the proportional dimensions, in other
words the dimensions after cropping that will allow a full 4 x 6
print.
1200/1800 = x/1280
x = 853.3
Proportional dimensions: 1280 x 853.3
: assuming no cropping or scaling on the part of the photofinisher to fill the frame your print will be:
1280 dots/ 300 dots per inch = 4.26 inches wide
853.3 dots/ 300 dots per inch = 2.84 inches high
Here's how it would look relative to the 4 x 6 print surface:
After scaling the 1280 x 853.3 image to fill the 4 x 6 print, you
can find the effective resolution to be:
1280/6 = 213.33 dpi
853.3/4 = 213.33 dpi (they are equal because the pixels are square)
:The reason we scale the image is that most photofinishers do if it doesn't contain enough res. to fill the print frame at the rigs dpi rating (assumed 300dpi in this case, where we are assuming one pixel maps to one dot which may not be the case). The usual method is bicubic interpolation, and that's the one I used for the crop below which shows how a 1 inch square region of the image would look after the entire image is scaled to 4 x 6 size:
looks good, but we want to see how the 800 x 600 sized image will
compare to this, first we have to find the proportionality
dimension so that it fits on the 4 x 6 with little to no cropping
like before.
x/800 = 1200/1800
x = 533 pixels
800 x 533 pixels
Below, is an image showing the dimensions you desire as it would
display on the 4 x 6 print if printed without scaling by the
photofinisher, also shown (in green) are the pixel dimensions for
both this reduced image and previously calculated original image
size and (in red and blue) is shown the dimensions in inches of
each relative to the entire 4 x 6 print surface.
You can see that your 800 x 600(533) image is very small without
scaling, it looks as if it will need to double in size to fill the
4 x 6 print this will be a source of blurring as detail is sized
up. Here's a crop of the same 1 inch square region of the print
after this smaller image is scaled to fit the 4 x 6 print:
and the original again to compare closely:
The difference is obvious, your 800 x 600(533) 4 x 6 print will
show its softness relative to the full size 1280 x 960(853) image
size. Most of the softness comes in when the image is scaled up,
most likely the photofinisher will use a single pass of a bicubic
interpolation routine. It's been discovered that a series of passes
yields a sharper image over one which is why it's always always
better to size your images so that they match the resolution of the
print device at the desired print size. (The photofinisher will do
one pass as in my example above, but you can right size it using
multiple passes then send it for printing preventing as much as
possible, scaling on their end.) As I stated earlier for a 4 x 6
print at 300 dpi that is : 1800 x 1200 pixels which even your
starting image is already below so be prepared to suffer in detail
and sharpness the smaller below this dimension you wish to send,
conversly the larger dimension will require longer download times.
At the smaller size your download speed will increase it's up to
you weather the detail lost in the prints is acceptable.
You should always edit big, you have more fidelity to make your
adjustments, when its perfect then size down.
Hope that helps you out.
Regards,
--
David SL
Senior Member
Mike,
You are quite welcome, only giving back what I've learned in these excellent forums over the last 1.5 years.
Regards,
You are quite welcome, only giving back what I've learned in these excellent forums over the last 1.5 years.
Regards,
--
Thank you David. Your reply was very helpful. I learned alot. Steve
You are quite welcome, only giving back what I've learned in these
excellent forums over the last 1.5 years.
Regards,
--
Michael Meissner
Forum Pro
One thought would be to reduce a couple of pictures and send them in with the current batch to judge what the quality is. It is likely different on different printers.
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