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04/20/2005 03:21:21 PM · #1 |
Having decided to print my POD images I spent some time editing them to be printed at a local printers,,,
formatting them to be printed.
I have not printed off many images so am a little of a novice here
When I opened the original jpeg usinh P'shop 7 it opened at 180 pixels per inch
width = 2048 pixels
height = 1536 pixels
doc size
width = 11.378 inches
height = 8.533
I understood that for printing a better DPI was 300
so I resized to 300DPI and got the following
width = 3413 pixels
height = 2560 pixels
doc size
width = 11.378 inches
height = 8.533
this surprised me as I expected the physical size to reduce to accomodate the additional DPI.
So this poses me to ask some questions.
1. Did I do this right.
2. will the image quality be ok to print 6*4
3. should I be doing something different
Ian |
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04/20/2005 03:32:12 PM · #2 |
DPI, as you probably know, should correspond with the DPI of the equipment your printer uses. I suggest you call him and ask what DPI his printer printer prints at.
When you adjust DPI in Photoshop, it also, as you noticed, alters width and height. But you can simply re-enter the w/h values you desire after you've made a DPI adjustment. This does NOT constrain.
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04/20/2005 03:36:17 PM · #3 |
Originally posted by zeuszen:
DPI, as you probably know, should correspond with the DPI of the equipment your printer uses. I suggest you call him and ask what DPI his printer printer prints at.
When you adjust DPI in Photoshop, it also, as you noticed, alters width and height. But you can simply re-enter the w/h values you desire after you've made a DPI adjustment. This does NOT constrain. |
Thanks for the imput,
I was a little uncertain here... |
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04/20/2005 04:00:47 PM · #4 |
Originally posted by Artan:
Having decided to print my POD images I spent some time editing them to be printed at a local printers,,,
formatting them to be printed.
I have not printed off many images so am a little of a novice here
When I opened the original jpeg usinh P'shop 7 it opened at 180 pixels per inch
width = 2048 pixels
height = 1536 pixels
doc size
width = 11.378 inches
height = 8.533
I understood that for printing a better DPI was 300
so I resized to 300DPI and got the following
width = 3413 pixels
height = 2560 pixels
doc size
width = 11.378 inches
height = 8.533
this surprised me as I expected the physical size to reduce to accomodate the additional DPI.
So this poses me to ask some questions.
1. Did I do this right.
2. will the image quality be ok to print 6*4
3. should I be doing something different
Ian |
When changing the dpi in photoshop uncheck the resample box so the actual number of pixels does not change (unless of course you want it to)
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04/20/2005 04:14:32 PM · #5 |
Look at the data here:
When I opened the original jpeg using P'shop 7 it opened at 180 pixels per inch
width = 2048 pixels
height = 1536 pixels
doc size
width = 11.378 inches
height = 8.533
I understood that for printing a better DPI was 300
so I resized to 300DPI and got the following
width = 3413 pixels
height = 2560 pixels
doc size
width = 11.378 inches
height = 8.533
What you've done is ADDED pixels to the image. Your original image contained 3 1/2 million pixels, roughly: 2048x1536=3,145,728. Your resized image contains roughly 8 3/4 million pixels: 3413x2560=8,737,280. You have more than doubled the number of pixels in the image!
Now, these pixels were not part of the original image, so your software (Photoshop in this case) had to create them, and it did so by a process called "interpolation". If you used the default setting, it was done by "bicubic" interpolation. Interpolation algorithms measure the "value" of surrounding pixels and then insert between them new pixels that in some way represent an average of the surrounding pixels.
If your shot was a single-color shot of, say, a sheet of yellow paper, evenly illuminated, the interpolation would be perfect and there would be no degradation of the resultant, enlarged image. On the other hand, if your image was a finely detailed shot of a multitude of thin, diagonal lines, the interpolation would cause a certain degree of jagginess down the sweep of these lines, and it would be less satisfactory.
One way around the problem is to use what's called "step interpolation", which involves increasing the size of the image many times, in very small steps, until the desired size is reached. There is very sophisticated software out there to do this (Genuine Fractals is one of the best regarded) and there are Photoshop actions available to do it also. Fred Miranda sells one for $19.95 (I think) that works extremely well. According to many people, the results of the FM action are better than those from Genuine Fractals, at a fraction of the cost.
However, when you go to resize in Photoshop you'll notice there's a checkbox for "resample image". If the box is checked and you type in "300" in the dpi field, the resultant image will be interpolated so that it has more pixels in the same X by Y inch size as the original. If you uncheck the resample image box, the number of pixels on each dimension will remain unchanged, but the X by Y inch dimensions ("print size") will change, becoming smaller and smaller the higher the pixels-per-inch count rises.
In other words, if you change the ppi number without resampling the image, all the information in the image remains unchanged; only the output dimension is changed. When you resample, you physically change the information in the image, either removing information as you downsize for the web or adding information by interpolation as you upsize for printing.
So what I do when I prepare an image for printing is first define it (without resampling) at the ppi supported by my printer. Then I look at the X by Y inch dimensions and decide if I want it bigger than that. If I DO want it bigger, I use step interpolation to "grow" the image in small increments in order to preserve as much visual acuity as possible.
Sorry if this is more than you wanted to hear :-)
Robt.
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04/20/2005 04:42:18 PM · #6 |
Bear, thanks for the post! I'd be very interested to read more details on how you do your step interpolation in Photoshop, if your fingers aren't too cramped from your last post.
:-) |
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04/20/2005 04:48:35 PM · #7 |
Originally posted by bear_music:
What you've done is ADDED pixels to the image. .........
..............................
Sorry if this is more than you wanted to hear :-)
Robt. |
Thanks for the info..... |
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04/20/2005 04:56:23 PM · #8 |
Originally posted by Strikeslip:
Bear, thanks for the post! I'd be very interested to read more details on how you do your step interpolation in Photoshop, if your fingers aren't too cramped from your last post.
:-) |
You check the Resample box. In the area where it lists the dimensions, change the pop-up to "Percentage" instead of inches or whatever it's at -- the value should change to 100. Set that number to 105 and click OK; the image is now 105% of the original size (at the same resolution). Repeat increasing in 5% increments (some people use 10%) until the dimensions are as large as you want, or the image quality degrades too much. |
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