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Question about render settings.

PostPosted: Fri Mar 19, 2010 4:30 pm
by Mr Moose
I asked this question before, and I only had one reply, so I'm going to ask again as I need to understand this.
In regards to the DPI setting, the default setting is 72 dpi, the last time I asked about this I was told that it didn't matter, I've always set it to 360 because that's what I use when printing to my Epson 3800, but I also set the size % to the size of the print that I want with out resampling later in Photoshop.
So last night I left it set to 72dpi. If I set it to 360 or 72 the width and height didn't change, but
the size did, so I just left it at the default of 72 dpi to see what I'd get in PS.
I rendered my image, opened it in photoShop. Then I went image size to see what I had, the width and height numbers were huge compared to what they were in APP before rendering, something like 20000 pixels at 72 ppi, the size in inches were huge, so now in order to print the image I needed to down sample, I set the ppi to 360 and the height to 16" and let the width fall where it wanted, the printed image seemed soft, lacking fine detail, this was a 6 image pano (two rows of 3)
So it seems that it does MATTER. Why would I want to down sample in PS? There is no documentation that explains what this setting does, or how it should be set. But if I print at 360 ppi wouldn't it be better to render at the ppi that I print at, and at the size I want to print to, with out any resampling later in PS?
Could it be that I just don't understand what resampling in photoshop is all about? please enlighten me if I don't, but I would think that its something that I would want to avoid doing if I didn't need to.
Please, there has to be a answer to this question, I hope I explained this clearly enough.

BTW, shouldn't that setting say ppi (pixels per inch) not dpi. I thought dpi meant dots per inch when printing with a ink jet printer.

PostPosted: Fri Mar 19, 2010 6:07 pm
by [bo]
I'm just going to quote myself:
No matter what DPI you set in the Render Settings window, your rendered image will have the same pixel dimensions.

Here's an example. Say you have an image that shows in the Render window dimensions as follows: 12 000 pixels width and 10 000 pixels height. If you input 72 in the DPI setting, you're going to get a (roughly) 420 x 350 cm image at 72 DPI. If you input 300 DPI (a common number used in printing), you're getting 100 by 85 cm image at 300 DPI. In both cases the pixels that make the image are the same - no more, no less.

PostPosted: Fri Mar 19, 2010 6:34 pm
by hankkarl
Mr Moose wrote:I asked this question before, and I only had one reply, so I'm going to ask again as I need to understand this.
In regards to the DPI setting, the default setting is 72 dpi, the last time I asked about this I was told that it didn't matter, I've always set it to 360 because that's what I use when printing to my Epson 3800, but I also set the size % to the size of the print that I want with out resampling later in Photoshop.
So last night I left it set to 72dpi. If I set it to 360 or 72 the width and height didn't change, but
the size did, so I just left it at the default of 72 dpi to see what I'd get in PS.
I rendered my image, opened it in photoShop. Then I went image size to see what I had, the width and height numbers were huge compared to what they were in APP before rendering, something like 20000 pixels at 72 ppi, the size in inches were huge, so now in order to print the image I needed to down sample, I set the ppi to 360 and the height to 16" and let the width fall where it wanted, the printed image seemed soft, lacking fine detail, this was a 6 image pano (two rows of 3)
So it seems that it does MATTER. Why would I want to down sample in PS? There is no documentation that explains what this setting does, or how it should be set. But if I print at 360 ppi wouldn't it be better to render at the ppi that I print at, and at the size I want to print to, with out any resampling later in PS?
Could it be that I just don't understand what resampling in photoshop is all about? please enlighten me if I don't, but I would think that its something that I would want to avoid doing if I didn't need to.
Please, there has to be a answer to this question, I hope I explained this clearly enough.

BTW, shouldn't that setting say ppi (pixels per inch) not dpi. I thought dpi meant dots per inch when printing with a ink jet printer.

Your last statement shows that you know what dpi/ppi means.

think about this: You can get a 1920x1080 (aka 1080p HDTV) monitor from as small as 19" to as large as 82" (and possibly bigger and smaller).
All these monitors have the same number of pixels on them.
Now, assuming that the monitors are 16:9 aspect ratio with square pixels, the hypotenuse is 18.358. So the 19" monitor is 9.3"x16.56" and the 80" monitor is 40.20"x71.45". The 19" monitor has 115.9 ppi and the 82" monitor has 26.9 ppi.

What should you set the APP dpi setting to to get the best picture on both monitors, knowing that you don't know what your viewers will use?

Answer: it doesn't matter. PPI maters for printing, but monitors display in pixels, not inches. APP outputs in pixels, not inches. Digital files are best measured in pixels, not inches. When you adjust for printing and downsample, make sure you set the ppi to whatever the native resolution of your printer is. Then set the size. Then set the interpolation method to bicubic sharper or bicubic smoother. Then, just before saving, add sharpening for the size you selected.

Try doing exactly what you did before, only don't set the size to 16". Just change the dpi from 72 to 360. When you change the inches, you may also be changing the number of pixels. This may require interpolation which generally results in loss of sharpness.

Note that you said the numbers were huge. Assuming you meant the dimensions in inches, I'll bet they were 5 (360/72) times as big when you selected 72 dpi as when you used 360 dpi.

PostPosted: Fri Mar 19, 2010 6:38 pm
by hankkarl
Mr Moose wrote:Why would I want to down sample in PS? There is no documentation that explains what this setting does, or how it should be set.

Almost forgot to address this question. See http://lmgtfy.com/?q=downsample+in+ps

PostPosted: Fri Mar 19, 2010 7:58 pm
by Mr Moose
Thanks for the reply's.
OK, would it be wrong if I set the dpi in AAP to 360, and in the size column set the slider to the size of the picture I want to print in PhotoShop? I've done it this way, and the rendered pano opened in PS at 360 ppi at the size that I set in AAP. In this case the pano was 50 images, and the file size was very large. The size in inches that I wanted to work with in PS was about 27x17@360ppi. The When moved the slider in the size column in AAP to get that size, I was at about 30%. I assume that reduced the time it took AAP to do the rendering?
Using the above method, I seemed to get what I wanted, but was this correct?

BWT, I tried to render the same file 24x36@360ppi Now the slider is about 88% and smartblend crashed every time.

PostPosted: Fri Mar 19, 2010 9:18 pm
by Mr Moose
hankkarl wrote:
Mr Moose wrote:I asked this question before, and I only had one reply, so I'm going to ask again as I need to understand this.
In regards to the DPI setting, the default setting is 72 dpi, the last time I asked about this I was told that it didn't matter, I've always set it to 360 because that's what I use when printing to my Epson 3800, but I also set the size % to the size of the print that I want with out resampling later in Photoshop.
So last night I left it set to 72dpi. If I set it to 360 or 72 the width and height didn't change, but
the size did, so I just left it at the default of 72 dpi to see what I'd get in PS.
I rendered my image, opened it in photoShop. Then I went image size to see what I had, the width and height numbers were huge compared to what they were in APP before rendering, something like 20000 pixels at 72 ppi, the size in inches were huge, so now in order to print the image I needed to down sample, I set the ppi to 360 and the height to 16" and let the width fall where it wanted, the printed image seemed soft, lacking fine detail, this was a 6 image pano (two rows of 3)
So it seems that it does MATTER. Why would I want to down sample in PS? There is no documentation that explains what this setting does, or how it should be set. But if I print at 360 ppi wouldn't it be better to render at the ppi that I print at, and at the size I want to print to, with out any resampling later in PS?
Could it be that I just don't understand what resampling in photoshop is all about? please enlighten me if I don't, but I would think that its something that I would want to avoid doing if I didn't need to.
Please, there has to be a answer to this question, I hope I explained this clearly enough.

BTW, shouldn't that setting say ppi (pixels per inch) not dpi. I thought dpi meant dots per inch when printing with a ink jet printer.

Your last statement shows that you know what dpi/ppi means.

think about this: You can get a 1920x1080 (aka 1080p HDTV) monitor from as small as 19" to as large as 82" (and possibly bigger and smaller).
All these monitors have the same number of pixels on them.
Now, assuming that the monitors are 16:9 aspect ratio with square pixels, the hypotenuse is 18.358. So the 19" monitor is 9.3"x16.56" and the 80" monitor is 40.20"x71.45". The 19" monitor has 115.9 ppi and the 82" monitor has 26.9 ppi.

What should you set the APP dpi setting to to get the best picture on both monitors, knowing that you don't know what your viewers will use?

Answer: it doesn't matter. PPI maters for printing, but monitors display in pixels, not inches. APP outputs in pixels, not inches. Digital files are best measured in pixels, not inches. When you adjust for printing and downsample, make sure you set the ppi to whatever the native resolution of your printer is. Then set the size. Then set the interpolation method to bicubic sharper or bicubic smoother. Then, just before saving, add sharpening for the size you selected.

Try doing exactly what you did before, only don't set the size to 16". Just change the dpi from 72 to 360. When you change the inches, you may also be changing the number of pixels. This may require interpolation which generally results in loss of sharpness.

Note that you said the numbers were huge. Assuming you meant the dimensions in inches, I'll bet they were 5 (360/72) times as big when you selected 72 dpi as when you used 360 dpi.

Hi Hank,

Just got home. I brought the image that I saved at 72dpi in AAP into photoshop looked at image size. @72ppi it was 73"x 57" the same that it was before I rendered it. What I just learned was, before changing the ppi to 360 in PS, first I have to UNCHECK resample, then change from 72 to 360 with out resampling, so now the size is about 14.66 x 11.44 and the pixel count is the same.
So now I understand what's going on here, I was hung up on what resamlping was doing, I now realize that I DON"T want to resample anything.
This brings up one last question, is it better to do this in AAP before rendering if I don't need such a large image? It made a difference on my 50 image pano using smartblend, there I set AAP to 360dpi and the size slider to about 30% before rendering with no problem, but when set it to 88% to get 24x36 image smart blend crashed every time. So to answer my own question, yes I think it makes a difference.
I hope I made this clear, do you agree?

PostPosted: Fri Mar 19, 2010 9:24 pm
by hankkarl
There are at least two ways to do what you want.

1. render at 100% and downsize in PS. If renders take a long time, this may be a quick way to get a bunch of different output sizes, especially if I had to do a lot of touchup.

2. render at the number of pixels you want in APP. Think of the dpi setting in APP as a calculator--it only tells you (size of pano in pixels / dpi). The advantage here is that APP can use more pixels to create the output--it looks at each input image, where PS will only look at APPs result. APP also has several other interpolaters that are better than bicubic. And we all know that the smaller the rendered image, the less likely APP is to crash.

So I'd render at the size I needed the output even if I have to render many times (but I have a fast machine) if APP gave a great result. Otherwise, if I had to touch thing up (e.g. remove ghosts) and needed a couple of different output sizes, I'd render once and downsize in PS. If you really care, there may be a PS plugin that does a better job of downsizing than PS does. Note-always render the biggest pano you need, its better to downsize than upsize.

Also, you need to check your printer's resolution. Many Canon printers are a multiple of 300, many Epson printers are a multiple of 360. Use that number (300, 360 or whatever) for the dpi so that the printer driver does not interpolate your image.