export from Develop vs print module ?

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tjcadwalader

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My MFT camera has an image size of 4608x3456. I cropped an image to straighten it slightly and ended up at 4540x3027.
I exported a full size JPEG and took that file to a photo shop and had an 8x10 printed. Liked it.
I then I sent that file to MPIX and had a 12x18 metal print made and like the results of that as well. We are considering 16x24 metal print now. This time I went into the print module and set things up to print to a JPEG. I set the paper size to 16x24 and zoom to fit was checked. The file from that export ended up at 4540x3027 ?
2 questions. 1) where are the extra pickles coming from? and 2) which file would give me the better quality, the straight export from the Library/Develop module, or the print module export with the extra pixels?
Thanks for any insight. Printing is something I seldom do. But want to learn more about.
 
Sorry, what extra pixels? You're showing the same pixel size for the Print jpeg and your original crop. Did you mean to type a different number?
 
Oops. Guess I was at this too long last night.

Camera out put is 4608 x 3456
8x10 and 12x18 export from library module was 4540 x 3027
16 x 24 export from the print module was 4800 x 7200

Thanks for catching my blunder.
 
OK, no worries.

In the Print module you've probably got the File Resolution set to 300dpi, and you've probably got Custom File Dimensions set to 16 x 24 inches. So Lightroom then calculates how many pixels it needs in order to meet what you've specified, i.e. (16x300) x (24x300), which is 4800 x 7200, right? But as the file has less pixels than you've asked for, Lightroom will up-scale the image to the required level.

Which is better? I'm not sure, as I don't print very much....if you leave the file at the original dimensions, i.e. 3207 x 4540, then logically the quality if viewed on screen would be better than the upscaled version (though you might be hard pressed to spot the difference). But when it comes to printing, that's another story....if you tried to print the original file to produce a 16 x 24 print, you only have enough pixels to print at 190 ppi, which is obviously less "quality" than if printing at 300ppi. So which is better? And does it matter if you're sending the picture off to an outside lab, if you send the original smaller file they might upscale it themselves in order to print at a higher print density. Something you may need to check out.
 
Lightroom will up-scale the image to the required level.

Which is better? I'm not sure, as I don't print very much....if you leave the file at the original dimensions.

My experience is that the print module in Lightroom does a remarkable job upscaling images. However, it might be asking too much to go from 3027 to 7200, this is almost 2.4 times the size of the 12x18 export.

One other observation, it is odd that both the 8x10 and 12x18 export have the same pixel count. Assuming the longer pixel counts are printed on the longer side: 4540/10 is 454 and 3027/8 is 378.375 (this is really odd), 4540/18 is 252.2 and 3027/12 is also 252.25. Are this numbers correct?

16x24 seems a strange choice, maybe a constrain by the printing lab. For starters, I would not print that much bigger than 16x10; 18 x 12 works out because either the upscaling factor is too small or very few pixels are lost, just under 50 in both cases.

P.S.: I do all my printing through Lightroom's print module even when I am sending to a lab for printing.
 
"One other observation, it is odd that both the 8x10 and 12x18 export have the same pixel count. Assuming the longer pixel counts are printed on the longer side: 4540/10 is 454 and 3027/8 is 378.375 (this is really odd), 4540/18 is 252.2 and 3027/12 is also 252.25. Are this numbers correct?"
I may not have been real clear in my original post. But both the 8x10 and the 12 x 18 were both done from the same export, which was exported as a full size JPEG from the library module. I gave the same file to both labs.
The 12x18 was apparently upscaled by MPIX when they
printed the metal print.
The sizes are based on what the lab offers and was a closer match to my aspect ratio.
I think what I might do is do a 8x10 and 12x18 export from the print module and see what file size I get. We are scrapping the 16x24 idea for now any way.
Thanks for the insights Jim and Modesto Vega

 
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