hi all, I have some old images that were shot in JPEG with 8 Mega pixels 3456 X 2304. The Export setup in Lightroom allows users to export to any sizes and any resolutions they choose to. As the images were shot in JPEG, what is the limit that an 8 Mega pixels JPEG image can be exported using Lightroom feature without compromising the quality of the image being pixelized?
I ran an experiment exporting an 8 mega pixels image with long edge = 152.4 cm, resolution = 300 DPI. Lightroom generated a JPEG file with dimensions of 18000 x 12000. I looked at the file. How is it possible? Generating a JPEG file with dimensions of 3456 x 2304 to another JPEG file with dimensions of 18000 X 12000?
It is doing exactly what you asked. 152.4 cm = 60 inch. At 300 pixels per inch, the long edge thus becomes 18000 pixels long. If you don't want Lightroom to upscale check the checkbox "don't enlarge" in the export dialog.
That said, it should gracefully upscale and you should not notice obvious pixelization doing this. Lightroom uses smart scaling algorithms depending on whether you scale up or down and it should just look unsharp if you zoom in all the way on the exported image as there was only as much detail as you had in the original file. It should not look blocky and pixelated.