I have been asked to create large size images to be the printed with a good quality to look at. The images could be with dimensions of 1 meter in height or width, but even larger. I must create these large images starting from maps that are created online ( I do not say the source to avoid advertisement) and those images can be only downloaded as jpg images. The dimensions of the maps, in pixels, can vary depending on the map but each pixel corresponds to 10m in the map, while the horizontal and vertical DPI resolution is 96. In the layout composer of QGIS I have tried to set the sizes of the image even at 2m and then I saved the image as a tiff with dpi = 300, starting from an image of 1456x611 pixels. I obtained an image of 23622x9502. Of course the file is quite big, but this is not the problem. What I wonder is if the printed image could come out pixelated or with a good printing quality. And which settings can actually give a good print quality to be used in QGIS when images should be so large
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if your source data is from online maps they are much lower resolution for a good reason (faster loading in a web browser). The best way is download or create the higher resolution images locally. When worked in this sector there were 2 products 72 dpi for online and 300 dpi on our local network printing to a 60 inch plotter.– Mapperz ♦Commented May 2, 2019 at 23:58
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Yes, the reason of low resolution for download is clear. What I mean is if a 300dpi resolution for a printed image coming from a jpeg is enough when the printed image is supposed to be of large sizes. I have no experience on that.– TelcoGISCommented May 3, 2019 at 0:01
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1This may not answer your question, but I hope it adds to your body of knowledge... Using QGIS 3.6 Composer. (Layout? I forget, away from computer!) I've created ~ .6 X .9 meter pdfs containing a web map (If I recall, OSM) as well as local shape files, @ 450 dpi. Although the resulting file sizes were dozens of GB in size, the resulting prints were spectacular! Yay QGIS! However, error messages would appear if I tried to print @ higher dpi - I had to experiment to find an upper dpi value that would work. I suspected that some sort of upper limit was being reached. Good luck!– Stu SmithCommented May 3, 2019 at 1:14
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this info are really useful! the point that most worries me is to know which dpi resolution is necessary for a good print quality when the print size is 1m or more, and if QGIS works fine when creating HR images for print , starting from a JPEG image– TelcoGISCommented May 3, 2019 at 1:32
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1@Antonio Please report back with your findings, as they will be useful for the entire community!– Stu SmithCommented May 3, 2019 at 2:47
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