I've made several collages and wanting to print an 8 x 10 I'm constantly told "there will be a resolution" problem. I guess I'm ignorant of what happens when I reduce the "huge" jpg to a smaller size. I just assumed that the smaller the picture the more pixels - apparently NOT! How do I correct this? Thank you.

  • 1
    How are you reducing the "huge" jpg? – mattdm Apr 28 '18 at 13:42

The smaller the picture is resampled, the fewer the pixels.

Image size is dimensioned in pixels. 24 megapixels might be 6000 x 4000 pixels (6000 x 4000 = 24 million). In uncompressed data, there are 3 bytes per pixel (the most common normal 24 bit color), but JPG compresses the file significantly smaller.

To print 8x10 inches at an optimum 300 pixels per inch is a size of
(8 inches x 300 dpi) x (10 inches x 300 dpi) = 2400x3000 pixels.
Fewer than that is less than optimum.

300 pixels per inch is optimum (more won't help color photo printing).

200 pixels per inch might be acceptable quality, but not best.

100 pixels per inch is considered too few pixels.

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    Depending on the print tech and media, the level of detail, and degree of close scrutiny, it's not necessarily true that more than 300ppi "won't help". – mattdm Apr 28 '18 at 13:43
  • Also note that typically, pixel is not equivalent to byte. Given a typical RGB image with no compression, 24 megabytes is closer to 8 megapixels, or something like 3465x2310. Unless you were referring to a monochrome image... – twalberg Apr 28 '18 at 16:56
  • mattdm, agreed, there are other situations (but Only other in JPG files is grayscale). I was assuming RGB JPG photos. Lineart printing is better at 600 dpi, but that is not JPG. twwlberg, yes, I did mispeak, I meant 24 megapixels, and did equate it to 6000x4000 pixels. Edited now. – WayneF Apr 28 '18 at 19:05
  • Many printers have a base resolution of 360 ppi, or even 600 or 720 ppi. For such a printer, an image that will yield higher resolution than 300 ppi will show more detail (i.e. with a 720 ppi printer an 8x10 inch print made from a 5760x7200 pixel image will show more detail than a print made from a 2400x3000 pixel image). – Michael C Apr 28 '18 at 20:02
  • @MichaelClark True. And it's not just detail, Most printer driver interpolate between their native resolution by using nearest neighbor, a relatively crude technique. While rare, I've seen instances where printing at a different (higher or lower) resolution than the native printer can create moire. Striped shirts, and regular patterns such as building facades are more likely to show it. Even then it's quite rare and won't show up except on the sharpest of images. But if you run across it resample the image before printing. – doug Apr 29 '18 at 3:23

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