I want to make Mrs. Devil a gift by blowing up an image to print on fabric. I’d like to increase the image size as much as possible, either to 36” or 72” so I can sew, have sewn, or give it to her to sew something (skirt, shawl, something—what, exactly is TBD).
Here’s what I’ve done. I opened this image (it’s a PNG, the highest resolution I could find so far) in Photoshop. I went to image size and changed its resolution to 150, it’s width/height to 72"; checked scaled styles, constrain proportions, and resampled image (bicubic).
It looks fairly okay at 100% zoom. There’s some noise, but it’s not a jumble of pixels. Is this a fair approximation of how it would print (printer settings aside)?
Also, I see that most printers say their suggested minimum is 150 DPI, but I changed it to pixels per inch. Is that the same/similar or is DPI conversion somewhere else?
[ol]
[li]I took your original image and converted it to a PSD file, so as to not lose anything.[/li][li] I bumped up the pixel rate resolution from 72 to 600 (standard printing resolution for our plotters), so as to not lose the details later. That kicked up the file size to 199 MB.[/li][li] I then increased the image size to 36 inches. But that was going to bump up the file size to 1.2 GB.[/li][/ol]
So I stopped.
If you have access to a plotter, you might want to print a few copies at various resolutions. Just remember that cloth is different than paper so your 150 may be a better choice than my 600.
The actual “resolution” setting in a graphics program does basically nothing. It doesn’t add or remove detail. Literally all that matters is the actual dimension in pixels. What will determine the resolution is the size that the printer prints it out at.
(OK, technically the resolution setting also defines the size if you print it out yourself at “100%”, but that is easy to override.)
And dpi isn’t technically the same as ppi - one measures the resolution of the print output, the other measures the resolution of the image input. You could print a 10ppi image at 600dpi, and you’d just get very crisply defined square pixels 
But if you want to print an image 72" high and the printer requires 150 dots/pixels per inch, you need to make your image 72 x 150 = 10,800 pixels high. That can only be done by upsampling, which will not add any resolution, but it is probably better to do it in Photoshop (which is quite good at upsampling) rather than relying on the printer’s output engine to upsample your image and risk blurring it.
