Resizing images for large format prints

[ATurner]

I need to resize my photos to a 16x20 print, for example, but keep them at 300 dpi.

When I use the Resize tool, it either distorts the image (because I turn off the maintain ratio) or it won't let me do a 16x20. Flat out WON'T let me do it.

So then I used the crop tool, clicked Specify Print Size so I could change the dimensions to 16x20, but then it lowers my resolution signicantly....so much so that as a final jpeg file (I start out with a tif), the size is severely condensed -- so small that I couldn't even get a 4x6 out of it.

What am I doing wrong?

[df]

You can't take an image that doesn't have a 4:5 ratio and resize it to 16x20 without distortion. It's just the way things are, but you've figured that out.

The crop tool shows you what the dpi will be after the crop. It's not lowering the dpi, you by specifying 16x20 are providing the final dimensions and it's just showing you the pixels that you have. No downscaling is happening.

Can you tell us the dimensions that you're starting with? That would help alot.

Try cropping to 16x20 (or 8x10 or 4x5, these are all the same 4:5 ratio), then resizing to 16x20 @ 300 dpi. The quality may not be there to provide a decent print from though, it sounds like you just don't have enough pixels. Specify width and height (16 inches x 20 inches) and resolution (300 pixels per inch). Make sure Advanced Settings is checked, Lock Aspect Ratio, Resample Using Smart Size. This will give you the best resolution while upsizing without jumping through more hoops.

Hope this helps.

[LeviFiction]

As, Df, said we could use more detailed information on your image. Pixel dimensions. Current print size and dpi. How low the DPI drops with the crop you tried to make.

It should also be noted that upsampling traditionally is terrible. So if you can avoid it at all that would be best.

As for the dpi, don't be so restrictive. The actual requirements for a print are based on distance the observer is going to be from the image. Obviously if possible you never want to go below 150dpi (useful for if the viewer is a yard/meter away from the image at the very least) but 267 in most cases is more than acceptable. I have a friend in the printing business and he's always told me that between 267 and 300 is perfect for people holding the image out to arms length.

Always use a dpi that will get you close to what you want, for the distance the viewer will be from the image, with minimal upsampling (creation of new pixels that didn't exist).

But if you could tell us the current size (inches and dpi) and the pixel dimensions might be able to give better advice. I'm pretty sure Df could. Defiantly knows what he's talkin' about that one.

Now, like they said, if your aspect ratio of your current image is not the same as that of 16x20 then the crop tool will allow you to crop of parts of the image you don't need and get the aspect ratio you want. Though it will change the dpi settings but this isn't a big deal. You may end up having to use a combination of Crop and Resize or Resize and Canvas size. Because no single method will give you exactly what you want.

Quick review of these two methods:
Crop and resize - crops the image to the aspect ratio you want, then resizes using the dpi you want. Will most likely upsample creating a blurry gunky image.

Resize and canvas size - resizes the image as close to 16x20 as it can get without distortion then adds a border around the image to fill up the required space for those extra pixels. Due to possible upsampling it will again create a blurry gunky image.

[pdxrjt]

Well, not sure I can add much to Levi's answers, but there are basically 2 issues you bring up--resizing is one and saving resolution of the file is the other. Regarding resizing....as Levi states, if the image isn't in the proper ratio, resizing to 16 x 20 will cause distortion.....so you can use image info to check the current size of the file and dpi. If it isn't in the proper ratio, use the crop tool..... although 4x5 or 8 x 10 is the proper ratio, you could create and save a 16 x 20 as a reminder. If the file is in the proper ratio, using the resize function should let you do what you want.... you may already have found the advanced setting which let you unlock the ratio etc. (which will cause distorion.) So I'm not sure how the resize tool "won't let you" do a 16 x 20. That sort of tells me that the file is not currently in the proper ratio or the resize tool is not unlocked. (Assuming you don't want distortion, get it in the proper ratio first using crop or other methods.) BTW, if you click on help when the resize tool is open, your web browser will take you to a nice PSP file about the effects of resizing including what happens to your pixels.

As to picture quality. Part of that depends on the size of the original image. An older point and shoot camera isn't going to make an image you can successfully blow up to 16 x 20. Similarly, if you have a nice 10 meg file but you are trying to blow up a tiny detail....you may well be out of luck trying to make a 16x20. If you are shooting with something large enough to make a good 16 x 20 image consider your saving options and how you work on the picture. I don't work this way myself, but if you resave jpegs during the course of your workflow, I've been told it degrades the image. If you made a copy of your original tif as a tif (--never work on the original, right?) then saving it shouldn't degrade the image. After you get it the way you want, you can resize then try saving the resized image using the jpeg optimizer. Set the compression to 1 for best results. Again, this will only work if the image is large enough to stand being blown up. Check it using image information.

Good luck