Is it not ideal to save image as PNG for printing?

Question

So the scenario: I want to order a print of one of my images. It is a special image and will be relatively large (a couple of metres) so I want it to be perfect as possible.

I have the RAW file, however the printing service only takes PNG, JPEG, and TIFF. So PNG is lossless, why shouldn't I export my RAW as it then? I have searched the web, and the only issues I can find is "JPEGs load faster on web pages and take up less storage on disk" - which is completely irrelevant for my use. Surely it's better to export as PNG if I have enough storage so I get absolutely no compression - the same for other lossless formats as well?

If someone can say why I shouldn't can you explain. Thank you :)

Answer 1

Yes, PNG is theoretically better than JPEG in preserving the ultimate image quality, but in practice this is the kind of exactness we don't really see, especially in print, where the physical properties of the paper and ink technology limits what can be achieved.

For convenience, just stick with the universally accepted JPEG and be happy with smaller file sizes.

But yes, sometimes the PNG would be preferable:

• non-photographic synthetic images, like charts, graphs, fine print - the JPEG kind of compression is not designed for such cases
• anything that is repeatedly being saved, reloaded, edited - because unlike PNG, in JPEG the image quality is degraded on each cycle

Answer 2

Avoid PNG-8 for photo images (it is for graphics with few colors), but PNG-24 is very good choice for photo images. Better than JPG for quality, but will be a much larger file than JPG.

PNG always compresses, and compresses reasonably well, smaller than TIF LZW, but not nearly as small as JPG. Both PNG and TIF LZW are lossless compression, meaning there is simply no question about losing image quality. Both are perfect for photo images. But their larger file size prevents their mass popularity (except top end commercial prepress practices will insist on them, for quality reasons).

JPG will be a much smaller file, with size and quality dependent on JPG Quality setting, but JPG is lossy compression (NOT lossless), and even the very best JPG is still JPG. Best JPG can be pretty good but is Never lossless. JPG can be small because it is lossy, meaning not so concerned with lossless preservation of all the details. High Quality JPG can be pretty good and adequate, and pretty small, but never lossless.

The mass market photo print shops are used to JPG, and they are concerned with their storage space too, and the smaller JPG is of course fastest on the internet transfer too, but many of the good shops will accept PNG or TIF too. The only question is that you might ask them first if they will accept PNG files, otherwise PNG would be great. But PNG-24, and Not PNG-8 for photos.

Answer 3

You cannot just export a raw to TIFF, PNG or JPEG, you'll have to do some treatments, for a number of reasons. But you seem more interested in the differences between the different file formats.

I'd stay away from TIFF, as there are just too many 'dialects' for that format, and in this context, it has no advantages over the other formats.

For the choice between png and jpeg, it's less clear. While indeed PNG is lossless (and can be 16 bits/channel), for printing that's not really a problem, as a high quality jpeg is visually indistinguishable from a png (high quality: 90%, don't bother with the highest settings). At the same time, the jpeg will be a lot smaller (10x isn't unusual). For my equipment, 16-bit/channel png would take about 110 Mb, 8-bit/channel png 42 Mb and jpeg 7.5 Mb.

The difference only gets visible after you have to re-encode a jpeg several times; or when you go to lower quality levels.

But you really should discuss with your printer how to prepare your file. If you are indeed going to order a print of several meters, they should be able and willing to help you (if not, I'd go and look for another printer, given the price of such prints). There are other issues to consider as well, like what colour space should you use, how to sharpen for such sizes, etc.

Answer 4

Isn't PNG an RGB only format? That would not be ideal for any kind of print work, which is exclusively a CMYK process. TIFF is lossless and the preferred format for large print images, at the cost of file size (TIFFs are big). JPG will work for print, but is lossy. So every time it is resaved, some data is lost, eventually causing reduced image quality. I'm kind of shocked by people recommending PNGs for printing. If you have any other option, pick the other option.