I'm intending to create some photographic images for printing. They'll be used to hang on a wall but will be quite large (80 - 100cm square). Obviously I want the quality to be as high as possible, so I'm guessing I should aim for 300dpi but the file sizes are so huge, they're not possible to email. Can anyone advise me? I really have a problem with handling large file sizes to keep the best possible quality.

Any advice would be gratefully received...!

Many thanks, Rick

  • 1
    Nobody can advise you as what you want is either perfectly defined or impossible. "As high a quality as possible" means lossless. 300 dpi is a choice and is higher than needed for fine art printer according to many experts. You need to set some bounds re what is acceptable or file sizes you can accept. You don't say what your source is. 80 cm square ~= 32" square at 300 dpi =~ 90 megapixel. Do you REALLY have a 90 mp source? – Russell McMahon Jul 4 '12 at 8:49
  • Sorry. I need an idiot's guide. The images have been produced on a Nikon D3100... – Phatsnapper Jul 4 '12 at 9:03
  • There are some useful tweaks to JPEG. Try JPEG2000 saving at various compression rates and file sizes. See what seems to work acceptably. Irfanview free here allows you to set a target file size for a range of file formats. What fle sizes have you got and what is acceptable.? – Russell McMahon Jul 4 '12 at 9:10
  • There's a well-known formula: a picture is worth a thousand words. Those thousand words should fit in a text file of 6...10 kB, which, according to the formula, is lossless. So, just send a description of the picture, there's no way you can beat that size/quality ratio with any JPEG compression. – Imre Jul 4 '12 at 20:13
  • Many thanks Russell. I use a mac and Ifranview's a windows app. No worries. Thanks for your help and advice. Will try JPEG2000. I realise that file size is a bit like 'how long's a piece of string?' - depending on the detail of the image, pixel information etc but it's an area I really struggle with. I once sent a file (on cd), to be printed approximately 1 metre square and all the designers laughed at the size of it (I mean mbs), It was the size of a house and nearly crashed their machines!! Thanks again. – Phatsnapper Jul 6 '12 at 8:44

There is an easy to get the highest possible quality and email-size from the same photo: Make two files. That is what all the pros do. Actually, they probably create more. There is no reason why one file would have to the ideal for all uses. Actually, that is impossible.

Lets say you shoot with a Nikon D3100 and you got a 7.1 MB file. This is the largest and highest quality JPEG I have produced from the D3100. This is your high quality version. This is the one you print from. To send it to a print shot there are tons of ways to do it: FTP (Most high-end print shop accept FTP), Optical Disk (I use a Rewritable disk which I keep bringing with new images), USB key, file sharing service (DropBox and the like), etc.

On some email platforms, you can even email this (up to 10MB is common now) directly but your friends might not want to wait that long to see your shot. It's too big for their screen anyways. When you want to share you create a lower-resolution version which is still high quality. Adobe Lightroom calls the Export and you can set the resolution, quality and even file size. It can do it in batch too which is great. Photoshop has Save For Web where you can also control the size and quality with a preview of what it looks like. You can also use command line tools like nconvert.


I would recommend that you don't email huge files, when there are so many free and good alternatives to transferring them.

Just upload the files to Dropbox or something similar and simply send the links to the files to the recipient. Much better, and also saving about a quarter in transferred bytes, as the photos don't have to be base64 encoded for email transfer.

  • This is exactly the right answer. You put uncompressed files in an online storage location shared with the intended recipient and then email them the location and instructions to notify you when they have downloaded their copy. That way, you can remove the file(s). – Steve Ross Jul 4 '12 at 20:28
  • Definately! I'll go down that road I think and read up a bit more about compression and it's effects.. Thanks Steve and leberwurstsaft (love the name!!) – Phatsnapper Jul 6 '12 at 9:03

Do you really need to e-mail them? It'd be best to transfer the entire file, and they can't be that big, even losslessly compressed.

If you do need to get them smaller without quality loss, using JPEG is the normal approach, and to do that best, you need to understand what JPEG compression does to an image. Take a look at


(That has some pixel-peeping examples which are relevant even when not using Pentax cameras.)

Armed with that knowledge, you can try different levels of compression and then look to see if they've caused any visible "damage".

But still, my advice is to find some way to transfer your large, top-quality files to the print service.

  • Thanks mattdm. Great help and yes, I do need to read up a bit more to understand a bit more about what happens with compression.. – Phatsnapper Jul 6 '12 at 9:00

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