Wednesday, March 17, 2010

Image file formats for artist bloggers

This post is about which image file formats artists and bloggers should use for what - and why.

This post is about image file formats for artists and bloggers. I'm writing it to remind myself of the basic characteristics of different formats because I'm in the middle of getting to grips with a new graphics program. This means I'm revisiting a lot of the basics as well as learning new stuff. It's reminding me of how much there is to learn when you start to use images on the internet.

A picture of a flower compressed with successively higher loss JPEG compression ratios from left to right (source - wikipedia)

I'll start with my basic aide memoire - it goes from the simplest to the more complex.

Which file formats should I use for what - and why?

Very basic simple images for the internet
What you want: something very simple in colour terms and quite possibly very small eg an avatar
  • use a GIF file (Graphics Interchange Format) which is limited to an 8-bit palette, or 256 colors making it very suitable for very simple graphics files
  • It can render the image exactly and keep the file size small so long as the colour is one of the 256 colours.
Images for the internet (website / blog / gallery site)
What you want: images which look good on screen and load quickly. They don't need to be big or to be capable of being printed.
  • always use a compression format (eg jpeg or gif) if you want an image to load quickly
  • a typical jpeg file is still too big for the internet so needs to be made web-ready
  • create a web-ready jpeg through compression to (say) no more than a 100KB file - this means that they look good on the internet; are useless when printed out (ie protects copyright concerns) and they load quickly and do not deter people from visiting your website or blog
  • reduce the size of the image (ie reduce the pixel dimensions) to create a web-ready file. I typically make the longest side no more than 500 pixels and very rarely use anything over 1,000 pixels on the internet
  • reduce the number of dots per inch (dpi) to make a smaller file. This is different from reducing the dimensions. 72 dots per inch (dpi) is a good standard for web-ready jpeg files. (It's the one I always use) A lower dpi can lead to more pixelated images. A bigger dpi can create large files which take longer to load
Images for entering art competitions
what you want: images which look excellent and comply in every way with the technical requirements of formats for entry
  • always comply with whatever the requirements are for type of file format and maximum size in terms of pixels and kilobytes
  • create a file which is the maximum allowed as this creates the best chance of creating an impressive image
  • if you can submit via a disc or via an upload to a formal submission website use an uncompressed file format (eg TIFF) if possible. This will create very large files of as good a quality as possible (but it won't make a bad photo look good - quite the reverse!)
  • if you have to submit online using email consider using jpeg - but appreciate that the quality of file may be less good than those submitted by others
Other tips:
  • find out how jurors will review the images. If they are reviewing via a slideshow or on a monitor screen then they certainly don't need to be 300 dpi (the standard for good quality prints)
  • always make sure you know how to create a new format/upload to a submission before you run out of time!
Images for fine art colour printing (eg giclee printing)
what you want: the very best quality image with the potential to print to the largest size possible
  • File format assumes you want the very best result possible - which means no compression or loss of pixels
  • unless you have an A3 scanner of good quality, large work needs to be photographed to a professional standard and you need to save the digital photos in the correct image file format
  • Use an uncompressed file format (eg TIFF - which can be created from jpeg files). This will: enable you to produce files with high quality images and create exceptionally large files
  • enable you to achieve the maximum possible size of image for the given image
TIP: if you ever want to check out what the file format of your image actually looks like then use the 'view actual size' option in the 'view' option. This shows you thse size and quality of the image you've created.

If any of you have any useful tips about which file format to use for different artistic purposes please leave a comment below.
Tomorrow [Update - sorry! On Friday] I'll cover the basic file formats and their characteristics.

5 comments:

A rambling rose said...

thanks Katherine for such a useful and clear overview - I too need to be reminded as it's so easy to be overwhelmed by image technicalities !!

Zsu said...

I partially disagree.

You do not mention the PNG format at all, which I consider one of the most important modern image formats. I suggest you read the wikipedia article on it, it has comparisons with all the image formats mentioned.

A clarification: TIFF files are not necessarily uncompressed - the format is not about compression, but storing the data. These files can contain uncompressed, lossless and lossy compressed data. Uncompressed data should not be used in general - if you want the perfect quality, use lossless compression.
But TIFF has many weak points in compatibility, so unless you need a specific TIFF-only feature (which you probably don't), I would recommend against it.

So I would modify the recommendation like this: graphics for web - PNG (GIF only for animations), pictures for web - JPEG, pictures for backup and competitions - PNG, pictures for print - PNG, rarely (LZW) TIFF.

Katherine Tyrrell said...

One of the points of creating these posts is so that people can share their views as we all have different perspectives on what's best to use.

Do please feel free to disagree with my views.

Explanations - as above are most welcome

Tina Mammoser said...

Gif is primarily for line/vector art. For the colour palette reasons you said, but worth pointing out it's particularly good case. :)

PNG is also suitable when a jpg is, and can sometimes be smaller in size. It also supports transparency if you need that (for example my blog header - the text - is a transparent png so the water image can be seen behind it)

And finally, much to my surprise, many professional printers now ask for high quality 300dpi (or higher) JPGs and not TIFs anymore. I work with a magazine publisher and the promotional company always wants jpgs for leaflets, flyers and posters (not tifs or pdfs). This is contrary to my years in the print world but a sign that things do change.

If you are using jpgs for professional printing the trick is to not resave over and over. Every time a jpg is resaved that new file re-compresses and loses some information. Work from one master file and always save fresh from that, not from later versions.

Katherine Tyrrell said...

Another supporter for the png - I need to do some more homework, I'm obviously not using this as much as I should!

I've come across that comment about jpegs before - but interesting to see you reiterating it and indicating it's becoming more usual.

I'm guessing this has much to do with the amount of files which wing their way around the internet. You wouldn't choose to email TIFFs too often!

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