Tools of the Trade: Image Formats

Hey man, it’s the digital age! So here’s some info all comic artists should know about bitmap image formats (and, if you’re a masochist, you can drill into the wikipedia entires I’ve sprinkled throughout):

Ok, let me define BITMAP – imagine a grid, within that grid each element (or pixel) contains a filled in colour. If your grid is big enough then the grid will look like a picture. And that’s a bitmap.

(Alternatively, there are VECTOR formats – VECTOR formats are like someone describing what a picture looks like – “in the centre is a red circle with a diameter of 300, then, 30mms to the left is a blue square that’s 15cm x 15cm” – the advantage of a vector format is that you can scale it – ie make it bigger – without decreasing the quality, the disadvantage is that, for MOST comic art, it’s pretty useless at describing artwork)

Now, BITMAP image formats are Designed to hold as much information in as little space as possible This is accomplished by using compression. There are two very basic types of compression: LOSSLESS and LOSSY.

LOSSLESS compression is designed to compress the data while keeping every single bit of information intact. This works brilliantly for some things (notably, b&w, cartoony type images, and comic book lettering – that is lettering that has been converted to artwork).

LOSSY compression is designed to compress data while throwing away information that the human eye doesn’t really process, so works brilliantly for natural colours, photos or paintings. The eye can see around 200 shades of green and only a handful of shades of red – and this style of compression makes use of that fact. An artifact of this, though, is that it looks terrible with images that it doesn’t compress well (b&w, cartoony, and comic book lettering) – these are the dreaded “Jaggies
So, now we’ve covered the basics, let’s get some image formats:

GIF – the GIF format is a LOSSLESS compression that works brilliantly for b&w. Some key factors:
1) It can hold up to 256 colours – that means, for fully painted work it’s absolutely rubbish – it looks poor and doesn’t compress well at all.
2) Because it’s lossless it really is brilliantly sharp for lettering and cartoony colours.
3) You can actually specify how many colours you want the gif format to hold, making a small file size EVEN smaller. Typical pure b&w comic art can often be reduced to four colours without any loss of fidelity and it can make a big difference on your file sizes.
4) It’s a common format on the internet and designed to handle relatively small images photoshop, for example, will not allow you to export a gif if the image is too physically large.

GIF is my favoured method of emailing people decent sized web preview images – large (ie around 1024pixels wide) can be surprisingly small if you reduce the number of colours to four or so.

JPG – JPG is a LOSSY format, that uses some clever maths to throw certain colours and details away from the image.
1) Ideal for photos – the JPG format can hold a massive amount of colours/information in a relatively small size by throwing away lots of stuff that you wouldn’t notice. You can also specify how much information it should discard.2) Editing a JPG and then resaving as a JPG will reduce the quality. In fact, if you keep opening and saving the same JPG eventually you’ll have nothing but a handful of weirdly coloured pixels3) JPGs have a problem going from one extreme colour to another – rapid transitions from black to white (as you’d find, for example, in lettering) the transition areas end up clogged full of ‘artifacts‘ – weird little quilted bits of colour in the picture.

JPG is a great way to deal with full painted art, and, with a low level of compression the artifacts on lettering aren’t too noticable. BUT it DOES NOT remain 100% true to the image as created – by virtue of being a lossy compression format.

PNG – designed to overcome many of the limitations of GIF – the PNG format is a LOSSLESS format that allows millions of colours and adds lots of cool features for people building websites, but for our discussion only a couple of things are relevant:
1) Can compress comics relatively well – allowing for lots of colours while keeping the true to the original artwork.
2) File sizes are usually bigger than GIF for smaller images
3) Only the past few years has it been widely supported – many windows based PCs running old version of software can’t really see PNGs properly.

PNGs a good format, but, as it’s so (relatively) new, unless you need it’s advantages it’s probably easier to stick to GIF or JPG for emailing or putting on a website.

TIFF – Lossless format designed for print.
1) Tiff files can be physically massive while being tiny in memory. Even an A3 pure B&W image can compress down to as little as 300kb.2) Pretty much the lingua franca of comic pros sending art for publishing.
3) Can also hold colour and layers – though, once you start doing that, files get big pretty damn quick.

TIFF – if you’re publishing your work, you’ll find yourself using TIFF – photoshop (for example) offers multiple ways to compress TIFF files, but, afaik, most people go for the standard LZW compression.

PSD Uncompressed file format, used by Photoshop.
1) Files are MASSIVE
2) It’s photoshop’s default format

Well, that’s it. If you use PHOTOSHOP you’ll use PSD. If you don’t – well, PSD files are so universal most publishers will have something that can read them, but you’re better off sticking to TIFF for this.

So, to sum up:

If you’re putting a b&w or cartoony comic on the web: use GIF (or PNG if you don’t mind internet explorer 5 users missing out) if you’re putting a fully painted/full colour comic on the web use JPG.

If you’re sending files to a publisher use TIFF.

Hope that helps, if you find anything in error, please feel free to let me know in the comments and I’ll update.

Author: PJ

Belfast based Comic Artist who won’t shut up on twitter.