Why JPG isn't all its cracked up to be

If you shoot and edit your pictures you will know that JPG is the perfect file format for sharing your images pretty much everywhere as they are decent quality and a small file size.

JPG or JPEG (Joint Photographic Experts Group) has been around since approximately 1986 but first became public in 1992 and has been the standard ever since because it just works and why change something that works right?

Well it is still a great format and is highly recommended as a final image format for sharing on the internet and even for getting prints done.

But the reason it is so useful can in some cases have a negative impact on your images and that reason is that it can be compressed down to a pretty small file size.

The reason for this is that JPG is a 'lossy format' What this means is when it uses its algorithms to compress the image it will remove parts of the image that are not needed or would not be seen in everyday use.

99% of the time nobody will notice as the image from its original format whether that is RAW, TIFF, DNG or any of the other lossless formats will look practically identical at least for everyday use and it would be fine if you have save it once or even a few times from its original format.

But, because it is a 'lossy' format, each time you save the file over itself it will get compressed a little bit more and the quality will degrade.

If you are saving at high quality it will take a LOT of re-saves before this is noticed but it is worth bearing in mind.

To show you what I mean I have created some examples.

I have taken an image that was originally taken in RAW and then after my edits was saved back as TIFF (Both lossless formats) and I have then exported it twice as a high quality JPG but resized to be a bit more manageable.

I have then taken one of those JPGs and edited it and re-saved it many many times but my edits have just been to put a bit of black in the already black background so it wont get noticed but will be enough for Photoshop to see that the image has changed and will let me overwrite the original image.

If you look at the images below you will see what happens each time an image

First of all here is the Original JPG, exported from my edited TIFF file. You can click on it to see a larger version

Next, the same image but resaved many, many times.

Hopefully you can notice the degradation especially around the neck area. If its not too obvious due to the way my website resizes the images here is a 100% crop

Here is an animation to show it better

As you can see the quality has decreased quite significantly although the way my website works it still doesn't show it quite as bad as seeing the full sized images.

Now this doesn't mean don't save in JPG because JPG has been around for a long time and is definitely the standard to use for webpages (as well as PNG and/or GIF) and when worked on properly it will look absolutely fine.

BUT if you find you are constantly going back to the image and making minor tweaks then follow one of these two steps:

1. Only ever edit the original RAW, TIFF etc lossless image then when you are happy with your edits then save it as high quality JPG and leave your RAW, TIFF etc as the original.

2. Keep your original JPG as a working copy and only save to a new JPG file rather than overwriting the previously edited JPG. Like I mentioned it takes a lot of saves before you will notice any difference but why take the risk. I hope this little blog is useful to you and I hope you continue to follow my blogs and website and if you do think it is useful please tell your friends to follow me too.

Thanks Darren

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