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Picture format question.......


Tony
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What is the difference between the likes of jpg, jpn, png?.... As images they all look the same?

That depends upon how carefully you look and at what image size. Some of them were designed for specific purposes; png for example and will not normally be used by photographers.

 

It's a huge question Tony and not one to which you can possibly get a comprehensive answer in a single reply to a website question.

 

There are answers available if you google and you might want to start with something like http://www.scantips.com/basics09.html which gives a general view of some of the most common image file formats and may well give the sort of generalised answer that I suspect you are looking for.

If you really want to understand where the various standards come from and what they try to achieve, then I think you need to look up each standard in somewhere like Wikipedia. I know there is a good write up of the jpeg standard there, but I can't really speak for the others.

 

Personally I use only three standards:- RAW, which is the data as it is produced by the camera without any processing; you cannot see an image in Raw format, it has to be processed into some form of image file and saved as an image file. For that purpose I use TIF, which is a lossless format and ensures that none of the data processed is lost; I then convert to JPEG (which is brilliant at reducing the size of an image file, but is lossy and throws away data in a way which is unrecoverable) if I want to send it with an email or put it on a website.

 

All the image files that I want to keep I store in RAW & TIF formats i.e. all the original data is saved.

 

Every time you process and save a jpeg it loses data (and therefore quality). Even if you only rotate a picture from landscape to portrait format and then save it, if it's a jpeg you lose data and can never get it back.

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Seems odd day to day images are taken in high res. I know the forum refuses to upload the simplest of images because of the format which is annoying because i would have thought it would automatically change the file type?

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Seems odd day to day images are taken in high res. I know the forum refuses to upload the simplest of images because of the format which is annoying because i would have thought it would automatically change the file type?

 

High resolution, file type and size are all different things.

 

High res refers to an image being 300dpi, which is print quality, web quality is low res at 72dpi. DPI = Dots Per Inch, the number of pixels that makes up a square inch of an image. The lower the number the more the quality suffers but the filesize will also reduce, which is why it's ideal for websites, they load quicker.

 

I get so many photos sent to me at work that have been taken with a DSLR camera (so the image would usually be 300dpi) but then they resize/resave it and strip all the detail away, like sagitar said. However, as long as the photo as been taken at the highest dimension the camera allows and they don't change this, then saving it as a JPG is fine.

 

TIF is one of the better file formats but produces very large sizes and is not practical for emailing.

JPG compresses the image so it does lose some quality and photos can be saved in this for print and web use.

GIF is for web use only and not really suitable for photos but more graphics like logos.

PNG is supposed to be the replacement for GIF files. It's similar to JPG in terms of quality, although produces higher file sizes for photos, whereas graphics would be lower. However, with PNG you can also save a transparent background on a photo and keep the quality decent, which you can't do on a GIF.

 

This is a JPG.

 

DSCN2549.JPG

 

This is a PNG but I cut the sky out so the forum background shows instead.

 

DSCN2549.png

 

If I save it as a GIF the quality of the photo reduces. It won't be as noticeable as I've made the dimensions small but the big giveaway is the edges of the roof and satellite dish now look jagged and rough, on the PNG it's smooth. It's not the best example, I'll try and do another.

 

DSCN2549.gif

 

With the forum you are probably finding it's the file size that is the problem and not the format, it's limited to 2MB per image file. You can upload the following file formats to the forum - jpg/jpeg, gif, png and bmp. The forum can't change the file type, you need to use dedicated software to do that.

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