What are the advantages of Bitmap over JPEG images

  Nick.A 12:35 22 Jul 14
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What are the advantages, if any, of Bitmap images over JPEG images? Do bitmap images degrade slower than jpeg images? The reason why I ask is because I have saved a lot of bitmap images to a USB flash drive, but they are tacking up a lot of space on the stick. If there is no obvious difference then I’ll start saving images in jpeg format instead, to save on space.

  Secret-Squirrel 13:04 22 Jul 14

There's no loss of image quality with bitmap files - even when they're compressed.

The JPEG file format is perfect for photographs as most of the detail is retained and the file sizes are massively smaller than bitmaps. However, it's a "lossy" format which will lower the quality of the image a tad and introduce some unwanted artefacts. Having said that though, most folks will never notice so it's a perfect format for the average home user.

Professional photographers and graphic artists nearly always work with bitmap images.

  Batch 14:03 22 Jul 14

With bitmap, a bit (pixel) is a bit is a bit is bit.

The JPEG standard supports various degrees of compression and types of compression coding. Most of the time you won't be aware of the various different options - i.e. you just use a programs default JPEG file settings (when creating / converting to JPEG).

If I recall correctly, one of the key parts of JPEG compression is that it assesses each pixel and its adjacent pixels for difference in colour and brightness. The compression algorithms tend to have a bias for compressing colours (that are the same or nearly the same) over levels of brightness (as, supposedly, the human eye is more sensitive to slight variations in brightness rather than slight variations in colour.

The more severe the compression used, the more likely one is to be able to detect it. But most amateur photographers will be using JPEG as the default anyhow (as that is what their cameras do by default) and none the wiser.

  alanrwood 15:05 22 Jul 14

Also continually saving and re-saving a jpg results in more degradation each time so if playing about with a jpg always work on a copy file not the original then do everything on the original in one go and re3save it just the once under a second filename.

  imendpc 22:43 22 Jul 14

One alternative to reduce size drastically without loosing the bitmaps detail is to compress using winzip, 7zip or Winrar etc.. "alanrwood" to avoid more degradation to jpeg file, subsequent saves to jpeg adjust the compression level to 0.

  Nick.A 20:16 23 Jul 14

Okay, so from what you are all saying, I understand that Bitmaps don't degrade, but Jpegs do, but only if they are re-saved often, but they don't degrade if they are only opened for viewing from the USB stick frequently. Is that correct?

  Batch 07:54 25 Jul 14

I get the impression that you have the idea that somehow image file types degrade over time and some don't.

In principal, NONE of them degrade overtime (whether they are just sitting there on the device or being viewed once, twice or a million times).

However any files on any storage medium (e.g. hard disk, memory sticks, CDs, DVDs) are prone to damage or loss due to breakdown or failure of the storage medium itself. That's why it is vital to have backup copies. It is a good idea to keep at least two backup copies on different mediums and stored in different places (e.g. on an external hard disk and on a memory stick, with one of these stored "offsite" [e.g. at a friend's or relation's house]).

  alanrwood 10:45 25 Jul 14

Batch

Just to clarify. In principle you are correct but jpgs do deteriorate every time they are resaved as opposed to being copied between various disks. They do not degrade if they are just viewed which is what I posted above.

If you want to try this Nick copy a jpg from the original then open it in a graphics program ie Paint shop Pro, Photoshop etc. Edit one pixel somewhere and resave the file with a different name. Repeat that about 20 times and compare the original with the final one which will have become very blocky. This can happen if editing a jpg and saving it every time you make a slight change.

  john bunyan 19:05 25 Jul 14

I believe if you shoot in .RAW and process with Lightroom or Photoshop, you can save the final result as a .jpeg but the original .Raw file is unchanged. I agree with Alanwood.

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