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Bmp or Jpeg.

 
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HillBilly



Joined: 10 Aug 2006
Posts: 21

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PostPosted: Tue Aug 15, 2006 9:06 am    Post subject: Bmp or Jpeg. Reply with quote

Jpeg or Bmp.

I was gonna post this as an answer to a forum question but thought it may be better to start a new thread. Please post any comments if I have over looked or indeed got something wrong, I am by no means an expert but I have a passion for all thing computer related and try to share this in my own way.

Well if you are working on a picture at home and will be doing lots of edits and saves before it is finished, then you should be using a lossless saving version in the Jpeg format if your software offers it, but a lot of software bundled with the camera is basic at best. I would recommend that while editing you save each time in Bmp format.
“why?” you shout. Well here is my example that I have done to explain why.
As mentioned above, most cheaper software does not offer you Jpeg compression options as we have already seen with the Avatar problems and the like, which also means that it will just compress to a built in level that you have no control over. It maybe lossless or it may compress to a degree that you do not notice but it has compressed and therefore has degraded your image.
Bmp works in this way, each pixel is allotted a piece of data, if you imagine a chess board, 64 squares each one has a colour. Bmp will save each square by looking at where it is and what colour it is, creating a larger file but an exact replica at the same time.
Jpeg will not do this and will squeeze you image into a smaller file size.
Which is great for sending to friends over the net or for posting to us lot on here, but ultimately, quality is lost for ease of use.

I have included a quick sample to show you what can happen with a compression factor of 20.
The second picture (now cropped) started out with,
121204 many colours, then with each save it increased...
134041
136684
138172
What this means is that there is some blending and softening going on, but did we ask it to soften the image that we spent £50 on a tripod so as to avoid shaking and to make crisper, NO WE BLOODY DID NOT Twisted Evil

The first image was edited in Bmp format then saved, for the benetit of posting up here, in Jpeg format. The black shape on picture 1 has a clear blur around it to highlight the loss of quality and the way a jpeg actually deals with your photos.
So to conclude, edit in Bmp and once you reach the point where you have finished all editing and are happy with the result, save to jpeg to be able to post to friends and forum buddies.
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Kit



Joined: 25 Sep 2005
Posts: 2547
Location: Nottingham

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PostPosted: Tue Aug 15, 2006 8:47 pm    Post subject: Reply with quote

I do much the same with my family photos, but use PNG as the low-loss format rather than BMP. Seems to work OK – you're right about JPG, though, it can be really horrible. I've been sent scans of photographic prints saved as JPGs at low resolution, and the people in them look as if they're wrapped in cling-film!
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Tricia



Joined: 08 Apr 2005
Posts: 3579
Location: Surrey

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PostPosted: Tue Aug 15, 2006 10:20 pm    Post subject: Reply with quote

I also save as PNG which also works for me. The final version for printing I then save as JPEG.
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Tricia
What is this life if full of care, We have no time to stand and stare?

http://belfiebird.blogspot.com/
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gasteropod



Joined: 23 Mar 2005
Posts: 151
Location: SU 66445 55387, Chineham, Basingstoke

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PostPosted: Fri Aug 18, 2006 4:49 pm    Post subject: Reply with quote

I don't believe that standard jpeg supports a lossless mode so even if you select a high quality setting every time you save an image the quality will always de-grade. Therefore if you are going to be editing files and saving several times you should not save as jpeg even if they started as jpeg.

Only the newer jpeg 2000 standard allows for lossless images. I would expect these to have a different extension like .jp2

The problem with bmp files is that they are not usually compressed so can result in some very large files if the picture is of a high resolution. The other problem is that this is really a windows only format so tends to have less support on other platforms.

The other alternative is to use a format which does compress the image so makes it smaller, but is not lossy so you do not loose any quality at all when loading and saving. The png format is one of these and is rapidly becoming the commonly used format over and above gif which had patent issues until the patent recently expired.

If you are more interested in the subject I would recommend Wikipedia which has a very good entry at http://en.wikipedia.org/wiki/Lossless including direct links to other entries for other formats.

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Kit



Joined: 25 Sep 2005
Posts: 2547
Location: Nottingham

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PostPosted: Fri Aug 18, 2006 6:28 pm    Post subject: Reply with quote

Thanks for that, G – I hadn't thought of looking at Wikipedia.

Someone recently asked me why I choose to use PNG instead of JPG to edit the large number of photos I've 'digitised' as part of a family history project, and I managed to explain that using JPG for images that are likely to be edited several times is a bit like photocopying a photocopy. They also asked something that I realised I was much less clear about; it might be of general interest, so I thought I'd ask if you knew.

I set the photos on black canvases, so I can put people's names on them – but sometimes, with wedding groups etc, I need to send a proof version back to to the owner, to check I've got all the names right. I always scan the originals at high resolution, but usually reduce these proof versions to about 300 dpi to make them easy to email. I tell people not to keep them even if they're correct, as the final version will be much better quality – on the assumption that, once reduced in size, the original quality can't be recovered no matter what format you use. My uncle was arguing that that's not the case, and I'm at the limit of my understanding of how these things work, so I decided not to dig my heels in!

I suspect that it's not an entirely straightforward issue, but in general, if a photo has been reduced in size by half or something, am I right in thinking that re-sizing it to the original dimensions would result in a poorer-quality image than the original?

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Tricia



Joined: 08 Apr 2005
Posts: 3579
Location: Surrey

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PostPosted: Fri Aug 18, 2006 6:35 pm    Post subject: Reply with quote

Kit wrote:

.......I suspect that it's not an entirely straightforward issue, but in general, if a photo has been reduced in size by half or something, am I right in thinking that re-sizing it to the original dimensions would result in a poorer-quality image than the original?


I've no technical knowledge for saying this, but I have always made the same assumption.

Your description of "lossy" being equivalent to photocopying a photocopy, is excellent and one I shall remember in my explanations. Just wish I'd thought of it. Applause Applause

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Tricia
What is this life if full of care, We have no time to stand and stare?

http://belfiebird.blogspot.com/
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HillBilly



Joined: 10 Aug 2006
Posts: 21

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PostPosted: Fri Aug 18, 2006 7:08 pm    Post subject: Reply with quote

Resizing a smaller image back to a larger one will cause a loss in quality as the software can only guess what the extra pixels colour would be.
If you are worried that maybe some of the photos you send out for proofing reasons may find themselves on the father-in-laws mantle piece Wink try stamping a great big SPECIMEN across the picture before you send them out.
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gasteropod



Joined: 23 Mar 2005
Posts: 151
Location: SU 66445 55387, Chineham, Basingstoke

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PostPosted: Fri Aug 18, 2006 7:54 pm    Post subject: Reply with quote

Kit wrote:
I set the photos on black canvases, so I can put people's names on them – but sometimes, with wedding groups etc, I need to send a proof version back to to the owner, to check I've got all the names right. I always scan the originals at high resolution, but usually reduce these proof versions to about 300 dpi to make them easy to email. I tell people not to keep them even if they're correct, as the final version will be much better quality – on the assumption that, once reduced in size, the original quality can't be recovered no matter what format you use. My uncle was arguing that that's not the case, and I'm at the limit of my understanding of how these things work, so I decided not to dig my heels in!

I suspect that it's not an entirely straightforward issue, but in general, if a photo has been reduced in size by half or something, am I right in thinking that re-sizing it to the original dimensions would result in a poorer-quality image than the original?


You should have dug your heels in.

If you reduce the dpi you are removing information from the image to make it smaller. There is no way to put that information back without the original. What normally happens depending on the quality of the photo package is that when you enlarge an image it interpolates and tries to estimate what information is missing and put it back. However, this will never match the original. If it did think of the space savings you could make by saving all of your images a 1 dpi and then enlarging them back to 10000 dpi for poster printing Smile

This pretty much applies to any operation other than lossless compression that reduces the file size. Information is removed in order to save space which cannot be replaced without a loss of quality compared to the original. This is always the compromise you must make, space versus quality.

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Kit



Joined: 25 Sep 2005
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PostPosted: Fri Aug 18, 2006 9:02 pm    Post subject: Reply with quote

Tee hee! Thanks, both, I thought so.

Trouble is, I easily get blinded by terminology – I make sense of concepts like this by finding concrete examples to compare them with (ie the photocopying a photocopy idea), and as soon as anyone starts talking proper computer-speak, I assume they know more than me! Very Happy

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Kit



Joined: 25 Sep 2005
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PostPosted: Fri Aug 18, 2006 9:22 pm    Post subject: Reply with quote

Tricia wrote:
Your description of "lossy" being equivalent to photocopying a photocopy, is excellent and one I shall remember in my explanations. Just wish I'd thought of it. Applause Applause


...but they aren't always entirely successful, Tricia!!

I was explaining a couple of years ago to a student that if he continued applying gloss paint to a door at quite the thickness he'd started at, it would (a) run and look horrible, and (b) take at least three weeks to dry. He wanted to do a good job, so he asked for some top tips on painting. I said that I found the best way to use gloss paint was to work as if you're not sure you've got enough left to finish the job. Thinking this would encourage him to apply it a bit more thinly, I left him to it – only to return half an hour later, to find that he'd solved the 'shortage' problem by diluting the paint with half a bottle of white spirit! I sometimes think women are better at this kind of visualisation than men...

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Tricia



Joined: 08 Apr 2005
Posts: 3579
Location: Surrey

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PostPosted: Fri Aug 18, 2006 10:27 pm    Post subject: Reply with quote

Kit wrote:
Tricia wrote:
Your description of "lossy" being equivalent to photocopying a photocopy, is excellent and one I shall remember in my explanations. Just wish I'd thought of it. Applause Applause


...but they aren't always entirely successful, Tricia!!

I was explaining a couple of years ago to a student that if he continued applying gloss paint to a door at quite the thickness he'd started at, it would (a) run and look horrible, and (b) take at least three weeks to dry. He wanted to do a good job, so he asked for some top tips on painting. I said that I found the best way to use gloss paint was to work as if you're not sure you've got enough left to finish the job. Thinking this would encourage him to apply it a bit more thinly, I left him to it – only to return half an hour later, to find that he'd solved the 'shortage' problem by diluting the paint with half a bottle of white spirit! I sometimes think women are better at this kind of visualisation than men...


Think that sums it up very well Kit Smile Rolling Eyes Rolling Eyes

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Tricia
What is this life if full of care, We have no time to stand and stare?

http://belfiebird.blogspot.com/
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Tricia



Joined: 08 Apr 2005
Posts: 3579
Location: Surrey

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PostPosted: Fri Aug 18, 2006 10:29 pm    Post subject: Reply with quote

Gasteropod - it's really very logical when you think about it.
Thank you for such a clear and precise explanation Applause Very Happy and thanks to you to HillBilly

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What is this life if full of care, We have no time to stand and stare?

http://belfiebird.blogspot.com/
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