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-   -   Cropping without affecting quality? (http://www.pixalo.com/community/general-photography-questions-answers/cropping-without-affecting-quality-21130.html)

Helena 18-01-2008 20:05

Cropping without affecting quality?
 
Hi
I have a photograph that I want to crop part out of. Every time I try though it reduces the quality of the photograph. Is there a way to crop a photo without reducing the quality?

Even resaving the same file without changing anything seems to reduce the quality. I use Paint Shop Pro and I've checked the compression is set to minimum.

Anyone offer any advice?
Thanks

Rob Barron 18-01-2008 22:00

Re: Cropping without affecting quality?
 
Hi Helena, a lot depends on what size your picture is before you start cropping and what resolution it is. Obviously you can't expect to crop a 72dpi shot very much and make the resulting one as large as the original as there just aren't enough pixels to do it properly.

The thing you should NOT do is to crop and enlarge in one movement. So don't have the sizes of the width and height set when you do the cropping as this forces the software to interpolate upwards in a big jump. First crop, then enlarge the remaining picture.

One tip I picked up a few years ago now and have stuck by ever since is this:

If you want to upsize a picture, do it in small increments. So rather than trying to increase a picture by 50% in one go, increase it by 10% five times. The result is invariably a much better quality that way.

There are software progs that do an amazing job of enlarging pictures really well with low quality loss but generally they're quite expensive.

One last thing, it could be nothing more than you are cropping and then viewing the picture at the same size as the original on your computer monitor and so it is looking lower quality. Have you tried actually printing out the result to compare it with the original? You may well find it hasn't lost the quality that you think it has. But you do need to be working with a printing resolution, ie between 240 and 300 dpi.

Cheers,
Rob :)

JMitchell 18-01-2008 22:26

Re: Cropping without affecting quality?
 
rob's answer is good, however in answer to your comment about losing quality when resaving, that is unfortunately an inherent defect of the jpg file format. This is why many people immediately save their jpgs as .tiff files which do not suffer (well, not really) from saving compresion. :thumb:

Les Meehan 18-01-2008 23:44

Re: Cropping without affecting quality?
 
Quote:

Originally Posted by JMitchell (Post 179287)
rob's answer is good, however in answer to your comment about losing quality when resaving, that is unfortunately an inherent defect of the jpg file format. This is why many people immediately save their jpgs as .tiff files which do not suffer (well, not really) from saving compresion. :thumb:

I picked up the same thought as Jack from your post. JPEG is one of the 'lossy' file formats, it discards pixel data as it compresses, and so you should never resave a jpeg image if you want to retain quality since it applies the compression each time you save the file. TIFF is one of the 'lossless' formats and can be saved multiple times without loss of quality as it does not discard pixel info.

So Jack's advice about saving a jpeg as a tiff is sound practice. Better still set your camera to save as tiff files if possible.

snap2photo 19-01-2008 00:14

Re: Cropping without affecting quality?
 
I'm not sure that the "jpeg is rubbish" is the whole answer here.

Are you loosing the quality in the print? There is sometimes "stuff" in the JPEG file to help with printing that is lost if you edit and save. (or just open and resave).

I think the lower end Fuji does not have colour managment stuff, but the higher end ones may have. Sometimes this is lost in the resave proccess. If you have the controls on the camera try using sRGB, not adobe colour model.

Is the "quality" the contrast, colour, sharpness or artifacts?

silkstone 19-01-2008 00:18

Re: Cropping without affecting quality?
 
As so often, I'll swim against the tide here. :D

Quote:

Originally Posted by Helena
Even resaving the same file without changing anything seems to reduce the quality. I use Paint Shop Pro and I've checked the compression is set to minimum.

Are you sure? PSP works the opposite way round from many editors, so the lower the value the higher the quality.

Choose Save As and then click on Options. Set the value to 5.

The theory goes that every time you resave a JPG it is compressed a little more and therefore degraded. But this does depend on a lot of things...

Some while ago I did a little test in PSP. I opened a JPG, resaved (with the quality set to 5), and then closed the file. Then I reopened the file again, resaved, closed..... 10 times.

The finished product was, perhaps, marginally degraded from the original, but nothing like as much as I had expected. My flabber was, in fact, totally gasted.

JPEGs are much maligned IMHO. It depends on the image and the software's JPEG algorithm, but you should be able to get really good results if you don't resave too often.

I suppose I'm going to have to repeat this now just to show that I'm not talking a load of dingos' kidneys. :Ponders: I won't do it right now - maybe over the weekend.

I hope I get the same results. :suspect1:

j sotelo 19-01-2008 02:55

Re: Cropping without affecting quality?
 
I remember there was a similar thread a while back some of the info might help.
http://www.pixalo.com/community/gene...age-18535.html
it was about upsizing, but again, some info might help.

Willow5075 19-01-2008 05:09

Re: Cropping without affecting quality?
 
So I just had a trial run at your suggestion Silkstone. Are you suggesting that 5 is good as a default setting.

Mine default (not having touched it since I started using PSP about 3 or 4 weeks ago) was around 25.

Markulous 19-01-2008 05:46

Re: Cropping without affecting quality?
 
Depending on the image, saving and resaving a JPEG will degrade the image - one of the reasons I moved from my Fuji S602 to dSLR was the in-camera interpolation which could go soft in some areas (and saving/re-saving definitely made it worse!)

BTW, the DPI setting on an image is totally irrelevant at the edit/save stage - used for printing only

Helena 19-01-2008 08:20

Re: Cropping without affecting quality?
 
Thank you everyone for all your replies! Part of the reason I am asking is that I want to enter this photo in a competition which means it will get printed out very large - possibly around A2 size. Had I known I'd have a fab photo I'd want to enter I'd have made sure my camera was set to its maximum 6M setting...but I didn't...but I've ended up with a photo I love and want to enter. The jpg file is big enough even after a crop to display that big so I think it will be okay, but I just wanted to see if there was anything I could do to make extra sure I didn't loose the quality at that size.

Unfortunately the competition only accepts jpg format, but I'll bear in mind the other formats for others things. :)

silkstone 19-01-2008 13:03

Re: Cropping without affecting quality?
 
Quote:

Originally Posted by Willow5075 (Post 179315)
So I just had a trial run at your suggestion Silkstone. Are you suggesting that 5 is good as a default setting.

Mine default (not having touched it since I started using PSP about 3 or 4 weeks ago) was around 25.

Yes, I find that 5 is a good default. 25 is far too high - anything over 15 can produce noticeable artifacts.

Dave Canon 19-01-2008 22:21

Re: Cropping without affecting quality?
 
Silkstone, your test will not really reveal the problem with resaving JPEGs. If you open then save the same unedited image any deterioration will be minor. However, if you edit the picture (even minor editing) then the input to the JPEG algorithm is different and a different set of approximations takes place. You only need to do this about 6 - 8 times to seriously damage the image. See the two examples below of a JPEG image before and the same image saved 8 times with very minor editing. You may not be able to see the editing but you can see the artifacts on the instrument and music.

Before

http://www.pixalo.com/gallery/data/978/Berfore1.jpg

After

http://www.pixalo.com/gallery/data/978/After1.jpg

Willow5075 20-01-2008 00:03

Re: Cropping without affecting quality?
 
Quote:

Originally Posted by silkstone (Post 179367)
Yes, I find that 5 is a good default. 25 is far too high - anything over 15 can produce noticeable artifacts.

Thanks fpr that tip I'll keep mine at 5 now that I know.

silkstone 20-01-2008 01:09

Re: Cropping without affecting quality?
 
Quote:

Originally Posted by Dave Canon (Post 179460)
Silkstone, your test will not really reveal the problem with resaving JPEGs. If you open then save the same unedited image any deterioration will be minor. However, if you edit the picture (even minor editing) then the input to the JPEG algorithm is different and a different set of approximations takes place. You only need to do this about 6 - 8 times to seriously damage the image....

Very good point, Dave. But it does depend on the compression settings and also the algorithm that the software uses. At the risk of going slight OT, I'm happy to do a RAW conversion straight to (low compression) JPEG, using Bibble + plugins which does not require second-stage editing for most pics, and go back to the original later for any tweaks. I'm happy to work on the JPEG for resizing etc, provided I don't resave more than once. What I try to avoid like the plague is a load of TIFFs - especially 16 bit - that just chew up disk space. :)

P.S. The ideal solution would be PNG which is compressed but lossless, except that it loses the EXIF data. :banghead:


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