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Rules for reducing graphic dimensions without pixelation
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spinningjennie
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Rules for reducing graphic dimensions without pixelation - 11/11/2004 7:01:32
Problem Summary:
What are the rules for successfully reducing the dimensions of a graphic, so that I don't get pixelation?
Problem Background:
I'm a graphics beginner.
I had an 180 dpi jpg image that I needed to fit to a page of an intranet site.
I used Photo Editor to reduce the size to 13% of the original size.
It was very pixelated.
I also have the use of PhotoShop (in case that helps).
Many thanks for considering my question.
spinningjennie
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Peppergal
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RE: Rules for reducing graphic dimensions without pixel... - 11/11/2004 9:14:54
Part of the problem is working with a jpeg - it is not a "resize friendly" format. The more you mess with jpegs the more distorted they become.
HOWEVER, Photoshop probably has something similar to what Paintshop Pro has called resampling. In PSP, when I resize an image, I have several choices of resampling methods. Each method produces different results. Bicubic is best for enlarging; bilinear is best for making smaller; sometimes smartsize is better...
l'm sure someone with Photoshop experience will be able to help you.
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_gail
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RE: Rules for reducing graphic dimensions without pixel... - 11/11/2004 13:48:24
quote:
f you want to crop the picture use image/canvas size.
I'd probably use the crop tool, so I can control where an image is cropped. You can set the exact dimensions you want, as well as the resolution, in Photoshop.
gail
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spinningjennie
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RE: Rules for reducing graphic dimensions without pixel... - 11/13/2004 21:18:55
Many thanks Peppergal, Donkey & Gail!!
1. The best resampling option for reducing size being bilinear is a great revelation!
2. Also the need to sharpen a reduced size image.
Gail - thanks for the useful urls. Yes I was surprised with the pixelation on size reduction also, but perhaps the following caused my problems:
1. I did reduce the size of a jpg rather than a PhotoShop file type. Perhaps jpg is more tricky.
2. Perhaps the Photo Editor program is too basic to resize with any sophistication, esp given my size reduction was to 13% original size.
3. Perhaps what seemed like pixelation was actually distortion of the jpg image.
Much appreciated!
spinningjennie
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d a v e
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RE: Rules for reducing graphic dimensions without pixel... - 11/14/2004 3:55:15
if you're reducing to something like 13% of the original size then reduce to 25% first apply a small amount of unsharp mask then reduce to the final size and apply a further amount of unsharp mask.
starting with a jpeg is not the best way but if that is all you have.. :)
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RE: Rules for reducing graphic dimensions without pixel... - 11/14/2004 4:58:29
but it's no better than the orginal lossy jpeg... obvisously you would save the jpeg in lossless format first (native programme format such as psd/fireworks png, or tiff, bitmap) buteven if you worked just with the jpeg i don't see how it can be any better or worse.
imagine you have a jpeg with noticeable artefacts - saving it as a tiff etc first isn't going to make it any better - it will be exactly the same.
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David Prescott
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RE: Rules for reducing graphic dimensions without pixel... - 11/14/2004 8:14:43
as far as i understand it - and i'm not 100% (maybe around 60%!) - whenyou open up a jpeg in say photoshop it parses the file decompressing it and displaying it as a bitmap. it doesn't work with it as a jpeg while it's open, obviously if you save it then (not save as) it will degrade in quality
try it with this pic
http://members.surfeu.fi/dave_pirjo/test-area/test_152k_2-15mb.jpg
it's 152k as a jpeg but when you open it photoshop it gives the document size as 2.17MB (the same as the doc size when you paste it in as a bitmap screenshot)
when PS is working with the jpeg it is a bitmap. probably. pretty sure ;)
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RE: Rules for reducing graphic dimensions without pixel... - 11/14/2004 9:17:07
oh don't misundertsand me: I agree of course you should save an original to work on (not just a jpeg, but as a tiff, or the applications native file format:psd, psp...).
If i had original artwork (picture, logo etc) in both rgb and cmyk i would save copies of both (print folder and a webfolder if needs be) as the gamut of colours is different between cmyk and rgb (process cmyk being usually less saturated and not containing some of the colours in the rgb gamut) still not a big problem as cmyk > rgb conversions are ok
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_gail
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RE: Rules for reducing graphic dimensions without pixel... - 11/14/2004 10:10:37
quote:
ORIGINAL: spinningjennie
1. The best resampling option for reducing size being bilinear is a great revelation!
Give it a try. I always use bicubic, Photoshop's default. 90% of my work is with jpegs...and I take 100's of photos per week.
quote:
2. Also the need to sharpen a reduced size image.
Yes, you do need to sharpen reduced images, but do so sparingly. Since you have access to photoshop, use the Unsharp Mask filter as it gives you more control and you can see how the image is sharpening as you apply it. Always view your image at 100% when sharpening.
Here's a very basic tutorial about sharpening:
http://www.digicamhelp.com/learn/image-editing/image-sharpening.htm
quote:
1. I did reduce the size of a jpg rather than a PhotoShop file type. Perhaps jpg is more tricky.
Personally, I don't find working with jpgs any more or less difficult than working with most other file formats. I'm sure you know this, but always preserve your originals. Edit copies of originals so if you goof, you can start over again by working on another copy.
quote:
2. Perhaps the Photo Editor program is too basic to resize with any sophistication, esp given my size reduction was to 13% original size.
I'm unfamiliar with the program you mention but if you're reducing an image 13% you should probably use a more sophisiticated one like Photoshop.
It is possible to reduce an image as small as you say, and still have it look decent to the human eye. If you look at the header graphic in the example below, all the thumbnail images were reduced from original images taken with a 5 megapixel digital camera. The originals were pretty huge.
http://www.digicamhelp.com/about/jarrell-conley.htm
Yes, I reduced the size of the images and sharpened each in increments.
quote:
3. Perhaps what seemed like pixelation was actually distortion of the jpg image.
If you didn't select "constrain" when you reduced the image, it would become distorted.
I realize you said you were a beginner and that some of what has been said may be over your head. So just take the basic steps and you should be successful in reducing jpegs.
I'd be happy to take a look at one of your images if you'd like and give some additional suggestions. Either post here or email one to me.
gail
< Message edited by _gail -- 11/14/2004 10:17:05 >
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_gail
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RE: Rules for reducing graphic dimensions without pixel... - 11/14/2004 16:07:05
quote:
So did you reduce them just the once and do you sharpen before reduction or after?
Once before reduction, then again after resizing. Usually a total of two times, sometimes three.
gail
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d a v e
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RE: Rules for reducing graphic dimensions without pixel... - 11/14/2004 16:16:57
gail do you do it *before* even if the photo is sharp? i find that a bit strange, so wondered what you get from it and whether i should start doing it ;)
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_gail
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RE: Rules for reducing graphic dimensions without pixel... - 11/14/2004 17:00:10
quote:
ORIGINAL: d a v e
gail do you do it *before* even if the photo is sharp? i find that a bit strange, so wondered what you get from it and whether i should start doing it ;)
Dave,
Good question!
Most advanced digital cameras, such as the one I own, produce "soft" images. The originals are not tack-sharp - by choice - out of the camera.
Manufacturers know that serious amateur photographers like myself prefer to have as much control as possible when post-processing (editing) an image. That's why many people who move from a point-and-shoot digicam to an advanced one initially complain about "out of focus" images. They are typically "soft" not out of focus.
Most point-and-shoot cameras have more aggressive, built-in sharpening algorithms which can not be changed. Advanced digital cameras have menu options so the user can select in-camera sharpening to high, normal, low, off. I keep sharpening to off.
So, to answer your question, if your original jpeg is very sharp, I probably would not apply an unsharp mask before reducing for the first time.
gail
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d a v e
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RE: Rules for reducing graphic dimensions without pixel... - 11/15/2004 0:01:17
ah i see - thanks for the explanation. :)
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Nigel
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RE: Rules for reducing graphic dimensions without pixel... - 11/15/2004 9:04:36
Here's a few extra points.
An image that starts off from only 180 pixels is unlikely to contain a lot of detailed information so there is a limit to what you can do with it. If you start of with a higher resolution image the final, smaller, resized image is likely to be clearer and sharper.
The debate over saving a jpg in non-lossy native format (tif, bmp, psd, psp etc) may be a result of a post I made here a few months ago. There are several reasons for doing this, the 2 major ones being:
Multiple compressions cause artifacts in the image (maybe what you're referring to as pixellation). Most image editors will ask you to set a compressioin setting when you try to save a jpg and every time the image is being compressed. Making all your adjustments in non lossy mode stops this. Only save as a jpg at the end when the image is ready to go on your site. It doen't matter if the image editor works on a jpg in bmp mode - each time you save as a jpg the image degrades. If you only do it once then its not too bad but if you work on an image save as a .jpg then realize it needs another tweak you have effectively 3 compressions on the one image (the original and the 2 you just made)
The 2nd reason relates to file size. You can test this if you want. Take a .jpg image image from your digital camera ideally a 2-3 million pixel image shot under the cameras lowest compression setting (i.e. the minimum compression - often the 'fine' setting). Make your adjustments in jpg format, resize and save as a jpg. Then take the same image, save in non lossy format, make your adjustments and save as a jpg (save for web in phtoshop). Compare the quality and file size.
You can also test this if you have an editor that allows resizing without recompression like irfanview (free). Resize the image without any alterations in irfanview then try the method suggested above, converting to non lossy first. Compare the file sizes.
Nigel
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_gail
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RE: Rules for reducing graphic dimensions without pixel... - 11/15/2004 9:32:48
Here's more to consider, from Popular Photography and Imaging magazine:
MYTH
When retouching and storing images, avoid resaving them as JPEG files, since each save to JPEG degrades the image and causes compression artifacts. Save them as uncompressed TIFF files.
FACT
This depends on your software. Before the release of Adobe Photoshop versions 6 and 7, resaving an image multiple times in JPEG format during the retouching process did indeed degrade image quality. And there are definitely a number of imaging programs out there that will do the same. But tests I've done using Photoshop 6 and 7 show no discernible degradation after retouching and saving an image 20 times as a JPEG file. (I originally saved the image at JPEG compression level 8 [high quality] in Photoshop and kept that setting throughout.) Only when I changed the JPEG compression to lower levels did I see image degradation, but most of this would have occurred after one save. Sure, you can eliminate any chance of additional compression artifacts by saving your digital scans and camera images as uncompressed TIFF files, but these require more storage space and take longer to copy, transmit, and open.
Source: 7 Lies & Myths
http://www.popphoto.com/article.asp?section_id=4&article_id=654&page_number=3&preview=
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d a v e
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RE: Rules for reducing graphic dimensions without pixel... - 11/15/2004 10:03:35
i don't think you can call it a myth when it's obvious that there will be some degradation - purely because jpeg compression throws away some information (lossy). now whether that is visible is open to debate and compression level and according to your tests isn't visible, but normal practice would probably require a little more agressive compression than high quality.
also i would imagine that image quality would suffer more (visibly) if the image was further manipulated - say resizing, altering levels etc - compared to working from the original file saved in lossless format.
I think the file considerations aren't significant when saving in rgb in the native file format (e.g. .psd) unless your working with hundreds or thousands of files and the time taken to open a reasonable sized image (say 1024x768) is minimal. large originals can always be backeed up to cd anyway.
While i think that your way may be a viable alternative it isn't one i would feel comfortable with - at least for my workflow of only teens-hundreds of images - and i think it's wrong to label it as a myth.
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_gail
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RE: Rules for reducing graphic dimensions without pixel... - 11/15/2004 10:24:11
quote:
now whether that is visible is open to debate and compression level
This is the key. It depends a lot on how you use the images and, for this discussion, the original poster was talking about posting on a website.
I only work with jpegs and have never had a problem, printed or for display on the web. For printed images over 8x10" there may be a visable difference.
quote:
also i would imagine that image quality would suffer more (visibly) if the image was further manipulated - say resizing, altering levels etc - compared to working from the original file saved in lossless format.
This, too, depends on your workflow. I use several layers and adjustment layers when post-processing. JPEGs work for me!
quote:
i think it's wrong to label it as a myth.
You're probably right, however I DO have great respect for Popular Photography magazine. And I think the advice makes a lot of sense particularly for "a graphics beginner." I frequent several photography and image editing forums. Some of the nitpicking can drive you nuts.
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RE: Rules for reducing graphic dimensions without pixel... - 11/15/2004 11:17:52
that's strange i was thinking it makes *less* sense for a beginner who might be prone to optimising quite harshly, go back and make changes to the last version of the jpeg and then save again, thus causing artefacts.
well the choice is there, but i think my opinion/advice would be to work from lossless originals, unless you know what you're doing and then feel free to take the jpeg route ;)
i won't nitpick anymore :)
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_gail
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RE: Rules for reducing graphic dimensions without pixel... - 11/15/2004 11:47:22
quote:
i won't nitpick anymore :)
lol, I don't think you're nit-picking at all (visit an inkjet printer forum if you want to see some good nit-picking). I only know that there is more than one way to approach things, including image editing and post-processing.
Sure there are beginners who are prone to optimizing harshly but they also can mess up no matter the process or file format they use. There is always a next-step in the learning process whatever our skill-level. That's what makes forums like this one so useful.
As an aside, from what I understand, if an original image is an 180 dpi jpg, saving it as a TIFF, for example, won't improve image quality.
gail
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Nigel
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RE: Rules for reducing graphic dimensions without pixel... - 11/15/2004 12:30:59
I can't agree that it's a myth but the method the author is using i.e. saving at level 8, is hardly any compression at all so the degradation be much less noticeable than saving at say level 5. It's not hugely different than working a lossless original. Ultimately it will have an effect.
Anyone tried the file size comparison yet? That is important for web images and is a good enough reason on it's own regardless of the views on image quality.
Nigel
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RE: Rules for reducing graphic dimensions without pixel... - 11/15/2004 12:36:19
Gail,
You're right about the saving in a different format not improving the image quality. You can only work with what you start out with, though Photoshop and paintshop pro can make a huge difference to a poor original.
A .jpg saved as anything else will still be exactly the same image regardless of the format it is saved in. From what I've read here I feel I may be stating the obvious to you as it appears you are well up on your graphics so apologies if thats the case. It will hopefully be useful for others.
Nigel
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