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Reflect
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Compressing graphics - 3/12/2004 12:16:28
Hello,
When you compress a graphic image or optimize it for the web what factors do you look at? This is for digital camera images being jpegs as the final output.
Thank you,
Brian
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Minix
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RE: Compressing graphics - 3/12/2004 12:48:03
As Mike says it's a quality versus quantity trade-off.
Generally with digital camera images, I find it necessary to first get the large image in its best rendition. That usually means cropping to get the proper image framing perspective, ridding the pix of noisy background and maybe doing some color touch ups.
Then I put a premium on load time, reducing the photo to its best size and use on the particular page. If it's a photo gallery of various partying customers at a bar, then I need to fit 12-14 pix on a page and I sacrifice a bit quality on each photo to help with the load time.
If it's one interior shot of the bar , to show it off, I probably give it a little more quality to show the place in its best light.
Go to netmechanic.com and use their free optimizer sometime and see how much difference you'll see in 60, 70, 80, 90 etc....compressions and load times of the same pic. To the untrained eye or causul web visitor it's not really noticeable in some renditions.
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d a v e
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RE: Compressing graphics - 3/12/2004 14:06:54
a *small* amount of gaussian blur or smoothing will generally help reduce a bit more filesize for a given compression ratio. also you can look at selective jpegs (fireworks, PS-image ready, others??) where you can use a lower quality in the same picture e.g. on the background , then use a higher quality on the foreground,/picture subject. basically it's trial and error,
judicious cropping not only imroves the picture composition helps by reducing the physical -and therefore file - size of the image.
some software, ovbiously, is better than others, helping shave off a few extra k.
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David Prescott
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JointComms
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RE: Compressing graphics - 3/13/2004 8:30:24
As said above quality is the major concern. In my case I never compress to less than 75%. If you're showing full-size images on a photo website perhaps people will expect the long time for the d'load of the image.
If it's just for monitor viewing bring down the res to 72 ppi and compress to 75% - use a batch conversion should you need to.
One other thing to take into consideration is the bandwidth - are you paying for it. Each time an image is downloaded FROM the server it is using your quota.
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_gail
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RE: Compressing graphics - 3/13/2004 9:35:52
quote:
ORIGINAL: Reflect
When you compress a graphic image or optimize it for the web what factors do you look at?
I think visual quality is the most important! But I also put a premium on load time so you need to find a balance. I have no rule as to how much compression to apply. My decision is based solely on how the image looks in Photoshop's Save For The Web menu windows.
The way digital cameras are made today, some sharpening is applied in-camera to images. Some cameras, such as the one I have, let you adjust the level of sharpening. In my case, I shut sharpening off so I can have full control.
Whatever the case, almost every digital image needs post-processing, particularly sharpening. I usually edit in this order:
Crop, if needed
Reduce in size
Adjust brightness and contrast, or adjust levels
Apply slight blur, if needed
Unsharp Mask, sometimes selectively
Some photos look terrible when reduced in size. In those cases, I offer both a small and larger version, such as here:
http://www.digicamhelp.com/photos/fog.htm
This is particularly useful if you have several images on a page. btw, I individually sharpen thumbnails as I want them to look as nice as possible too.
Watch out for oversharpening, which can cause the "jaggies." Here's some info:
It doesn't always come out the way you'd like it. But realize most people glance quickly at images and don't look at them as critically as we do. Unless an image is really lousy, their eyes fill in the gaps. Take a look at the sites of some of the major photo companies, look closely at their images, and you'll see what I mean.
gail
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d a v e
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RE: Compressing graphics - 3/15/2004 8:38:49
re: blur:
filter > blur > gaussian blur
the benefits are that it further smooths the transitions between colours/over gradients and smooths sharp edges thus allowing easier compression by the jpeg algorithm, with less loss in image quality.
obviously works better on some pictures than others. i assume as well it makes the image less susceptible to compression artefacts (those 'blotchy' bits you get when you push too far or have areas of solid colour)
re: tiff -
up to you, always good to have the original image in a lossless format if you need to go back and make further edits, otherwise you could just keep a copy of the original camera jpegs
if you find yourself having to save off lots of tiffs before working then you could record an action to convert file to tiff and save, then use this action in a batch action on a folder of camera images (without needing to open them all manually) then you can open the tiff images for editing and saving off.
re: sharpen - ideally you should sharpen (that is use filter > sharpen > unsharp mask), but for web use you may decide to omit this at some stages of image manipulation (it's more important for print work), but it's still good practice.
still you can make your own mind up at the time of manipulation as to whether you need to do it at every stage, or how much. it's certainly better to to several stages with a small amount of unsharp mask (e.g. after rotating, resizing) than one big one at the end.
You might also find that if you have an image that is 10x bigger than the final required you can reduce it by 25% or 50, use unsharp mask then resize to exact size (assuming it's smaller) then apply a little bit more unsharp mask
at least for web work what you see is pretty much what you get (you don't have to hope it prints ok!)
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Reflect
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RE: Compressing graphics - 3/15/2004 13:48:11
Thanks D A V E. I love the explanations.
Thank you,
Brian
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_gail
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RE: Compressing graphics - 3/15/2004 14:08:16
quote:
ORIGINAL: Reflect
quote:
Gail: Apply slight blur, if needed
Minix: a *small* amount of gaussian blur or smoothing will generally help reduce a bit more filesize for a given compression ratio
This is new to me. Can you elaborate on what the benefits are so I may understand the reasoning and also how you go about it (I use Photoshop CS)?
I think just about everything has been covered by David so I'll add a few minor points. I used Photoshop7 and no doubt the features are still in CS.
When you unsharp mask a photo, or apply most filters in fact, you can fade the intensity Edit > Fade. I find using the slider very helpful.
I'm personally going deeper into PS than I ever have before and the more I learn the more I realize I've barely scratched the surface.
I've started using adjustment layers so the original stays in tact. Layer > New Adjustment Layer. I'll also sometimes make a duplicate layer of the original (background layer) and apply unsharp mask to that...then I change the opacity of the duplicate. In some cases you can erase parts of the duplicate to, say, leave certain parts unsharpened (the duplicate layer of course must be on top of the bg layer).
I've recently discovered some fabulous information written by a Finnish photograher about a some of the key PS editing techniques. What I like about his writing style is that he takes complex things an makes them easy to understand. I've read so many complex things about using the Histogram that made me just about want to cry. I finally "got it" after reading this fellows work:
http://www.seittipaja.fi/data/Photography_lessons/Processing/a_Post-processing.html
Here's his excellent tutorial on Sharpening
http://www.seittipaja.fi/data/Photography_lessons/Processing/Lesson_2/_Sharpening.html
gail
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d a v e
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RE: Compressing graphics - 3/15/2004 14:53:01
that's a really excellent page - I thik had a fair grasp of what he's explaining, but now it's fuller and more concrete, so clearly explained!
his portfolio is really good, must be nice to live in finland, oh i do!
thanks again for that resource!
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David Prescott
Gekko web design
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d a v e
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RE: Compressing graphics - 3/15/2004 15:59:58
not been so cold so often this year, and it's nice when it's dry and crispy and there's loads of snow! but yes i miss the English rain, and to think as well that there's daffodils and we still have half a metre or more of snow in places
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David Prescott
Gekko web design
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Printable Version 
Also taken into consideration is the actual size (dimensionally) of the resulting image. If I want to present the image at 700 x 525 and keep the the file size down I'll have to compress it more than if I were to present it at 640 x 480, which all goes back to the compromises.
. 
Been to Finland many times. My husband's family live in Finland and Sweden. 