Is 72ppi still standard for screen viewing, and optimize image size questions
RovingEyePhoto
Registered Users Posts: 314 Major grins
I process RAW to TIF through ACR (exposure, contrast curves, sharpening, toning, etc), and only then open in PS (CS3) for sizing and conversion to JPEG. I process a lot, and this workflow seems to do an adequate job while moving things along at a fast clip. When setting "Image size" in PS, I set resolution at 72ppi (for screen viewing, not printing), but seems to me I've read that with ever-improving screen tech, possibly a higher ppi setting would be more all-purpose. Or does PS default to 72ppi anyway when I "Save for web and devices ...", and if so can I set the default to something more currently all-purpose? Any thoughts on that?
I also have a question on the "Optimize menu" on the "Save for web and devices ..." pop-up, allowing me to specify JPEG k size desired, which I don't use. What I do use is "Image"/"Image size" on the main PS screen, setting resolution to 72ppi (as discussed above), and based on experience reduce inches of "Document size" to what I think will result in a 100%-quality near-570k JPEG with no upsampling. If the "Save for web and devices ..." pop up ultimately shows at least 96% "Quality" at near 570k (or if heavily cropped, some k less), I'm a happy camper. Sometimes, however, I guess wrong in reducing inches of "Document size" (or if heavily cropped, leaving as is), so have to cancel and close the "Save for web and devices ..." pop-up, click "Step back", and perform "Image size" all over again, an obvious time waster. Doesn't happen all that often, but still often enough to be a pill. So here's my question: if I use the "Optimize menu" on the "Save for web and devices ..." pop-up to set file size at 570k, will I avoid the guessing and mouse moves I presently perform in coordinating "Image size" on the PS screen and "Quality" on the "Save for web and devices ..." pop-up, while at the same time be able to keep minimum 96% quality with no upsampling, or are "quality" and upsampling the exact thihgs PS is fiddling with in delivering its consistent 570k file size, so I lose on those? As I write this, seems pretty obvious these in fact are what PS is fiddling with, so maybe I've answered my own question, and should continue with the present way I handle things. Thoughts?
Final question. When I hover over the "Optimized" check box on the "Save for web and devices ..." pop-up, I get a pop up that says "Creates smaller but less compatible files". If I check the box, which I think I inadvertently have done at times in the past, what compatibility am I losing? I haven't witnessed any problems in uploads to Flickr, SmugMug and other sites, or in email attachments, so maybe the incompatibility is so esoteric I don't have to worry about it, but curious nonetheless. In general, should I be checking this box or not? Thoughts?
Thanks for taking the time.
Stan
I also have a question on the "Optimize menu" on the "Save for web and devices ..." pop-up, allowing me to specify JPEG k size desired, which I don't use. What I do use is "Image"/"Image size" on the main PS screen, setting resolution to 72ppi (as discussed above), and based on experience reduce inches of "Document size" to what I think will result in a 100%-quality near-570k JPEG with no upsampling. If the "Save for web and devices ..." pop up ultimately shows at least 96% "Quality" at near 570k (or if heavily cropped, some k less), I'm a happy camper. Sometimes, however, I guess wrong in reducing inches of "Document size" (or if heavily cropped, leaving as is), so have to cancel and close the "Save for web and devices ..." pop-up, click "Step back", and perform "Image size" all over again, an obvious time waster. Doesn't happen all that often, but still often enough to be a pill. So here's my question: if I use the "Optimize menu" on the "Save for web and devices ..." pop-up to set file size at 570k, will I avoid the guessing and mouse moves I presently perform in coordinating "Image size" on the PS screen and "Quality" on the "Save for web and devices ..." pop-up, while at the same time be able to keep minimum 96% quality with no upsampling, or are "quality" and upsampling the exact thihgs PS is fiddling with in delivering its consistent 570k file size, so I lose on those? As I write this, seems pretty obvious these in fact are what PS is fiddling with, so maybe I've answered my own question, and should continue with the present way I handle things. Thoughts?
Final question. When I hover over the "Optimized" check box on the "Save for web and devices ..." pop-up, I get a pop up that says "Creates smaller but less compatible files". If I check the box, which I think I inadvertently have done at times in the past, what compatibility am I losing? I haven't witnessed any problems in uploads to Flickr, SmugMug and other sites, or in email attachments, so maybe the incompatibility is so esoteric I don't have to worry about it, but curious nonetheless. In general, should I be checking this box or not? Thoughts?
Thanks for taking the time.
Stan
See my work at http://www.flickr.com/photos/26525400@N04/sets/. Policy is to initially upload 10-20 images from each shoot, then a few from various of the in-process shoots each time I log on, until a shoot is completely uploaded.
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You can set your ppi to anything you want, and it will not affect your image in any way. A 800x600 pixel image at 600ppi is the EXACTLY the same a 800x600 pixel image at 72ppi. You set your image size in pixels for screen viewing, and that is it.
http://pennyphotography.smugmug.com/
Thanks for taking the time.
The optimum output resolution for jpgs is highly variable and directly dependent on what the jpg is to be used for. In general, unless there is is specific requirement to reduce the size of the file, save them at the original resolution, and the highest quality setting. It is a good policy to never discard data unless necessary.
But it all boils down to why you are making jpgs at all. Until you are very clear as to why you need the jpg in the first place, then optimizing it is a mute point.
I myself don't make many jpgs. A few here and there for emails. My Smug Mug jpgs are created on the fly by the SM uploader, so I don't have much need to mess with jpgs at all. Other posters have expressed similar observations.
Anyway, I hope this helps a little.
Lee
Thunder Rabbit GRFX
www.thunderrabbitgrfx.com
Addressing this part of your post only...I have never seen any report that says that greater than 72ppi is useful on any screen of any monitor of any make. I have seen a lot of people commenting - as you have - that there might be some reason to anticipate technical improvements and save in larger number than 72. All conjecture.
Until some reputable source comes out with a definitive statement that there is a reason to use a larger number than 72, I'll stick with that.
http://tonycooper.smugmug.com/
Mmm… …well, I thought I understood this but obviously I don't. Would you care to elaborate further in order to make it clear to an ignoramus such as me?
Many thanks in advance!
- Wil
There are three related parameters involved:
- Number of pixels in your image (e.g. 2000 x 3000)
- ppi value (e.g. 300 ppi or 72 ppi)
- image size value (e.g. 8" x 12")
For example if you have 3000 pixels on the long size and an image size value set to 8" x 12", then the ppi is (by math) 3000 / 12" = 250ppi.So, all these values are related. You can set two of them and the third must be calculated via math.
Now, only ONE of these values actually affects the bits of the image and that's the number of pixels. Neither Smugmug nor web browsers nor Smugmug's printers use either the ppi or the image size value so the ONLY thing that matters to them is the actual number of pixels.
The ppi and/or image size values are not really properties of the image itself since they have nothing to do with the image bits. They are merely pieces of metadata on the image. One could set the ppi to anything you wanted and the image bits wouldn't change at all.
When you upload a high pixel number image to Smugmug (let's say it's 2000 x 3000 pixels), Smugmug looks at that image and sees that that is too many pixels for a typical screen size. So, it creates a bunch of smaller versions of the image (fewer pixels) using downsize algorithms. It will create up to six smaller versions that are used for web display. These smaller versions just have fewer pixels so they fit in smaller spaces on the screen. In all of these the dpi and image size don't matter at all.
There is one time that ppi and image size might matter. In a program like Photoshop, if you set the ppi with the right (or wrong) settings, it might also cause the image to resize, thus changing the actual number of pixels in the image. In most cases, you should NOT do this. You don't want to go upscaling or downrezzing your image without a really good reason for doing so because each time you do so, you potentially lose image detail. There are ways of changing either the image size or ppi in Photoshop without changing the number of pixels at all. This is just changing the metadata on the file and has no impact on the pixels or on web display.
All that said, I can think of no reason when using modern tools to care at all about either the ppi or image size labels that are stamped on your image. They don't affect web display, they don't affect printing, either at home or on Smugmug. Only how many pixels you actually have matter out of these three.
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Well...that clears things up!
Thanks.
I wrote a bit about image size and pixels here
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Glad to see I have company. Welcome aboard. See comment by Tony Cooper, seems to answer it, but we'll see what else is posted here.
Thanks for jumping in.
Many thanks. Website mods primarily use requires JPEGs to be less than 600K, apparently doesn't do its own adjusting. So to do this I use PS Image menue, and "Save for web ..." in File menu. In Image menue, I select last option ("bicubic sharpener, best for reduction", an obvious downward resampling), and through experience in setting image size, usually get 520-580k JPEG in "Save for web ..." while still maintianing 96%+ quality. Is any of that contrary to what you wrote? Is there a better path for my specific client use?
Again, mamy thanks.
Many thanks. Thought I had it understood and still think I do, but I'll do homework on your material. Never can be too sure.
The question is, what "size" do you want this to appear on this display? If your display actually outputs 72ppi and you size a JPEG to 72x72, you'll get a 1x1 inch image on that display. But not all displays output at 72ppi. They vary widely these days.
To find out the actual PPI of YOUR display, simply measure the width and divide that by the horizontal pixels that your system should report to you. For example, my NEC 3090 is 25" horizontally and I drive it at 2560x1600. So its output resolution is 102.4ppi. IF I wanted my image to appear 1x1, 72ppi wouldn't fly.
Since posting images to the web means anyone and everyone with differing displays will view them, its a guess in terms of exact size so 72ppi is probably fine, but assuming you expect a fixed size, all bets are off. We also don't know if people will be using an ancient 17" CRT or a new 30" LCD, so obviously you can't size images too big.
Author "Color Management for Photographers"
http://www.digitaldog.net/
800 x 1200 pixels - 600 ppi
800 x 1200 pixels - 72 ppi
and put them on a screen that they fit on, there will no difference between these two images on screen. The browser displays the pixels - that's it. The pixels are identical.
The ppi is just a piece of metadata on the image and it is NOT used by the browser when displaying the image at all. You can completely ignore the value without any issue whatsover. If you try to manipulate the ppi value and cause the pixels to get changed (assidentally or on purpose), you will probably be degrading your image when you did not have to.
Furthermore, if you are printing the image to a specific size (e.g. 6x9 or 9x12 or whatever), again the ppi in the image metadata is not used at all and does not matter.
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There are two parts to the original poster's question. First, the need for uploading a file for monitor viewing with a ppi of more than 72. Second, the (implied) question of the best way to get a file to conform to a maximum size requirement.
Let's keep it simple and say you have a 3008 x 2000 pixel .jpg image right out of the camera. No need to crop it all. The file size is 1.79 mb. You want to reduce the image to get to under 600 kb to meet the max size requirement.
What's the best way to get the photo under 600 kb? Choices include a width in pixels to fit most screens and a compression setting.
Question of my own added: If the max size is 600 kb, but the submitted image is 200 kb, is the 200 version in any way inferior to the 600 version?
This is for viewing on a monitor.
http://tonycooper.smugmug.com/
Or, if the context for the image is not pure image viewing, but a typical browser window and something that will fit in a regular web page, then you probably want an image that's less than 700px on the long side. So, anyway, figure out how many pixels you want the image to be and reduce the image to that many pixels using a high quality scaling tool. Then, sharpen the image appropriately since a reduced image usually needs to be sharpened some more.
Then, save it at a JPEG quality level of 8 (on the 1-12 Photoshop scale) and see how large your image is. Level 8 should be more than enough compression quality for display purposes. If your image fits the size you need, then you're done. If your image is still too big, then you have to either decide to reduce the pixels further or you have to go with more JPEG compression. At this point, it's pretty image-specific and situation-specific to know which is best. If you are pretty sure you like the size (number of pixels) you have, then try a lower quality level number. Try JPEG 5 or 6 depending upon how far off you are from your target and see what it looks like in a browser.
If you're submitting an image for evaluation and they allow you 600kb, then you are probably going to have a better looking image at 600kb than 200kb because you could use much lower compression. The only time that wouldn't make a difference is if the requested number of pixels is so low that a low compression value fits into 200kb. In most cases a JPEG compression level 8 will look better than a JPEG compression level 4 and in some instances the difference will be dramatic. So, if you're submitting something for visual evaluation, you should use all the space you have at least up to level 8 and maybe even go to level 10 if it fits.
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You still need to define the pixel dimensions unless you're asking, "I want a 3008x2000 pixel image but I want it to take up less space on a drive" in which case, you can JPEG the hell out of it. IOW, you are missing the important connection between size and pixel dimensions in the above question because you say you want a smaller file but do you want this at the same pixel dimensions?
Author "Color Management for Photographers"
http://www.digitaldog.net/
I didn't say I wanted to keep a 3008 x 2000 image. I said I wanted to reduce the image. The correct answer, of course, is to set the longest dimension at some figure you consider viewable on most screens (ie: 800, 1200, 1400) and adjust the compression if needed. I was curious to see if others would come up with some way I hadn't thought of.
http://tonycooper.smugmug.com/
Its only the right answer now that you've clearly defined what you want.
You can "reduce the image" only by either reducing the number of pixels (so we need to know this) OR by compressing the image or both.
Author "Color Management for Photographers"
http://www.digitaldog.net/
Which leads to another interesting question (or dumb question, depends on ones point of view). Do I get better uploaded JPEG screen resolution by relying more on reducing pixels in the ACR "Image/image size" pop-up, or reducing "quality" % in the "save for web ..." pop-up? The way I do it now, after setting "Bicubic sharper" and 72 ppi in the "Image/Image size" pop-up, is to make a guess at inch dimension in that pop-up which, in combination with a 95-100% setting in the "Save for web ..." pop-up, will produce a 500-600k JPEG file. I sometimes have to redo the inch dimension guess, but usually get it right.
On a related matter, my present screen is a 3 year old Dell 19" Ultrasharp. My next screen undoubtedly will be sharper, so do I continue to set "Image/Image size" resolution to 72 ppi for worldwide screen viewing uploads? I presume so. Am I missing something?
Now, and only now, you can decide what JPEG quality level you want to use when saving this downsized image. That depends totally on your intended use and the image and how much you're trying to optimize for slow download links. For small web images, JPEG quality level 5 or 6 is often fine. For larger images on the web with lots of fine detail, JPEG quality level 8 or 10 is sometimes appropriate.
As I have said several times, you can completely ignore dpi. If you are changing it or setting it, you may unintentionally be messing with the number of pixels in the image which is not how you want to be setting them. You should set them directly and let the ppi float to whatever it goes to. You really don't care what it is.
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Now to 800px long side results. This gets kind of long, appreciate whatever time you can devote to it. [1] Where longer side already was less than 800px, I didn't change anything on "Image Size" screen other than resolution to 72 (for screen viewing only) and re-sample to "Bicubic sharper". Correct procedure? [2] Where long side was higher than 800px, lowering to 800px generally resulted in a "Save for web ..." pop-up file size of under 600k at 100% JPEG quality, which is overall desired result. File size, however, often dropped to 300-450k, lower than my goal of near-600k, and JPEG quality sometimes to 85-90%, lower than my goal of 95%, to get down to near-600k. Am I correct that my former dickering with ppi (in the "Image size" box) and JPEG quality (in the "Save for web ..." pop-up) had the effect merely of up-sampling the image (adding pixels, reducing resolution) to get to desired goals of near 600k files at 95-100% JPEG quality, so what I'm doing now is getting rid of up-sampling, seemingly another desirable goal onto itself? [3] In practical terms, is 85% JPEG quality sometimes now resulting from 800px long side adjustment so low that I don't want to be there? My JPEG quality aim in "Save for web ..." pop-up has been solidly in the "Highest" or "Very high" range per box in that pop-up, where cut-off from "Very high" to plain old "High" is at 80%, near enough the 85% that I have to wonder. [4] I experimented with a few shots, left their higher-than-800px long side dimension at whatever it was, which resulted in approx 25% larger file sizes at same JPEG quality. Does this merely mean these experimental images will look better on larger than typical screen sizes, presumably with no up-sampling? [5] In low-crop high-contrast shots (typically mod in shaded light against strong open sun backlight), long side dimension generally begins at well above 800px before my px long side reduction. I'm having trouble thinking through why this is, with so much background burn out, I would have thought these shots' beginning long side dimension would have gone the other way. Comment? [6] For high contrast and colored shots with little crop, when I reduce long side dimension to 800px, I often then have to reduce JPEG quality to mid-80% to get down to near 600k file size aimed for, whereas under my old method of dickering with ppi I never had to settle for JPEG quality less than 95% for near 600k files. Is this merely a reflection of getting 95% quality of an up-sampled image (lower resolution, see 2 above), as opposed to 85% JPEG resolution of an un-sampled image, the latter possibly superior in resolution? Regardless of actual numbers, is my reasoning right on this?
Again, thanks for taking the time. Think I've now got it right, but that's what I thought before.
Stan
RovingEye
P.S. if you'd care to see samples of this latest set processed your way, please let me know your email address and I'll gladly send. They're not yet up on my Flickr or Smug Mug pages, way behind on uploading. Could use some independent processing valuation, good for the soul.