Pixels per inch for web
Posted by René | Filed under Photoshop, introduction, software, web
What is the significance?
Simply put? Nothing.
Well, if that were all I had to say on the subject, this would have to be my shortest blogpost ever… Okay, a bit more info then:
A lot of first time DSLR users are concerned that their shiny new camera delivers files that are “only” 72dpi, while their old point and shoot delivered 300dpi files. Why is this concern unwarranted? Surely 300 is more then 72, and more is better, right?
Wrong
The old wisdom saying is that “300dpi is for printing and 72dpi is for screen”.
There are a few things wrong with that.
First and foremost, the term “dpi” stands for dots per inch. In a digital file there are no dots, only pixels. So the correct term is pixels per inch (ppi).
Also, 72ppi originated as it was the resolution of an ancient Mac monitor. Current monitors have a much higher pixel density: My old 12″ PowerbookG4 for instance has a screen resolution of about 100ppi. Most current screens are somewhere between 80 and 120ppi.
Do the math…
for your screen: Simply measure width and height and divide the number of pixels by the measured values… Tip: Once you found the figure for your screen, be sure to enter it in the PSCS4 preferences under “Units and Rulers, Screen resolution”: That way, the “Zoom, Print size” will show an accurate sized preview.
So, is a 300ppi file better then a 72ppi file?
No difference
If you hadn’t gathered as much from the above, for display on screen, only the display you’re using will determine the “resolution”.
So, a file that contains for instance 500×750 pixels will be displayed at a different size (in inches, centimeters, or whatever you prefer), depending on the screen you’re using to view it. The arbitrary ppi figure set in the file has no relevance whatsoever.
To illustrate that, here is an example: Each file is 500×750 pixels. One is 72ppi, the other 300ppi.
Notice the difference? No? That’s because there isn’t any.
Why use it then?
Because you have to put something in the box: There is no way that Photoshop will allow you to not fill in a value. However, what you put in there is pretty arbitrary. Use whatever you like basically for display on screen.
I prefer to use 300ppi for general use, since then the “image size” dialog box will quickly tell me about how large I can print an image at decent quality. For web, I mostly use 72ppi (unless I forget) since, well, that’s what some people expect…
Some more reading: here
Tags: browser, dpi, PhotoshopCS4, ppi, Save for web, web
Photoshop CS4 Color Settings
Posted by René | Filed under Color Management, Photoshop, introduction, software
Once, and for all
Never thought I’d blog about something as individual as PS Color Settings… Then again, there is so much conflicting, incomplete or downright inaccurate info on the web, I thought it might be time to set the record straight.
Individual
First of: Like more things in photography life there is no “Magic Bullet”. If that’s what you are looking for, better get used to this idea: You need a basic understanding of Color Management.
On the bright side: The settings in the Color Settings dialog box affect a number of things. However, unless done totally wrong, how your images are displayed is not one of those things.
Settings nobody should use
There is no “Magic Bullet”, but there is a “one size fits no-one”: The setting called “Monitor Color”.
What does it do? Let’s go through the main problems step by step:
It sets your monitor profile as default working space. So every time you calibrate your monitor (you do that regularly, right?) your default working space changes. And your default working space is limited to your monitors gamut. Not good if you are on a laptop for instance.
One additional problem is that equal values for R, G and B might not give a neutral gray. And there are other problems.
One of those problems is, that it sets all color management policies to “off”. Note that, contrary to popular belief, setting “monitor profile” does not turn off color management altogether: The one good thing in all this mess is that you are presented with this dialogue box when opening an image with an embedded profile:
Damage
The damage you can do here is very real:
If you tick the top option (“Use the embedded profile”), no damage is done. The image will be shown correct, and all data is retained. Not bad at all.
If you pick option #2 (“Convert to working space”), irreversible damage is done: The pixels in the image will be converted (changed!) to your monitor profile. Color numbers are converted (so colors will display correctly), but all colors out of your monitors gamut will be clipped. Poof! Gone. Forever.
If you pick option #3 (“Discard the embedded profile”), at least you won’t be damaging the file on import as in option #2 (it’s reversible by assigning the correct profile). But you will not be seeing the image correctly. So any “color correction” you do will be incorrect. The fact that the color numbers aren’t changed is a moot point because of this: What you see definitely will not be what others see.
Other problems
Yet another problem is that, even if you use embedded profiles, you will get no warning when you copy-paste an image into a new document (which by default will not have an embedded profile), or into an image with a different working space: The colors will change. See option #3 above.
So, I see no reason for anyone to use it. Not even web designers. Yes, I know that lots of browsers are not color managed. However, there are not lots of people using your screen, are there?
The only reason to temporarily set it, is when you need to check whether Photoshop is using the correct monitor profile.
Better
Just about any of the other “presets” is better. These presets are grouped in a few categories. When you scroll trough them, you might notice a few things:
There are settings for Europe and North America. And in every region there are 3 settings: for “General Purpose”, “Prepress” and “Web/Internet”. When you tick “more options” Japan appears, which has the same trio but adds “Color For Newspaper” and “Japan Magazine Advertisement Color”. There also appear a few other “international” presets.
Rather then going into each one in depth, I’ll generally explain some differences and possible pitfalls: They are “presets”, but IMO none is perfect. You can use them as a starting point however.
I start of with “more options” unchecked. And the screenshots are for the European presets. However, the comments I give are the same for the other localisations.
General Purpose
It Isn’t. It’s really that simple. Like I said: There’s no magic bullet.
Main drawback is that you get no warning whatsoever for profile mismatches: When you open two images in a different working space, and paste one into the other, colors will be converted. Which, as said, is irreversible and might give irreversible damage. If I’m going to damage my image, I damn well want to be notified.
Prepress
Is quite a decent choice if you are doing prepress work. Profiles are preserved, you are warned when you get a mismatch, and reasonable profiles are chosen for CMYK, gray and spot. (depending on the area you chose, CMYK and dot gain are different.) Then again, if you are doing prepress work, I’d hope that you know enough about color management that you don’t need to read my thoughts on it…
Web/Internet
This is the only preset where converting to working space might make sense in my opinion: If you are just doing work for internet, anything should be sRGB. If you have to ask why: Read my blogpost on the subject. Then again, I’d like a warning if an image has no embedded profile: In some cases it might be because someone screwed up. This is largely a personal preference however.
Other presets
Are “more of the same” (two other Japanese presets only differ in CMYK, gray and spot from Japan Prepress2). The “Phase One” workflow is the odd one out: It sets a gray profile of Gray Gamma 2.2 which is quite sensible. Then again, the CMYK profile is “Euro-Catalog”, which I never need.
The other options (Colorsync (mac only), PS5) are obsolete legacy.
Create your own
Since everybody’s needs are different, it makes sense to make your own preset then, doesn’t it? Sure! But you need to know what each setting does. Some things are pretty straight forward, others not so much.
Default working spaces: RGB
Pretty much up to personal preference. The question “what RGB color space is best” I’ll leave be for now. Use whatever working space you use in your raw converter of choice. Two points I do want to make: If you don’t understand color management, do yourself a favor and use sRGB as a working space everywhere. On the other hand, if you are using a wide gamut color space (anything larger then AdobeRGB) do so in 16 bit per channel only!
Settings never to use are AppleRGB, ColorMatchRGB or GenericRGB. These are based on monitors that went the way of the dodo…
CMYK and others
For CMYK working space: Most people won’t ever print something on an offset press, so won’t ever be needing CMYK. When you do need it, make sure the printer tells you what profile to use, and set that as the default: It has some impact further down the road in PSCS4.
Don’t ever use GenericCMYK or one of the “old” Photoshop CMYK settings here: No good reason to. When in doubt, you probably won’t ever need it, so pick the “default” for your region.
Same goes for Gray and Spot working space. If you do a lot of grayscale images for web, gamma 2.2 is the best setting. If you print them to a specific Offsetpress and you know what dot gain to use, by all means do. But in that case you probably wouldn’t be reading this article… For same reasons as above never, ever use Gamma 1.8. It’s obsolete.
Policies and Notifications
Choose “Preserve Embedded Profiles”, unless as explained above, you are a web designer and have thought about the subject a bit.
I don’t see the need to tick the “Profile mismatch: Ask when opening” box, since I edit images from a known source, and the embedded profiles are what they are for a reason. So YMMV. I do tick the “Ask when pasting” and “missing profiles” boxes. The first because I want to be notified if an image profile is converted, the second because if there is no profile embedded, someone screwed up.
Note that if you choose “Discard the embedded profile (do not color manage)” here, the image will be shown as if it had the default working space embedded. This has the same effect as assigning your default working space: The image won’t display accurate, but it is reversible (by assigning the proper profile).
Another note (a big one) is that PS somehow doesn’t display this warning when pasting an image without profile into a document with an embedded color space! Colors will change.
Advanced: Conversion options
Engine: Leave at “Adobe (ACE)”. It’s the best choice, and if you have a specific reason why you would want to use another, you would not need my advice.
Rendering intent: Either perceptual or relative colorimetric for photographic images. Which is best will depend on the image. Not that this setting matters much: This is the rendering intent used by default when you go Image > Convert to profile (where you can change it in the dialog box) and it is used when going Image > Mode > CMYK for instance (which I would strongly advise against, since it offers no preview and no direct control)
The description says it all:
Always tick “Use Black point compensation” and also “Use Dither”: It makes banding or posterization much less likely.
The last option “Compensate for Screen -referred profiles” is only important if you make documents for Adobe After Effects. In that case: Tick it. Otherwise: Tick it as well, since it won’t matter then.
Advanced, but not to be used
“Desaturate Monitor Colors By” and “Blend RGB Colors Using Gamma”: Easy: Don’t tick those. They are not meant for photographers. Again: Read the description:
Possible pitfalls
As already mentioned, the settings set in the “Conversion options” will be used when changing from one color space to the next by going Image > Mode. So do not go there. Use Edit > Convert to profile instead. Yes you can also use it to convert from RGB to CMYK…
Another, less well known fact, is that the default profile is what determines the values in the info palette (Color picker) for anything but the color space the image is in. So if you use a CMYK or grayscale color picker on an RGB image, the readout will be for your current default CMYK or gray working space!
Another of the stupid less-then-brilliant decisions on Adobes part was to have the Select > Color Range > Out of Gamut selection be based on the default CMYK working space. Makes no sense whatsoever and makes the tool all but unusable for anyone who prints at home, but there it is…
Here is an sRGB image, softproofed for my Epson R2880, using glossy paper. The Gamut warning is on and shows no out of gamut colors. Notice the selection?
Conclusion
After reading this, you should know enough about the subject to create your own settings. After you did, save them as your own preset. It might also be a good idea to add a description.
Here’s mine:
Tags: Color Management, PhotoshopCS4, WYSIWYG
Printing to an Epson R2880. Theory and practice
Posted by René | Filed under Color Management, Epson, Photoshop, printing
The “5-95%” rule
In a thread on Photography-on-the.net a while ago, someone mentioned reading some advise to set black and white point to 5% and 95% respectively. That’s approximately RGB values (12,12,12) and (242,242,242). Otherwise, shadow and highlight detail would be lost in print.
My first thought was “no way”. After all, white is 255, right? I’d say that’s what printing colormanaged and .icc profiles are for.
I’d accept a bit of a loss, but not thàt much…
So I started to search the web.
Whàt?
One source of the advise was at www.lynda.com: Prepress Essentials by Taz Tally.
He was talking about offset printing. There was also an example about Newsprint. According to that, for a (hypothetical) example where the newspaper press could print a minimum white highlight dot of 20% and a maximum shadow below 80%. The tutorial proceeded to adjust output levels similar to this:
According to the tutorial, you’d be preserving highlight and shadow detail as much as possible for those particular presses.
Yeah, right. What highlights and shadows? They all became midtones…
Gray
I’ve taken a black and white image of mine, since that tutorial was also using a b&w image, and adjusted the shadow and highlight values according to that tutorial. The red dots in the middle image represent the picked black and white point.
Negative scan of Popa Chubby in Atak, 1995. Left to right: Original, for “commercial press” and for “newspaper press”:
If I softproof the rightmost image for “Japan Color 2000 Newspaper” (the only “newspaper” profile I could find in PSCS4), it goes to hell in a handbasket…
Frankly, my first thought was the author went nuts.
Then again, this is Lynda.com, right? Maybe I just misunderstood. Or the file was sent straight to the newspaper press? (without color management)
Another tutorial
“Desktop Printing Techniques” by Chris Orwig, also on Lynda.com, made one point clearer: The 5 and 95% figures are a starting point, and you should test with your own printer / paper / profile. That makes perfect sense.
He also mentioned “accurate detail” and “relevant white / black detail”, where Taz Tally mentions it, but then sets black and white points that I would let clip: Mr. Orwig is more rational in picking the points he chooses for the color sampler tool. (Not the first highlight appearing, but actually something that you want detail in.)
Okay. Obvious: If you have blown whites, then guess what: They are not meant to show detail. No point in setting a white highlight at (242,242,242) nor a deep black shadow at (12,12,12). But that makes it quite personal: What is “meaningful detail”?
A few “Gotcha’s”
The tutorial then goes on to set the color sampler values to read out as grayscale.
No idea why, and not the best option IMO, since the “gray” readout in the info palette is dependant on the settings in the PS color settings for “Gray”.
And guess what: “Europe general purpose” uses Dot gain 15% where “North America general purpose” uses Dot gain 20% for gray working space. Not a huge difference in this case, but one to know.
Also, why not just use the RGB (or HSB) values? They remain constant whatever color settings. Better yet, use LAB values: They change as the luminance changes: quite a difference between (12,12,12) in sRGB and the same value in AdobeRGB (Give it a try)! So keep in mind your document color space!
The “Gotcha’s” visualised
To demonstrate those issues, here are a few screenshots of 4 color samplers I placed in 4 neutral gray patches of a document (the test print I’ll use later on).
All this also speaks in favour of doing your own tests: Your workflow is probably different from mine, or that of the Lynda.com instructors for that matter. As is your definition of “meaningfull detail”.
Let’s stop theorising already!
As easy said as done.
So off to search the web for a test image.
I found this nice test image (and description how to evaluate the print) here
Test print: some thoughts.
I usually use AdobeRGB.
The image is in ProPhotoRGB, which gives the “number” patches a little different meaning: A ProPhotoRGB value of (6,6,6) I can distinguish quite well from pure black. In an AdobeRGB document, I have to look hard. In an sRGB document, it’s quite obvious. Similar, ProPhotoRGB (253,253,253) is less easy to distinguish from pure white to me then the same value in AdobeRGB, while sRGB is easiest. The differences are quite subtle though.
The LAB color pickers came in handy here: I wasn’t going nuts, there is a slight difference.
Now that is cleared up…
Lets get printing
I used the Epson R2880 with Epson Premium Glossy Photo Paper.
Color settings in PSCS2 printing dialog:
Colormanagement off in the printer driver of course.
I used the .icc profile downloaded from the Epson website.
There is one profile provided for that paper. The printer driver however, has a few settings that might influence how much ink is laid down on paper:
Photo – 1440dpi vs. SuperPhoto – 5760dpi and “high speed” on or off.
I decided to use an extra sheer of paper to see what the differences were.
I first printed 5760dpi with High Speed on (since I never turn that off anyway) using Relative colorimetric and Perceptual. Black Point Compensation was turned on.
Relative Colorimetric vs. Perceptual
In this test image, the biggest difference is that Relative Colorimetric was a bit more saturated in red and green, but showed blue a bit more purple. Maybe because of that, purples also look a bit more saturated. Unexpected (to me) was that oranges seemed actually more saturated using Perceptual.
Relative colorimetric (with BPC) has a touch less separation between absolute black and (6,6,6)
The softproof showed all of these differences as well.
So I decided to use Perceptual for the second set of prints: 1440dpi with High Speed on and off.
What were the differences?
Not a heck of a lot. In all “Perceptual” prints (6,6,6) is barely visible. And I do mean barely. Relative colorimetric is a touch darker even: It’s more of a “I think I might see a difference” there. I cannot see (4,4,4) in any of them.
I don’t think I see a visible difference between 1440dpi and 5760 dpi, nor between high speed on or off. Yes, I did use a loupe.
Maybe the absolute black is a tiny bit denser if 5760 or “High Speed off” is used, but frankly, I’m not sure (comparing the two absolute black patches in the top right, holding them right next to each other in good light).
A measuring device would be needed to make sure. This is also the “I think I might want to see a difference” category.
The grayscale image is neutral to my eye. There might be tiny color shifts in the dark patches, but that could be my eyes playing tricks. If you need absolute neutrality you might want to test, but for my uses, the B&W is excellent.
No use in posting (scans of) prints, since you really need to see this for yourself. Take my word on this.
So. What did I learn?
The softproof is surprisingly accurate.
I cannot distinguish anything darker then L=1 (LAB color picker) in print.
I cannot distinguish anything lighter then L=99 (LAB color picker) in print.
That is ProPhotoRGB (6,6,6) and ProPhotoRGB (252,252,252) respectively.
That’s fairly close to what I see on screen on my CRT in the highlights, with a bit loss of detail in the shadows. I might want to compensate for that.
A good way to do that is described in this video by John Paul Caponigro.
If I have an image with very deep and important shadows, I might try a test print. But for my normal (even critical) printing, I can trust the softproof: If I see detail on screen, I’ll see it in print. And I’m not all that concerned about the absolute deepest maximum black. Since I don’t consistently see the difference anyway.
Conclusion
I certainly do not want to limit myself to a brightest highlight of 95% for my inkjet printing. So I’ll take the 95% in the tutorials with a grain of salt. I did find, when examining a random bunch of images I processed using my normal workflow, that most images have meaningful detail at about that value. So the tutorials at Lynda.com are right in a way, but could be more accurate.
I’m still very much in doubt on the “Newspaper Press” image that more or less caused this blogpost however…
If anyone has good info on that, I’m all ears.
Further reading
Some excellent resources on printing and related stuff:
http://www.johnpaulcaponigro.com/downloads/technique/technique.php#printing
http://www.northlight-images.co.uk/article_pages/black_and_white_test.html
http://www.northlight-images.co.uk/article_pages/test_images.html
http://www.outbackprint.com/printinginsights/pi049/essay.html
http://homepage.mac.com/billatkinson/FileSharing2.html
Tags: Color Management, Epson, Preview, printing, WYSIWYG
