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cgardner
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Re: Just a pretty scene


ben egbert wrote:
I have sometimes used 120 for brightness which helps for printing, but I had a custom print profile made that matches a screen brightness of 150.


A printer profile has two roles in a color managed workflow: 1) fitting the file values to the gamut of the printer\'s paper and ink, taking into accout mechanical varialbes, and; 2) softproofing on the monitor to simulate how the image will look on the print.

The limiting factor when printing is the gamut the paper/ink create. It is what it is and it is, is better on some printers than others and is a DIFFERENT SHAPE than the gamut of RGB monitors.

What do I mean by shape? Color managed color is mathematically modeled and manipulated on the axes of the Lab coordinate system. The gamut of Lab was defined with testing in the 1930s as the range of color a \"standard observer\" (i.e., average human with no color vison defects) can detect.

The ColorSync utility in OSX allows comparision of gamuts as 3D wireframes. Here\'s the comparison of my iMac\'s calibration profile and the profile for HP glossy paper on the 8/C printer next to it, seen from the \"top\" and \"bottom\" of the color space along the \"L\" axis:







The areas where the screen gamut is hanging out are colors the monitor can display with more saturation than printer can match. The yellows and greens hanging outside the monitor\'s gamut are colors the printer can reproduce \"better\" than you\'ll ever see them on your screen — in absolute terms of color you can see.

That physical difference and the fact that the printer can reproduce some colors better than a monitor is the reason you don\'t want your default monitor calibration to match the printer. Note I said monitor match the print.

The advantage of a wide gamut monitor is that it can display more of the printer\'s gamut accurately. For example here\'s the same printer profile compared to AdobeRGB in 3D from the top and bottom of the L axis (north and south poles of 3D colorspace):







There are still a few colors the printer can print with more saturation than AdobeRGB can display accurately.

Most starting out think in opposite terms and come to FM asking: \"How can I get my printer to match my screen?\" The answer is, \"You can\'t\". The printer\'s gamut is what it is. You can\'t increase the max saturation of the color it will print, you are just messing with the balance and rendering of the less than 100% percentage of CYMK ink the printer can lay down on the paper.

If you have a less expensive monitor or laptop you aren\'t seeing how the file will look when printed because of the limits of the monitor and are more likely to make poor, uninformed decisions simply because you are flying in a cloud by instruments.

What calibrating your monitor does is balance the RGB pixels so 255,255,255 and 128,128,128 and 16,16,16 all look neutral. But neutral perceptually is a moving target because the brain adapts to expectations. If you calibrate the monitor to a D50 / 5000°K white point, which was common in graphic arts in the 90s it the WB and color will look the same as with a D65 white point because your brain will adapt your color perception. But if you were to take a file edited on a D50 monitor and display it on a D65 calibrated one then will look different. That was the source of the Mac vs PC debates in the early days. Macs used a \"paper white\" 5000°K white point, while PC monitors where usually uncalibrated with a native WP of 9000°K. The gamma on early Mac screens was adjusted for 1.8 vs 2.2 on a PC.

What sorted things out was everyone agreeing to the same standards for viewing files on screen: D65 with 2.2 gamma.

What sorted things out in commercial offset publishing was all printers and color separators proofing using SWOP or other standard inks and paper and adjusting press profiles from that standard baseline

But there is no standard baseline for digital printing because the gamut of each printer is different and it changes everytime a different paper stock is used.

If a printer is sent a 255,0,0 RGB file value the color management engine in the printer (printer manages color) or Photoshop will convert it to M=100% + Y=100%. How that looks will vary between printers because the use different pigments. So one part of the conversion is mapping the extremes of the file values to the limits of the printer\'s gamut.

The other part is getting the less saturated colors looking \"perceptually\" correct. If you have a 128,128,128 gray in the file you calibrate your montitor to make it look gray. What the printer profiling process does is print that 128,128.128 gray and figure out why in isn\'t being printed as gray when color manangement is turned off.

If you use the \"North America Web / Internet\" selection in the color setting preferences Photoshop inserts \"SWOP Web Coated\" as the default CYMK space. If you go to the color picker and enter 128,128,128 as the RGB coordinates you\'ll see 52% C, 43% M, 43% Y, 8% K as the \"recipe\" for \"SWOP middle Gray\". Note there is more Cyan required than Magenta or Yellow to achieve \"Gray Balance\".

Now go back to color setting and change the CYMK default to \"US Sheefeet Coated\" and then look at the CYMK equivalents for 128,128,128 RGB gray. They change to 48%, 37%, 37%, 5%. The balance of C vs Y/M is still unequal and the values are lower meaning less ink is needed to create the same shade gray on sheetfed vs web press.

The difference? The paper brightness and absorption characteristics. What is assumed, but not obvious with those presets is the the papers and inks being used to print the targets which created those profiles where SWOP and Sheetfed standard papers as defined in printing industry specs. It was the establishment of standards like SWOP that allowed an advertisement for Coke to wind up looking \"Coke Red\" regardless of the press it was printed on.

All of this is obvious to me because I worked in printing and started dealing with color management in the mid-70s long before digital. When you print you need to manage the color backwards from the press.

First you print a target with known values for max 100% CYMK — as much ink as the printer can put on the paper and without dripping off onto the floor — neutral R=G=B — and lighter color combinations.

The printed sheet is then evaluated with a colorimeter. The 128,128,128 RGB patch will look too red and too light in tone because of the pigment impurities so the profile creation software adds more Cyan and a bit of Black to the recipe for CYMK middle gray. Since the paper and inks are different for web vs sheetfed the recipe for gray and all the other less than max % colors wind up different.

The profiling process is the same for ink jet and photo printers. When you get a custom profile make you are asked to print a standard target which is sent off and read on the same type of analyze we used at the printing plant to profile our large presses.

The printer profile is the road map for shifting the colors. Printing 255 Red as 100% Y+M is pretty much a no brainer on any printer and paper. Were the profile is critical and varies with paper is getting the neutral grays and less saturated skintones looking the same on the print as on the screen PERCEPTUALLY.

When you put a print next to a monitor and compare them the will never match in absolute terms in the most saturated colors. But go back up and look at the 3D wireframes. See how most of the colors are overlapping? The overlap in the wireframe render means they are the same in both gamut and don\'t change much between screen and print.

So if you have a photo of a woman in a yellow dress and print it the face will look similar on print and screen but you should expect the color of the dress to change. Why? It is physically impossible for the printer to create a purple that is as saturated and bright as your RGB monitor




















Jul 30, 2012 at 07:04 AM





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