Sunday, December 7, 2014

An Expensive and a Free Way of Matching Screen and Print

A PHOTOGRAPHER ASKS: “When I make a print, it looks duller, grayer, and more bland than what I see on my computer monitor, even when I’m using soft proofing. Do you have any tips or advice on making the computer image match my prints?”

The range of colors — or gamut — that can be printed on a typical color printer is less than what can be displayed on a computer monitor, and so Photoshop and some other image editing software packages include a ‘soft proof’ tool which limits the colors on the screen to match the printer gamut. While this is a good way of checking color limits, very often people complain that the prints are much darker that what is seen on the screen. But this is to be expected, yes? You have a nice bright monitor lit by powerful lamps behind the screen while your prints are viewed under whatever dim lighting you might have in the room where you have your computer. Comparing these side-by-side is going to be disappointing.

The soft proofing will only be close to accurate if the brightness of what you see on the screen matches the brightness of the print — where the brightest white on the screen is equal to the brightest possible white you can see on a print. This is usually not the case with many monitors, which even at their dimmest setting is far brighter than typical ambient home of office lighting conditions.

However, it is considered good practice to turn down your monitor brightness enough to allow both comfortable editing and good print matching. This will probably get you 80% of the way towards good soft proofing and it costs you nothing. Any more physical accuracy will increase your costs and decrease your convenience dramatically.

Now if you turn up your lights in the computer’s room — or turn down the monitor brightness by a lot — then you might have so much glare on your screen to make editing it difficult. To correct for this, some folks will put a shield around their computer monitor, black on the inside, preventing much stray light from the room from hitting the screen — this is like a lens hood. You might be able to make one yourself out of cardboard and black spray paint.

This still might not allow a good match in brightness between your monitor and print, because as mentioned it might be quite impractical and undesirable to have the room brightness match your monitor brightness. In this case, imaging professionals will often use a ‘proof light box’, a good-sized enclosure where you can put your print, which has a number of presumably precisely-specified lamps inside of it which can be adjusted for brightness, and so can match the brightness of the monitor.

Using a light box allows for practical monitor brightness settings as well as desirable room brightness. However, this will not work well if the color of the lamps doesn’t match the monitor. The brightest white on the monitor ought to match the color of a pure white object in the light box, not only in brightness but in overall color cast, and so the right lamps need to be selected — but be aware that changing the brightness might very well change the color temperature of the lamps (common with incandescent lamps) —making your selection considerably more difficult.

However, you still may have a problem. A computer monitor has a multitude of red, green, and blue dots of colors, which can be mixed together in fine proportions in order to produce millions of colors of relatively good accuracy. On the contrary, the colors of a print are going to be strongly influenced by the spectral qualities of the lamp used to view it. If you don’t use a specially-made spectrally accurate lamp, the colors will very likely be different — sometimes greatly so — between the monitor and print, even though the tonality of dark and light neutrals might look the same. This problem is called metamerism failure.

This still might not give you an accurate match. The sRGB standard which defines the most common data format used in digital images specifies that images should be viewed surrounded by a dark gray surround — which will cause the eye to perceive shadow tones as being brighter than if they are surrounded by a white background. Photoshop does this normally, and your light box ought to have the same shade of gray surrounding your print. However, if you will eventually view your photo in a frame with a white matte around it, then you might want to edit the image with a brighter surround — and likewise evaluate the print with the same brightness surround. Also, be sure the view the print and computer image at the same size and distance.

Human eyes constantly adjust themselves to the lighting conditions, and so if there is a strong color cast in the room — say from bright, saturated paint on the walls — then your eyes will adjust, neutralizing the color a bit. This adjustment will effect your evaluation of the images, and will change your impression of the print under ambient conditions in the room, more than what you see on a bright monitor. For this reason, unsaturated colors in the computer’s room is desirable, and a medium gray is even more desirable.

Getting a good visual match between the monitor and print is going to be difficult and expensive. But there is an alternative. What I do is measure the brightness of the various parts of the image, using Photoshop’s dropper tool and by analyzing its histogram, and I adjust the values to give me what I know will be good values in the final print. Basically, I know, based on the measured color numbers on the digital image, what the colors will look like in the final print. I know that I don’t want the shadows to be too dark and adjust accordingly. If I need saturated colors, then I’ll use proofing and adjust the image to give me good bright colors without blowing out any of the ink values, which would lead to loss of detail and texture as well as shifts in hue. This ‘by the numbers’ method is accurate and highly predictable, and I really don’t need an accurate visual match on my screen. This is inexpensive but quite accurate, if somewhat difficult to do well. It also has the advantage that I know that my colors are right, even if I’m not seeing right at any given time, like when I’m tired.

1 comment:

Ted Cossins said...

Hi Mark,

In para.3 you say "Any more physical accuracy will increase your costs and convenience dramatically."

Should that be be "inconvenience"?