How can I measure a print's brightness?

[TonyW]

I have been using a commercial printing firm for some time and they have produced good prints that fit my expectations. However, the last batch of four prints came out too dark My monitor is calibrated and I checked it afterwards and it was right, with a brightness of 119 candela/sq metre (if I have the units right). The recommended is 120.

Is there a way of actually measuring the print instead of just looking at it to see if it matches my digital image? The only way i can think of is to use a scanner which has been calibrated with a known print, if such a thing exists.

[Shadowman]

Tony,

Did you download the firm's ICC paper profiles and did you request a reprint?

[Manfred M]

Tony - I find 120 nits (a.k.a. candela / sq meter) far too bright for the prints that I do and I have to brighten them up before I print them. The recommendations I have read for computer screen brightness are between 80 - 120 nits, so you are at the high end of the range.

Some commercial labs brighten up images before printing, as part of their standard practice and others print them as the customer supplies them. Test prints are the only fool-proof solution I have found and am not aware of any standardized test for print brightness, nor can there be one. A night scene is going to have lower reflectance than a snow-scape.

I would discuss this with the lab(s) you are using to come up with a way of ensuring the prints you submit come out the way you expect.

[Shadowman]

You might consider using a spectrodensitometer. Not only will it measure ink density it will also measure the brightness using L*a*b*. You could also try using a lightbox to compare the print to the screen.

http://www.xrite.com/categories/port...hotometers/508

http://www.pixl.dk/produkt/lyskasser...htbox-xl3.html

[TonyW]

John and Manfred, thanks for your replies.

I haven't discussed the problem with the lab because I wanted to have some objective idea of how much the prints were out. I have been using the lab for a couple of years now and since I started calibrating my monitor I have had no problem with them until the last time. I will talk to them about the problem.

The photometer might be a good thing to use but perhaps not so easy or cheap to get hold of. It seems that the lightbox might be the best way to go. At least then I could have a side-by-side comparison of the screen and the print.

[Shadowman]

John and Manfred, thanks for your replies.

I haven't discussed the problem with the lab because I wanted to have some objective idea of how much the prints were out. I have been using the lab for a couple of years now and since I started calibrating my monitor I have had no problem with them until the last time. I will talk to them about the problem.

The photometer might be a good thing to use but perhaps not so easy or cheap to get hold of. It seems that the lightbox might be the best way to go. At least then I could have a side-by-side comparison of the screen and the print.

Tony,

Additionally, you could use the Info color picker set to HSB to determine the brightness on your screen. In the photo shown my cursor was on back portion of her shoe. Brightness of 100% and your blackest black should have no hue or saturation or 0%.

[Manfred M]

Tony have a look at the x-Rite document pertaining to evaluating prints:

https://www.xritephoto.com/documents...wingNTK_EN.pdf

There are standard lighting conditions - both colour temperature (D50 illuminant) illuminated by a 2000 lux light source that should be used to evaluate a print. The issue with a print is that you are using reflected light the view the image and you as the photographer need to determine exactly how you want the final print to look. I am not aware of any technical tool that can be used to suggest that a print is too light or too dark, as that is a judgement that the photographer needs to make. Professional viewing booths are extremely expensive and are usually not found outside of high end commercial applications. I don't know of any photographers that use one but have used these in a previous "life" in an industrial setting.

http://www.xrite.com/categories/light-booths

The fact that you have been using the same print lab for some period and you have been happy with their results suggests to me that there has been a mistake made by the lab or a policy change on how to handle customer prints. The only way to address this is to work with the lab. Qualifying test prints are the only way I know that achieves what you are trying to do.