QTR-Quadtone RIP

Hi.

This post is to let people know that a new file has been uploaded to 
the Files area of this site. The file 
(testimage_b&w_linearization.jpg) is intended to help users evaluate 
the linearization of monochrome printing setups.

Although I produced the uploaded file (it was a cold, wet Sunday 
afternoon) I can't claim to have originated the idea behind it : to 
the best of my knowledge, that honour belongs to Keith Cooper of 
Northlight Images (http://www.northlight-images.co.uk/) who included 
a small version of one of the targets in his own black and white test 
image. Keith has a lot of interesting stuff on his site, and I 
thoroughly recommend a visit to anyone who hasn't been there before.

As soon as I printed it, it was immediately obvious how effectively 
Keith's target showed up the problems in my profile, but I found his 
version too small to be really useful and I wanted to be able to 
relate what I could see to actual tonal values. Hence this test-file.

At the risk of stating the obvious, a quick heads-up for anyone who 
decides to make use of the test image . . . .

1) The step-wedges and stepped targets were created by posterising 
the gradients used for the non-stepped ramps. Anyone who's created 
their own step-wedge by this method will know that the posterizations 
are larger at the extremes than they are in the centre. (You can 
clearly see this effect in the linear 21-step wedge near the bottom 
of my test file.) In a sense this is helpful because it gives 
additional real-estate to the highlight and shadow tones, but it is 
done at the expense of the midtones. 

2) Because a circular gradient inevitably has a lot of perimeter, the 
circular targets with white on the outside will always (and should) 
appear much lighter overall than the targets with black on the 
outside.

3) Although we're all used to looking at linear gradients, circular 
ones take a bit of mental adjustment. I found that I only really 
began to make sense of what I was seeing when I printed using a 
couple of different profiles and compared the results.

And once I started to understand what my circular gradients were 
telling me, I came to realise that they're not very forgiving. It's 
important to keep in mind that any test image is a tool and not a 
picture : the important thing is to be happy with the final prints, 
not to produce a `perfect' linearization.

Finally . . . I should probably say that I'm not actually a QTR user 
myself, but (having trialed it a few weeks ago) it seemed to me that 
members of this group might find the test-image useful : I certainly 
hope so. I continue to watch the group because I definitely plan to 
use QTR when I get some new hardware, but as I'm unlikely to post 
again for some time, I'd like to take this opprtunity to congratulate 
Roy on a spectacular contribution to high-quality black and white 
printing. 

Graham Preston