It appears that your hypothesis hasn't stood up to your own test case.
I took your four test images and combined them into a single composite
image for ease of testing. I created an 800 x 800 composite image
containing all four 300 x 300 squares. For the printing I used some
inexpensive glossy Kodak paper on my inexpensive HP D7560 (CMYK + photo
black). This paper has never been used on this printer before and there
is no profile for it. Even so the color squares look pretty good.
From your own description of expectations and my own view of my not so
keen eyes I expected the B&W 300 dpi test (1" squares) to show me just a
middle gray square with none of the lines resolved. My unaided eyes do
not show clearly resolved lines but neither to they show a simple gray
patch. My eyes clearly sense there is detail there that I can't quite
make out. That was a bit of a surprise since, by rights, at 300 dpi, I
don't think I'm supposed to be able to make out any detail. Next, from
examining the print with a low power 2-3X magnifier, it's clear that the
printer itself has clearly resolved the lines at 300 dpi.
Next I tried rezzing up the image to twice its size giving a 1600 x 1600
image with the lines spaced at 150 dpi. When that one is printed I can
clearly see the lines even from about 20" away using my "computer
glasses". Then I did another test reducing the resolution from the
original 300 dpi to 250 dpi. I chose that number since that's what Mpix
uses and I stopped sending prints there because of it. Once again I was
surprised that I can clearly see the lines at reading distance and
beyond at 250 dpi.
Adding the color patches makes the lines not quite so clear but doesn't
really change the result. I can still see what I saw in the B&W patches
but I have to look a bit more closely.
I guess I was also surprised that the inexpensive HP printer resolved
the 300 dpi on the paper. But it did show that it has other maladies.
There are periodic bright lines and dark lines spaced at probably what
is the print head width. Or it may be that the printer would prefer 288
dpi or some other unique integer number to line up with the native dot
spacing.
Anyhow my view of 300 dpi for print resolution is now not that it can be
reduced but perhaps might even need to be higher.
Chuck Norcutt
On 9/9/2010 12:50 AM, Ken Norton wrote:
> Here you go, Chuck.
>
> http://zone-10.com/cmsm/index.php?option=com_content&task=view&id=538&Itemid=1
>
> AG
>
>> I have no idea how to create a custom fill or brush in PhotoShop to do
>> what you describe but the image size you define for a 5D is
>> approximately the same as I'd see 1:1 on my screen. Tomorrow maybe I'll
>> try to do a proportionally sized print of a small cropped section.
>> On 9/8/2010 5:49 PM, Ken Norton wrote:
>>> Well, I've devised a little test. Create an image file--doesn't have
>>> to be big at all because we're just experimenting around and the
>>> output can be rather tiny. Create this image file of, say, 300x300
>>> pixels. Now create a custom fill or brush with alternating black and
>>> white lines. These lines are one pixel in width. Follow so far? While
>>> you are at it, you might as well create a few other squares like this
>>> with other colors.
>>>
>>> What you now have is one or more squares made up of white/black
>>> one-pixel lines. At 100% on screen they should be perfecty
>>> sharp-edged.
>>>
>>> Now print this at 300 ppi. Examine the print and tell me if you can
>>> make out the lines. Change resolution to 240 ppi. See the lines? Keep
>>> going down until you can make out the lines. Now tell me again that
>>> you NEED 300 ppi resolution from camera to printer. Most
>>> printers/inks/papers won't even SUPPORT 300 PPI resolution as there is
>>> too much bleed.
>>>
>>> In the film days you could figure a reasonable enlargement of 8x
>>> before the image resolution started dropping to the point where
>>> golden-eyes could see the difference. So, if you figure that a 300ppi
>>> print is equivalent to a "contact negative", you should be able to use
>>> a quality scaling tool to upres the photo to the equivalent to 8x
>>> before the image is hashed up enough to be problematic. But other than
>>> Genuine Fractiles, most scaling tools aren't anywhere near as good as
>>> optical enlargement, so chop that 8x in half. 4X is a nice round
>>> number. And amazingly enough, in my own tests, I've found that 4X
>>> enlargement from digital files (considering that 300ppi is equivalent
>>> to a contact negative) seems to be the point where my own eyes detect
>>> the resolution loss.
>>>
>>> Saying the above paragraph another way... Take your image file and
>>> uprez it 4x. Now when you print this at 300ppi, you're at the
>>> threshold where print quality, according to those with perfect vision
>>> will suffer. 8x uprezing is still fine for most general-purpose
>>> applications.
>>>
>>> To bring this full circle, the 5D, when using the 4X factor, allows
>>> for a print 38.8 inches in height. Inotherwords, you can make a 40x60"
>>> print that is essentially perfect to everybody except those with
>>> magnifying glasses.
>>>
>>> The 5D's native image height is 2912 which at 300ppi is the equivalent
>>> to a contact negative print 10x15" in size. This is why digital has
>>> passed film in the EFFECTIVE resolution department years ago. Because
>>> it isn't the capture side that is the limiting factor of output
>>> resolution, but it's the output side that is the limiting factor of
>>> output resolution.
>>>
>>> Back in the film days there were two reasons to shoot larger formats:
>>> enlargement and tonal smoothness. With the 5D, the native non-enlarged
>>> size is already almost 10x15" and tonalities is a non-issue as it
>>> doesn't change regardless of how big or small you make the print.
>>>
>>> AG (do the test, I dare you) Schnozz
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>
>
>
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