Hi Karl,
Wow, that's a lot of information to chew on... thanks for taking the
time to answer my questions so thoroughly, it is much appreciated. I'll
think through your answers for a while and may have to come back to you
on some of your points...
One point that immediately springs to mind though is about the resizing
if the composite elements (kids) - lowering the resolution to match the
background image; this is something I'd thought about doing but not how
you'd described. I'll try it and see what happens. Until now I've just
been re-sizing them to fit into the background 'scene' using Photoshops
Transform tool, mostly because I've been placing them in groups
interacting with one another at different perspectives within the
background image - the finished images are supposed to be tableaux of
historical scenes. I'd thought about using a filter of some kind to
degrade the quality somehow, to make them match the background, but I
guess altering the pixel size of each component would do it just as well
if not better.
The other point you made about the 'process' is interesting...starting
with a background image size at the final output dimensions. Again, I'd
thought about this but until recently we didn't really know what the
final print size would be. Also, the file size is so big that my
computer can't really cope with them... so I've been starting with the
background images as determined by the workflow option in photoshops RAW
window (at 12MP, 4256 x 3823, 300PPI) adding my re-sized composite
elements (cutout and re-sized with Transform) and then resizing the
whole image up to the required print size. This all seemed to go fine
until we printed an A3 cropped section from an image at 1600mm and
realised the background layer was not holding up, or at least, looked a
bit rubbish compared to the composited elements (kids).
I've tried starting with a bigger background image by changing the
workflow options in the RAW window to it's maximum (25MP, 6144 x 4088,
300PPI) and this seems to have helped, though there is still the issue
with background/composite disparity... so I'll try your suggestion of
re-sizing the kids to fit the background quality. Do you think it's
still important to start with the final output size though? Or even at a
quarter size perhaps?
Thanks again though, and I may have to come back with more questions...!
Just in case you're interested, the gallery who've commissioned this
piece of work have based the project on a show they had a year or so ago
by a fantastic photographer called Red Saunders. The tableaux we're
making are nowhere near as good as his, but have a look at his stuff to
get an idea of what we're trying to achieve;
http://www.redsaundersphoto.eu/1647.html
cheers,.
Jonathan
Jonathan Turner Photographer e: pictures@xxxxxxxxxxxxxxxxxxx t: 07796
470573 w: www.jonathan-turner.com
On 01/09/2014 16:14, karl shah-jenner wrote:
Jonathan Turner asks:
(questions that requiring pretty complicated answers, bear with me for
this long winded reply, or go to #1 for the short version below ;)
The point about viewing distance is a good point, which I
hadn't really considered.
Viewing distance has a heck of a lot to do with everything in
photography, up to and including lens choice when making the image.
Wide angle images which look all distorted can look perfectly normal
if enlarged to wall sized and you force the viewer to stand 2 feet
from the image - similarly a 1000mm telephoto shot which we normally
describe as 'compressed' will also look totally normal if printed
appropriately small OR you force the viewer to stand a long way back
(viewing angle the same).
Also, increasing the image size in 10%
increments is something I'd heard about
before but forgotten. I tried it
actually and I think it was was slightly better.
it should be slightly better, but not much - and if you experiment and
start with a clolour swatch you will find it eventually creates
patterns - highly undesirable. I illustrated that in the webpage I
liked but anyone can test it themselves, upsize in degrees until a
blindingly obvious pattern is created. resizing is bot a good way to
make things bigger, resampling is much better. As long as the
algorithm is appropriate (b-spline, s-spline, triangle, hermite,
Mitchell, Lanczoz, Bell, etc etc)
similarly downsizing (as opposed to downsampling) often creates
patterns - more often moire .. from unintelligent bit removal.
What you appear to need is some serious upsizing. If this were being
sent straight to print without mucxh manipulation, I would suggest
you'd be leaving the upsizing to a RIP, something that's been
discussed often in the past on this list. However the process of
incorporating image elements with differing levels of detail demand a
more complicated pathway.
The real issue though is the disparity between the background image and
the composite elements ...
see way down for more on this (#1)
as such I want to try and make the background image the best quality I
can to start with. So, I went back to the original RAW files, and
remembered that you can open them at different sizes/resolutions...at
the bottom of the RAW window in Photoshop you can specify the
dimensions/resolution and Bit depth you want to work with.
Photoshop is weird. I really wish they would stop mixing ancient
printing terminology like dots per square inch in (irrelevant) with
computer tech - pixels. Your image has a native resolution and if
shot RAW it'll be the full sensor size. I will asume it's a 12Mp
camera and that'd mean you have something like a 3k x 4k pixel
image. dpi is irrelevant BUT photoshop wants to know what sort of
silk screen you'll be squeezing your oil based ink through and thus
demands to the know the dot pitch frequency (bah) Tell it 300, then
check that your image is still only 3k x 4k pixels in size when it
opens the image.
Dimensions and resolution I understand,
I apologize if I come across as suggesting you may not - I've found a
lot of confusion starts and never gets past Photoshop forcing weird
conflicting concepts of 'resolution' on people so I try to define the
problem so we're on the same page ;)
though Bit depth is something
I'm unsure about...I have the choice of 8 or 16 bits,
simple answer is 'work in 16 bit'.
Bit depth is like the number of steps between absolutely no colour and
total colour. black (no clolour in transmitted) to white (all colour
in transmitted) - a bit of basics (sorry!)
if there are 4 steps you have black, dark grey, grey, light grey, white.
traditionally we have 1 bit (1 to the power of 2 or 1^2 = 2 colours..
ie, black/white)
2 bit (2^2 = 4 colours)
4 bit ( 2^4 =16 colours)
8 bit (2^8 = 256 colours) - this is a point where we
16 and above bit gets a bit weird, with some padding bits needed for
computational purposes being added in some cases (see here
http://en.wikipedia.org/wiki/Color_depth#High_color_.2815.2F16-bit.29
) but basically for editing, more is better - if your exposure is
damned good to start with and you're not going to stretch out the
tonal range, 8 bit is fine (no different from shooting E6) - and
although their are now printers that apprently work with 16 bit, I've
not seen the output and would suggest that while they might 'handle'
16 bit, they may (or may not, I truly have no idea) simply be data
converting and still printing using an 8 bit process.
What this is all about is how good our eyes are at perceiving the
transitions of colours - remember ever seeing pictures where the sky
broke up into distinct bands of colour? Often that was through
over-editing or more frequently, using a low bit depth image. If you
only have say 16 colours to represent the sky, it'll break up into
bands of colour to represent the closest colour available to reproduce
the actual sky colour. You don't see this much any more..
However it comes down to, the human eye is hard pressed to see discern
1/256th of a shade of colour difference in an image. ie, 8 bit (256
shades of individual colours) arranged in a line looks like a smooth
transition with no idividual patch standing out as being darker or
lighter. Actually it is hard pressed to see 50 gradation swatches in
mid tones, but eh.. 6 bit colour isn't really that mainstream (64
steps, and we actually can see gradations in tarker tones better than
lighter tones)
When it comes to image manipulation however, the more the merrier if
you need to wriggles those tones about. stretching out the tonal
range is a lot less likely to show banding if you have 65000 gradation
levels to expand out compared to 256. I could write 100 pages of
explanation but you'll see it yourself if you experiment..
and I'm presuming
if I choose 16 bits it will be better quality,
nope, just more of a gradation of tones between black and white, only
of use if you fiddle the levels enough to find banding occurring in 8
bit, and not in 16 bit.
I've tried using it and it
certainly increases the files size...so much so that when I have a final
composite psd the file size exceeds 2gb..
if I choose a higher resolution setting than
300PPI will that actually increase image quality?
I think you're fighting the Photoshop File Size Mangling Feature -
it's been an age since I fought this beast but the essence is that you
will probably find you have inadvertently resized the image and added
data. Let me see if I can remember howq this fight goes - I saw
students doing this often.. It kinda went like: Open a camera image
of say 3000x4000 pixels (which the camera may have tagged 72 dpi for
some insane reason), change the dpi to 300 (if you don't think this
through, your may find your image is now 12,500 x 16,667 pixels - 17x
bigger .. {or (300ppi /72ppi) squared bigger). Add a layer to that
and it gets worse, all of a sudden you're losing this battle.
300 pixels per inch (ppi) is an acceptable viewing resolution at
'normal viewing distance' (1/2 arms reach) for print - a compromise, a
general quality standard. heck, most monitors are only 90-140-ish)
(or 72 ppi if you talk of the early macs) At 300 print pixels per inch
most people don't see blocks - for some even 100 is OK, but truth is,
cut out or blank one line of pixels in an image (or add one line of
white pixels) and even at 1200 pixel resolution you'll see it. heck,
drop a line from a 4800 dot per inch (dpi) printer with a blocked jet
and you'll see it. but that's a line and we recognise repetition (and
lines) better than teeny individual dots.
Any good tips for improving overall base image quality much appreciated.
Just to re-cap; the images are composites with a final output size of
around 1600mm x 1064mm.
you're looking at around 64 x 42 inch image. I'll use inches since
we're using dpi (ppi) even though I'm a metric person myself.. so the
ideal image size that you will be sending to print in pixels is
300(ppi) x 64 inch times 300 (ppi) x 42 inch or 19,200 pixel x 12,600
pixels, or 241 Mp. Something I think may exceed your camera's
original output ;)
(#1 - the process)
So basically you are starting off this process by upsizing your image
to final print size, preferably using an appropriate upsampling
algorithm - save this file. it's big (241 Mp), then forget it for now.
Next we need to discuss 'resolution' in terms of resolving power and
not how many image elements exist in a given dimension (which is how
resolution is usually discussed in digital photography). and this is
the dilema you're facing - you have nice sharp face pictures you're
trying to insert on a background that is slightly less sharp and you
want it to look natural -
Resolution is the ability of the system to resolve detail. Like say
you shoot an image and oh yes, the back looks like a nice white wall
in image A, but in image B the camera was able to 'resolve' the
background and you notice it's not a plain white wall, it's actually
tiled and the individual tiles can be discerned. How it was resolved
may be a better lens, less shake, a different focal point, a different
aperture - whatever.. it may even have been a different media.. say a
finer grained film with higher capacity for resolving (resolution) -
Putting these pictures together is going to be tricky as you know,
much as mixing 70mm film and 8mm film would be tricky.. The way to do
it is you've got to work to your limiting resolution, ie the
background picture. Now you can either do it fiddling about and just
seeing what looks right, or you can do it mathematically, or a
combination of the two (have a rough mathematical idea and fiddle it
from there until, it looks right.. this will probably work best :)
Basically, it's back to the viewing angles!
this will get complicated because of my uncertainty about the original
image sizes .. but basically you have a grainy low res background and
sharp, high res bods to overlay.. so you need to lower the res on the
foreground kids to match the best quality you can get out of the
background image!
And i'll warn from seeing many many bad examples of this, mixing
camera lens focal lengths can make this a nightmarish task due to the
perspective conflicts (see those many actress shots where the
photographer used a slight wide and stood close giving her a giant
head atop a diminishing body and teeny feet -try putting that on a
'normal' background at your peril!)
Your limit of resolution is your original background image, upsized to
19k x 12.6 pixels. Although this is your final image, you really need
to work with the original image size and ratios pertaining to that.
I'll assume all images were taken at 3000x4000 (12 Mp)
i'll try doing this with ratios and simple arithmetic ..
Your background let's say is a wall roughly 30 feet long shot from say
50 feet away - I'll assume a camera with a 'normal' focal length and
talk no more about the lenses involved. You plan on arranging your 6
(more? less?) kids in front of this. you have a 30 foot long wall
made up of 4000 dots, or 133 dots per foot.
how big is a kids face? probably 6 inches across maybe? so you only
want that kids face to be 1/2 x 133 dots wide - say 65 dots (pixels)
wide. (ie, you should be able to fit 61 faces across your 4000 pixel
wide, 30 foot wall. I'm guessing you maybe shot these kids at the
same resolution but at maybe 1/4 of the frame width in portrait mode -
so they might be 1/4 of 3000 pixels wide, say 750 pixels wide. So you
can see you need to downsample these face images in this example quite
a lot! 750 / 65 = 11.5.. Which means you want to downsample your
original 3000x4000 pixel images to (wait for it) 260 x 347 pixels ! -
Now I know that sounds horrendous, but this would match the
'resolution' of both images.
Having determined this I would procede to select the head
/body/whatever of each individual kid from the original image at full
resolution, cut the non essential image data (the non-kid part) then
resample the image down 11 fold rather than cutting out tiny images
from the small image. These can then be dropped as layers over your
background image (they should be the right size now if you calculated
correctly) and all told even though it'll look a little fuzzier than
you hoped, the images should match both in size and apparent
'graininess' (resolving power is matched)
hopefully I didnt make a dogs breakfast of the calculations but my
inclusion of the methodology should help guide you if I have
-karl
