Photoshop tutorial - The art of RAW conversion
As you will see in this tutorial , raw conversion
offers much more control over processing of images than jpegs
which are automatically processed within the camera parameter
settings. Instead of letting the camera decide settings, you can
make much better judgments yourself in the Photoshop raw converter,
which is an integral part of Photoshop CS onwards. it is also
available as a plug-in from the Adobe website for Photoshop 7.
Photoshop elements 3 also has a raw converter.
Firstly, what is a raw image ?
Many modern cameras have the ability to shoot "raw" images. A
raw image is frequently likened to the digital equivalent to a
film negative - it is raw camera data and is unreadable unless
you use a special programme to access it. The Photoshop software
or other raw converter such as Pixmantec Raw Shooter, Breeze Browser,
Capture One etc are examples of such software.
What is the benefit of shooting raw images?
The benefit of working with the raw data is that
you have an incredible degree of control. For example, the ability
to change the white balance post-capture means that the camera
can be permanently set to auto white balance - and you make the
adjustments in the processing. The exposure lattitude in raw is
also very large, and a surprisingly under-exposed (and to a lesser
degree over-exposed) image may be corrected in the raw conversion
process just as if you were going back in time to when the image
was shot - and having another go at getting the exposure right.
Raw images are uncompressed unlike jpegs which are lossy (throw
data away) in order to reduce file size. Quality is therefore
maximised. The sharpening of digital images is best done as the
very last step after conversion in Photoshop and after any cropping
or other image adjustments have been made. Raw allows for a no-sharpening
option which is perfect. Jpegs create compression artifacts -
visible in areas of high contrast - particularly after sharpening
if you view at 100% image size (actual pixels) . The cropped 100%
image of a chough below illustrates a white halo in the circled
area with strange squiggly jpeg artifacts in evidence.
Raw images are uncompressed, so there are no artifacts,
and sharpening is more resistant to creating halo effects. Images
can be processed at 16bit resolution and later reverted to 8 bit
as the last step before sharpening. This maintains the maximum
digital data in the image.
If you save a raw image, you can always go back to it at a later
date and re-convert it again if you feel that you now have more
experience and could do a better job. With a jpeg, what you see
is what you get - and you can only try to superimpose a damage
limitation exercise on the image by using Photoshop tools. If
you are working in 8 bit mode with a jpeg - open the levels dialogue
box and you you will see an intact histogram. Now make some adjustments
such as levels/hue and saturation and colour balance. Then take
another look at the histogram in levels (example below) and you
will see vertical lines (combing) throughout the histogram indicating
Do the same in raw - where you will be working at 16bit and you
will maintain a perfect histogram.
Don't forget to convert the file back to 8 bit before saving though
as it doubles the filesize.
NB Photoshop CS introduced the ability to work within the programme
at 16 bit. Earlier versions of Photoshop such as Photoshop 7 had
limited functionality with 16 bit images.
Are those enough reasons to start shooting raw ?
Is there a downside to shooting raw?
The downside is that raws take up more space on your memory card
than compressed jpegs, and when using a motordrive the camera's
buffer fills up quicker due to increased file size. Raw converters
used to operate slowly, but good ones like Photoshop and Pixmantec
have addressed this problem. Pretty well all all pros I speak
to use raw - so perhaps you should give it a go too. I aim through
this tutorial to describe the steps in converting a real image.
The image is of a white-footed sportive lemur peering out from
it's hole in a tree. I will assume that you have Photoshop CS
or CS2 or are using the raw plug-in in Photoshop 7. You may need
to download the latest camera software from the Adobe website
if you have a very recent make of camera which is not supported
in your version of Photoshop . Before we get going I am only going
to to explain how to do a single image conversion - Photoshop
can do batch conversions of images shot under similar conditions
to speed things up, but I don't intend to discuss that here. If
you think this all seems a bit long-winded, don't forget, that
you are going to be doing all the adjustments that you used to
do within Photoshop now, in the Photoshop raw converter instead.
All that remains to be done after conversion is to crop, sharpen
and convert back to 8 bit for saving.
SO HERE GOES!.....
The highlighted words below refer to Photoshop controls. Open
the Photoshop File Browser (by clicking on the
magnifying glass and a file icon at the top right of the screen)
browse for the folder containing the image you want to work on
and double click on the selected image thumbnail or preview. The
raw converter detects a raw image and the raw dialogue box opens
like the one below. The first thing to do is set up the window
just as I have done below.
Notice that the "Advanced" box
is selected, depth is set to 16 bits, colour
space to whatever you use (sRGB in my case), Resolution
is set to 300 ppi (ideal for printing), size (3504 x 2336) is
determined automatically according to your camera's resolution.
Ensure the preview box is ticked, and initially
start off with a magnification selected to fit
the image to the screen (in this case 16.1%) One final thing to
be done is to click the small circled arrow immediately below
the histogram. It is here that you will be able to save settings
that you use repeatedly to save time. Also, in preferences
I recommend selecting sidecar .xmp files - as this attaches a
little file which remembers previous image-specific conversions
for you. Finally, set Apply sharpening to preview
only - as it is best to sharpen after conversion and last thing
before saving. You won't have to do any of this again - it is
now all set for the future.
We are now going to work through the adjustment sliders
on the "Adjust" tab. Starting with the white balance.
We can alter this from the "As shot" setting
by moving the temperature slider. Move it side
to side and you will see that the image becomes cooler/bluer to
the left and warmer/redder to the right. Set it until it looks
how you would like it to. (In this case 4300 looked correct to
me). Next adjust the Tint control by eye until
the colours look natural with no colour casts.
Now things start to get really interesting - we are going to
adjust the exposure so that the highlights are
not overblown. Our aim is to get the histogram to fit the box
without chopping it off (clipping) at either end. This is very
similar to adjusting levels in Photoshop - but it is much better
to do it before conversion
You will notice that the image is a bit over-exposed in the highlights
because the camera has exposed for the subject at the expense
of the background. Ideally, I would have underexposed the shot
and used fill-in flash to reduce the contrast, but I didn't, so
now I just have to make the best of it.
Slide the exposure slider to the left until the histogram fits
into the box on the right. By reducing the exposure by -1.95 f
stops the histogram fits the box without clipping the highlights.
The highlights are improved but the image now looks too dark in
the mid-tones - but we will fix that in a moment.
Next we are going to adjust the shadows in a similar
way. The aim is to get the histogram to fit the box on the left
hand side this time. As you can see in the image above, the highlights
and shadows are now adjusted to nicely fit the box without clipping
either, so now let's adjust those mid-tones.
Using the brightness slider, I have moved it
to the right until 120 on the scale is reached, at which point
the image looked good to me. You will notice that by doing this,
the height of the histogram reduced accordingly. Make any fine
contrast adjustments with the contrast slider
next, and finally adjust saturation to get nice vibrant colours.
I have increased this to +10.
We have now finished the settings on the "Adjust"
tab, and can move onto the "Detail" tab. Sharpness
will be already set to preview only - you can adjust this to make
it easier to judge results from now on. as this image was set
at iso 400 there is the chance of a little colour noise (grain)
creeping in, so to make it easier to see, I suggest increasing
the size of the image to 200% - by clicking the small down arrow
next to the box which currently reads 16.1% in my example. Now
adjust the colour noise reduction slider until
the colour noise just disappears - don't overdo it or you will
soften the image. A tiny amount of Luminance smoothing
can help smooth out particularly grainy images. Once done, reset
the size of the image to fit on the screen as before.
click on the lens tab. This enables chromatic
aberration and vignetting of poor quality
lenses to be adjusted. There is nothing to be done with this example
image, but sometimes you may notice a little red or blue fringing,
particularly on wide angle shots toward the edges of the image.This
may be removed by adjusting the sliders.
Finally, click on the calibrate tab. I usually
leave all the sliders at the default settings of 0. However, in
my example I decided to increase the red saturation a touch to
bring out the colour of the lemur's eyes, and a touch of blue
to bring out the highlight colour in it's fur.
So at last we have made all our raw adjustments,
so click OK and the image will now automatically
open in Photoshop at 16 bit. You can now crop the image if you
wish, convert it back to 8 bit (Image>mode>8 bits per channel)
and then sharpen it with Unsharp mask (Filter>unsharp mask) .
It is now ready to be saved as a TIFF file with zero compression.
To read a tutorial on use of the unsharp
mask filter, please click here.
So this is our finished result ready for printing : (I added
my copyright mark as I am publishing the image on the web.)
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