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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.

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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 missing data!

Levels


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.

Tips and tutorials - raw conversion 2

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.

Tips and tutorials - raw conversion 3

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.



Tips and tutorials - raw conversion 4


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.

Tips and tutorials - raw conversion 5

Next 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.

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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.

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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.

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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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