Overview

If you're interested in using Bryce to create photo-realistic images you may have run into the situation where you've finished a scene, taken great care with the objects, textures and lighting, but the finished result just doesn't quite "look" right. Sometimes this is simply a perception.

The eye perceives a particular field of view when viewing a natural landscape and expects to see certain proportions and angles in an image created with traditional photographic equipment. The expectation is a completely learned response from a lifetime of examples. Compare a photograph taken with a 35mm camera to one taken of exactly the same subject at exactly the same time by a digital camera. Digital cameras are a relatively new invention and use different optics than traditional photographic equipment. When I look at these two images, 40 years of experience makes me perceive the digital image as different.

Photographers have also developed certain practices to compensate for the limitations of the equipment available to them. In some cases, they will deliberately distort an image to achieve a particular style or mood. As an example, I've always admired the work of Ansel Adams but there is little chance of me recreating his style with a 35mm camera even if I managed to master all of the other artistic elements of his work.

The end result is that if you don't present the eye with what it expects to see, your finished image may quietly "look" wrong. Fortunately the Bryce render engine has the ability to precisely recreate these proportions, it's just a matter of knowing what the eye expects.

Field of View

The field of view value is set in decimal degrees but you're probably more familiar with the field of view of a particular lens. The default value is 60 degrees and that corresponds to a wide angle lens. A sensible enough default for an application that was originally intended to create images of natural landscapes.

If you remember a little geometry and have a pocket calculator you can work out the angles exactly.

For the 35mm format the exposed film area is:
h = 24mm

w = 36mm

d = sqrt( w^2 + h^2)

  = 43.27mm
f = focal length of the lens in mm
horizontal angle of view = 2 * arctan (w/(2*f))

vertical angle of view   = 2 * arctan (h/(2*f))

diagonal angle of view   = 2 * arctan (d/(2*f))
Convert radians to degress:
degrees = 180 * radians / pi

The reference table lists some common lenses and their angle of view for the 35mm format. Find the lens you want to reproduce on the left and enter the decimal value from the (Horizontal) column in the FOV field of the camera dialog.

f (mm) Angle of View (degrees) (Apparent
Zoom)
(Horizontal)
(Vertical)
(Diagonal)
Wide Angle 7
137.4990
119.4871
144.1394
0.33
8
132.0750
112.6199
139.4112
0.34
14
104.2500
81.2026
114.1821
0.44
15
100.3889
77.3196
110.5270
0.45
16
96.7329
73.7398
107.0267
0.47
17
93.2732
70.4352
103.6777
0.49
20
83.9744
61.9275
94.4932
0.54
24
73.7398
53.1301
84.0622
0.62
28
65.4705
46.3972
75.3806
0.69
35
54.4322
37.8493
63.4400
0.83
Normal 43
45.4288
31.1856
53.4140
1.00
50
39.5978
26.9915
46.7930
1.15
55
36.2437
24.6160
42.9427
1.25
Telephoto 85
23.9132
16.0714
28.5583
1.90
100
20.4079
13.6855
24.4137
2.23
135
15.1893
10.1592
18.2081
2.99
150
13.6855
9.1478
16.4135
3.32
200
10.2855
6.8673
12.3470
4.42
300
6.8673
4.5812
8.2490
6.62
400
5.1531
3.4367
6.1915
8.82
600
3.4367
2.2915
4.1299
13.22
800
2.5779
1.7187
3.0980
17.62
1000
2.0624
1.3750
2.4786
22.03
1200
1.7187
1.1459
2.0656
26.43

Document Aspect

Since you can only set the horizontal field of view you need to adjust the vertical field of view indirectly by changing the document's aspect ratio. In the 35mm film format, the exposed film area is 36mm wide by 24mm high or 3:2. Match the aspect ratio in the document dialog by setting the aspect ratio directly or click on the Photo button.

Printing

If the final image is to be printed, you need to be aware of the document resolution as well. For images destined for the web, simply choose a convenient size.

I use two print services. I like Shutterfly for prints up to 8x10 because their process (near as I can tell) creates a continuous tone image. For larger prints I use ez prints because their quality is excellent and they offer larger format prints.

Crop or Fit

When you print you may have to crop the image depending on the final size.

Format Aspect Ratio
36mm x 24mm 1.5
4 x 6 1.5
5 x 7 1.4
8 x 10 1.25

The gray areas show how the original image will be cropped. This isn't a problem since both the film image and the virtual image will be cropped in the same manner.

Print services will generally give you the option of cropping or fitting (stretching) the image to match the final print size. While you'll lose some of the image with cropping, always select this option because it maintains a uniform scale.

Document Resolution

Both services I use give the best results with an image resolution of 100 to 150dpi, with the file uploaded in the maximum quality JPEG format. You can send  higher resolutions or use better file formats but you won't be able to see the difference and one way or another it'll be more expensive.

If we take the 8x10 print as an example, we know the image will be cropped on the left and right sides. To make sure we'll have enough resolution in the height direction we use that dimension to calculate our Bryce document size.

8 inches x 110 dots per inch = 880 dots (pixels) high

880 pixels x 3 / 2 = 1320 pixels wide

Since we're throwing away pixels on the left and right sides when we crop the image we need to compensate by increasing the width. If we used the width to determine the resolution we would only have about 92dpi after cropping.

An easy way to remember is to always use the dimension adjacent to the crop line to determine the document resolution.

Color Corrections, Models, Gamma and Gamut

One thing to remember about any Internet print service is that they are most commonly used to print images taken by amateur photographers. They will typically apply some additional processing to an image before printing that you need to keep in mind.

Always check with the service to see if they do any automatic color correction. If they do, include a note along with the order instructing them to disable the automatic color correction before they print the image.

Sometimes people worry about the differences between the RGB and CYMK color models. If you're generating an image to be run on by an offset printing process, by all means, check with the printer. But for printing Bryce images with an Internet print service you generally don't need to concern yourself with such details. Services are used to receiving images in RGB format from digital cameras. If any conversion is necessary, they'll do that automatically.

Make sure your monitor is properly calibrated so that the image will print as expected. If you're using a Mac, be aware that your monitor's gamma correction will almost certainly make the printed image appear washed out if you're not careful. Before you order a large print, try ordering a smaller proof just to check the color and make the appropriate adjustments. Be careful to make sure that the proof will be printed on the same equipment as the full version.

Bryce is capable of generating a wider range of colors than most printing methods can reproduce. It's always a good idea to load the final image in an application like Photoshop and check for gamut warnings before you order. Here again, a proof can be very helpful.

Common Practices

Professional photographers commonly use different equipment and techniques for different situations. In general, the more you know about traditional photographic methods, the easier it will be to create photo-realistic images in Bryce.

Texts on these techniques are widely available online and at your local book store so I won't try to duplicate them here. Rather, in this series of tutorials, I'll focus on specific techniques and how they can be reproduced in Bryce.

As usual, send questions and comments to toad@castironflamingo.com.

Copyright 2002 - CJC, all rights reserved

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