Angstrom Studio

HDR: the beginning, shooting

2010-03-22T02:09:00.000-03:00

As can be seen on the Picture 2 and 3, the dynamic range of the camera is pretty poor. It depends on the sensor, the CCD sensors have the dynamic range about twice higher than the CMOS. It also depends on the output format of the camera, which usually is JPG.
There are two ways to get an HDR image:
>from (usually) three images (one with normal exposition, one overexposed and one underexposed). Later these images are joined using specific software. I used Photoshop (CS2 or later), Photomatix and Dynamic Photo HDR. From my personal point of view Dynamic Photo HDR is far better then the other two. Photoshop and Photomatix don't give u much control on the final image processing.
>from a single RAW file. I will treat a more detailed processing of RAW files in a separate section.

The first method consists in shooting three consecutive photos of the same object with different exposure levels. The best way to achieve it is to use exposure bracketing. Most cameras have it. The most usual range of exposure levels is from -2 to +2, but in some cases it is convenient to use lower ranges, like -1,7 to +1,7 or even -1,33 to +1,33. The last range may be recommendable in cases when you're shooting white, like a statue, in conditions of small light contrast. The results may be interesting, like shown in the Figure X (CORRECT PICTURE TO FIGURE AND PUT NUMBERS). It is always recommended to use a tripod while shooting these three pictures, because they must be almost perfectly aligned. You will have a very good advantage if you use the Dynamic Photo HDR for processing, because it has a wonderful tool that allows you to manually align the images. It means that if you didn't use tripod, the small relative displacements of the photos and even rotations, can be corrected manually. Automatic alignement doesn't always do it right. VERY IMPORTANT: Always make sure that the only difference between the pictures is the exposure time, because if you vary ISO you will get noise and if you vary the aperture you will have different depth of field on the three pictures and that may lead to ugly results. Also it's a good idea to use exposure bracketing instead of manually changing the exposure. It's faster and easier.

RAW and HDR

2010-03-22T02:05:00.001-03:00

Since RAW images contain much information, one could think that it could be possible to get an HDR image from that. Quite right. When processing a RAW in the CameraRaw, itis quite easy to get a beautiful HDR, it's just matter of taste. Also you can import a RAW into the Dynamic Photo HDR and get a great results. But. It's important not to push too much the capabilities of the RAW. If you're trying to take a picture of a scene with very bright zones (like a white or almost white wall directly iluminated by the sun) and at the same time with very dark shadows, a single RAW shot will probably be useless. There won't be information about the wall (it will look like a plain white) nor about the shadows (that will look like a plain black). In that case it would be a better idea to take several shots with enough exposure range to cover all light intensities. Probably taking 4 or 5 JPG shots will be equivalet to taking 2 RAWs. I never tries it and it came to my mind while typing this. If anybody tries it, leave a comment.

RAW: some basics

2010-03-21T13:57:00.000-03:00

RAW is an image format that saves the information that comes directly from the sensor of the camera without procesisng it. That means lots of information available to play with. The JPG format is an 8-bit format, that means that it has 8 bits per channel, ergo 256 levels of colour per channel (three basic colour plus brightness). That makes about 16,7 million colours, which is more than human eye can distinguish. But it's not enough if you want to do some serious editing. The RAW format has about 10-14 bits depth, wich depends on a camera. That gives you a lot more information to play with.
The best soft to process the RAW images is the Adobe CameraRaw, which is a plugin for Photoshop. There are many other programs that can read and edit raw, but the CameraRaw is just the best. I can say that because i tried many others, and you can also read the same in many forums.

HDR: some important tips

2010-03-21T13:30:00.001-03:00

There are some important things i learned during my experience. Some are quite obious, some not that obvious.
> Denoise images before processing them: always. If you are using a compact camera, not a reflex, even in lowets ISO there is some noise. When merged into HDR and processed, usually that noise is amplified, turning the resulting image quite ugly. Besides, that noise is pretty strong and very hard to remove. But if you filter the images before processing them, there almost won't be any noise to be amplified. There are several programs fir noise filtering. I use the PureImage, by Mediachance, the same who did the Dynaimc Photo HDR. Photoshop's denoising abilities are pretty poor.
>Despite Dynamic Photo HDR allows you to align the images (displacement and rotation), it is always recommended to use a tripod. The handheld shots usually introduce distorsions, because of the rotation of the camera in all three possible directions.
>Use HDR only when there is a strong contrast of light in your scene. If your scene has a nice homogeneous lighting, trying to do and HDR is pointless. The overexposed and the underexposed images are supposed to add information on the zones that are too dark and too bright respectively.

If something else comes to my mind, I'll add it.

HDR: processind, software

2010-03-21T12:54:00.001-03:00

Once you have the pictures, the next step is to merge them into an HDR image. For that you need some software. If you have Photoshop CS2 or higher, you can use it, but there are much better software, specifically designed for HDR. The two best programs are the Dynamic Photo HDR (the one i always use) and the PhotomatixPro. I tried the last one a couple of times, but i didn't like it as much as i liked the Dynamic Photo HDR. From my experience i can say that Photoshop should be used for HDR merging only in cases of not having anything better, or in case of emergency because it allows very little control on the color settings.
This post is not aimed to be a detaled manual about usage of the previously mentioned software, but I'll give you some short instructions about how to get started.
Photoshop:
When the program is running, go to File > Automate > HDR merging... A new window opens and there you'll be able to importa the photos to merge. -------------------------
Dynamic Photo HDR:
When the progam is running, go to File > New. You'll see a window. Press "Add Images" and select the photos you want to merge. Press Ok. The next window will show you the superposition of the photos and will allow you to manually align them. For detailed instruction about alignment, read Help. When you're done aligning, press Ok and the program will generate the HDR image. When the program is done working, it will show you the result. It won't be anything spectacular at all. Don't worry. That image you will see, contains too much colour information to ve showed by any hardware that exists by now. What you can do is to play with all that information. To do so, press "Tone map HDR". It opens a new window and that's when the stuff gets really cool. On the left upper side there are several ways of mapping, with their respective adjustments under them. On the right there is more, but they are universal (that controls apply to all mapping types). If you press the button over the Gamma slider, you'll have a nice selection of filters. If you want to know more, check the manual.
Photomatix Pro:
Sincerelly, i used it just a couple of times and i didn't like it. Basically, it's used in the same way: import, process and save results. Check the manual or use the try-and-see-what-happens method.

Introduction

2010-01-11T23:36:00.000-03:00

Welcome.
I dedicate this blog to my greatest passion: the photography.
In this blog i'm going to share all i know about photography and computer treatment of images. I will concentrate most in the following topics:
> HDR photography: from taking photos to some software usage tips
>Macrophotography: general stuff
>General photography tips
>Some general image treating tips in Photoshop CS3
>For users of Canon compact and bridge cameras: CHDK, a must-have software, general information

English is not my primary language, so if you find mistakes in this blog, please let me know.
Also let me know if u think that some information i provide is not completely correct.

HDR: why

2009-12-27T21:53:00.001-03:00

First of all: what is HDR?
HDR stands for High Dynamic Range. The dynamic range is the range of light intensity from the intensity recognized as black to the intensity recognized es white. It's a property of an eye, a camera sensor, etc. It has nothing to do with the blurry effect on the edges, very popular in the last computer games. The human eye has a very high dynamic range, that's why we can stand inside a dark room looking outside, where is sunny, and notice that the room looks just a little darker than the outside. On the other hand, if we take our camera and take a picture, we'll get an overexposed outside or an underexposed inside, depending on where we measure the light intensity, on an inside wall or on something on the other side of the window. On the next three pictures i show you what i mean. (INSERTAR IMAGENES DE VENTANA) On the Picture 1 we can see the previously described situation as our eye sees it. On the other hand, the pictures 2 and 3 show the over and underexposed photos, respectively. On the Picture 4 i show schematically the idea of dynamic range.
The HDRI (High Dynamic Range Imaging) also can give us some beautiful results, like shown on Picture 5.
In this section i'm going to explain how to get these results.