HDR stands for High Dynamic Range, and it is a technique in which many images – usually around 3 or 5 – are merged together, so that details from all the different images show up in the final HDR image. It is simply using the dynamic range over many exposures in one single image.
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Photoshop is a great and very effective tool for merging the series of photos of the same scene you have taken, to give an HDR image with lots of details and tones. In this article, I will tell you how to take photos for merging them into an HDR image, and then how to use the photos for the actual process of making an HDR image in Photoshop.
How to take source images for a final HDR image
The logic behind an HDR image is this – one single photo cannot show all the details from the highlights and the shadows. But, if we over-expose an image (make it brighter), we start getting details from the shadow region. Also, if we under-expose an image (make it darker), we get details from the highlights. What if we could do both the things together ?
HDR, in simple words, is combining an over-exposed image with an under-exposed image and a few other photos of the same scene (just for having even more detail), so that we get one single photo with multiple light levels.
So, to take the source images – the ones you'll be combining – all you have to do is take the same photo with different exposure levels.
The best way to do this is to first fix your camera on a tripod and setup your composition. You don't want your camera moving, because then there will be no similar images to merge. Also, shoot in RAW for more latitude while processing the images in Photoshop, although the method works even for JPEGs.
Once your camera is ready, take a photo that is metered by the camera itself. Not under-exposed, not over-exposed. This image is your base image, and it is basically a photo that the camera will take if it was in Auto Mode.
Now, you need at least 2 more photos to merge them all into an HDR image. Change your shutter speed to change the exposure. If you change aperture, the depth of field will change, which will make some areas of your photo unwantedly blurry. Changing ISO is also possible, but try to avoid it so that you get a clean image with no noise.
Make sure you have an under-exposed image by 1 stop at least. You can also go further and take an image under-exposed by 2 stops. Do the same the other side. Over-expose the scene by a stop, and then by one more stop.
Now, you have 2 under-exposed, 2 over-exposed, and 1 base image. You could also have done this using an 'Auto Bracketing' feature if your camera has one. More the number of images, more the information available for the final merged HDR photo.
So, you have 5 images – or more – with different exposures, all with the same composition and still subjects. Keeping your camera stable is very important, otherwise the camera shake and movement of the subject will cause ghosting and will also make merging all images into one very tricky.
How to merge all images in Photoshop
Once you have the source images ready on your computer, you can open Photoshop and begin working on merging your images for HDR.
Merging HDR in Photoshop
1. Open Photoshop and choose File > Automate > Merge to HDR. Here, you will get the option of choosing all your source images.
2. If in case you are unsure about camera shake and think that there is some change in the composition in the source images, select the option “Automatically Align Source Images”.
3. When you click OK, the computer will process the files and you will have to wait for a few seconds. Now, choose the 32-bit depth for the highest amount of tonal range. 8-bit and 16-bit files cannot store the entire range of light.
4. Now, the image you will see is a 32-bit preview of the final image with the source images on the side. Check for some ghosting or weird movement in the shot and if there is any, remove the source image which has the movement in it.
5. The 32-bit preview has a lot of information, most of which your computer screen cannot show. So, make sure that you save this file for later use as a 32-bit (tiff, .pbm etc) HDR full of details.
6. The merged result is a floating-point 32-bit image. You can view the available tones by sliding the White Point slider. This slider won’t change the image, it is there for you to examine the range of tones, because a monitor is incapable of displaying the whole tonal range.
7. The 32-bit image will still seem darker than you may want, but once you convert it into a 16-bit or 8-bit image, it will start to look better. You'll need to use the 8-bit image for sharing and emailing and uploading it to social media.
8. Choose Image > Mode > 8-bit. Here, you'll get options to actually bring out the exact exposure you want. You’ll see an HDR Toning Dialog box, with 2 options – Exposure and Gamma.
9. If you want an image with lots of contrast, lower the gamma. For less contrast, raise the gamma. Finally, adjust the exposure to get the desired image. There will be other options like Local Adaptation, but these are advanced tools and need another article itself.
10. If you are happy with the image, just click OK and you are done. You can also make further edits like shadows, highlights and saturation. Experiment and try to see how these settings change your image.
This is all!