Photoshop HDR camera response curve problems

[rishloo]

I am working on the photoshop high dynamic range (HDR) photo format for the first time. After merging into HDR format the picture seems like an negative image and i am not able to bring its original texture. Can somebody plz help me out.

[McQ]

Photoshop's HDR algorithm was unable to generate an accurate camera response curve
(how actual brightness maps to pixel values from the camera's sensor).

The most common reasons for this occurring are that: (A) you did not enter correct exposure information for one of the original photos, (B) the images were not properly registered (aligned) on top of each other or (C) if there was a significant change in lighting between exposures (such as cloud movement in your example). The only other cause I can think of if a really drastic or inverted tonal curve was applied using photoshop's HDR curves tool when converting (prior to the "merge to HDR" step).

[rishloo]

Your explanation, most probably is correct. If a photo is taken in a raw format and while changing it into jpeg, exposures are changed twice or thrice and hence saved in three different copies. Can they be merged to form an HDR image? Another problem that i face while merging, the dialog box says, "there is not enough dynamic range to merge these phots ". Why does that happen? Here are two different pics that i had tried to merge but was unable to:

[McQ]

Yep, an incorrect camera response curve was indeed the problem. You can certainly create an HDR from several images created from the same RAW file (at different exposure compensations), but you need to be sure photoshop is using the correct exposure information. In your case, Photoshop is reading the EXIF information of each file and assuming that they are at the same exposure (and not accounting for exposure compensation). This is confusing the algorithm because the brightness distribution should be identical. You need to change the option of "response curve" on the right from automatic to "load from file".

However, first you will need to create a camera resonse curve to load. This can be done by taking a series of 5 or so photos about 1-2 f-stops apart in exposure, and loading these into photoshop's HDR tool. Do not create an HDR, but instead select the "Save Response Curve As..." option. Once this has been saved, exit the HDR tool and reload the earlier two images. Select the file you just created in the "load from file" button.

[rishloo]

thanks a lot. You have really been a great help. I ll work on it and let you know. Thanks again and this is a wonderfull site. One more thing, where do i get the option of "response curve"? I am not able to find the option.

[rishloo]

To create an HDR, the sreps i follow is FILE- AUTOMATE- MERGE TO HDR and then it starts to merge the pictures. After i have opened the Merge to HDR window i browse and select the pictures. In between these steps i have not been able to find the camera respose curve opton. Plz let me know the options i ll have to go through

[McQ]

The camera response curve button should appear on the top right after you have selected the images and aligned them. This would mean that you have clicked file > automate > merge to hdr > (selected the images and clicked ok) > screen with camera response curve on top right.

On this same screen you will see the selected images and EV exposures listed below them on the left as a column.

[rishloo]

As per the steps given by you , after merging the images my winow looks like this and i am not able to find the camera response option. ( Plz look into the attachments for the picture preview)

[McQ]

Looks like this is a photoshop version issue. Here's another way to accomplish the same thing:

(1) strip out the exif information for each photo (this can be done by using "save for web...")
(2) load the images as before "file > automate > merge to hdr > (selected the images and clicked ok)"
(3) you should then see a dialogue window popup for "manually set EV" - this is where you can change the exposure parameters

Let me know if this still has issues.

Something else that I did not mention in the previous posts: these example images really do not require HDR. The higher exposure version captures pretty much all you want and shows it with a good tonal range.