C. C. Varner
Stretching Sequence for No Data Loss
The top left image is a stacked image of the Running Man Nebula using 66 300-second sub-images. The details of capturing this image are in the image called Running Man (NGC 1977) 5.6 h. This is the unstreached color image that has been color balanced by Nebulosity 4.0. Its histogram is shown in the upper left corner.
The upper right image is the original stack image that is scaled up by Nebulosity 4 using the Levels tool and setting its power to 0.14. Its shows that the light signal has be moved to the right (increased) by the scaling. None of the signal has been lost -- just brightened.
The middle left image is stretched from the upper right one by adjusting the black point up to 39000, which is about 4000 points below the first indications of signal of the target signal. This stretches the image without causing a loss of signal information.
This process is repeated several times: After the 4th stretch, the peak in the histogram has been spread over a large portion the histogram of this image (blue line in the middle image on the right). When this image is pushed right (moving the Levels power to 0.14) for the 5th time, a double hump is observed in the histogram. The small first hump is an indication that the image is banding.
For the 5th black point adjustment, the black point is being set at 45000, which causes no loss of signal because the bottom of the signal is a few thousand point above this black point. This image can be exported as a JPEG image for final cleanup in Adobe Photoshop.
Stretching Sequence for No Data Loss
The top left image is a stacked image of the Running Man Nebula using 66 300-second sub-images. The details of capturing this image are in the image called Running Man (NGC 1977) 5.6 h. This is the unstreached color image that has been color balanced by Nebulosity 4.0. Its histogram is shown in the upper left corner.
The upper right image is the original stack image that is scaled up by Nebulosity 4 using the Levels tool and setting its power to 0.14. Its shows that the light signal has be moved to the right (increased) by the scaling. None of the signal has been lost -- just brightened.
The middle left image is stretched from the upper right one by adjusting the black point up to 39000, which is about 4000 points below the first indications of signal of the target signal. This stretches the image without causing a loss of signal information.
This process is repeated several times: After the 4th stretch, the peak in the histogram has been spread over a large portion the histogram of this image (blue line in the middle image on the right). When this image is pushed right (moving the Levels power to 0.14) for the 5th time, a double hump is observed in the histogram. The small first hump is an indication that the image is banding.
For the 5th black point adjustment, the black point is being set at 45000, which causes no loss of signal because the bottom of the signal is a few thousand point above this black point. This image can be exported as a JPEG image for final cleanup in Adobe Photoshop.