Capability of Blenders to cope with images exposure differences

As the PTStitcherNG new stitcher with integrated blender has come now in the field of panography, I wanted to know if it could face successfully a rare situation.

Test case:

One of the four individual fisheye images for stitching a panorama is out of the kind of the three others: it was shoot about half an hour later that early morning and with +4 ISO (i.e. 1600 Vs 100) to replace the original shot that was done.

And of course and as a consequence, this single photo was subsequently shot with a different and specific set of exposure settings:

These differences were compounded with a separate and independent conversion from the raw format into TIF in ACR.

The reason for this extravagant workflow was to dramatically increase the Depth of Field (DOF) of this specific image while maintening both the high shutter speed and the IQ of the low ISO images for the rest of the panorama. On this image, the single main (small) subject was situated at only about 30 centimeters from the digital sensor plane.

The four different images to be stitched

This is only an illustration of the order of the individual images: the four photographs have been cropped to be put one aside the next. Note that the fourth ("darker") image is astride equally on the two ends of the panorama (i.e. on the 360 deg. seam). This can be disastrous when blending is done by Photoshop CS4 Auto blend layers (see next paragraph). Theoutput panorama (360 x 180 deg.) image shall be finally shifted by 180 deg. to present the oddly exposed image at the center.

 

Photoshop CS4 Auto blend layers (1)

The panorama shows a strong color mismatch at its center when it is shifted by 180 deg.

Workaround: If the 180 deg. shift is done on the four layers BEFORE blending, the resulting blended panorama is rather good:

Photoshop CS4 Auto blend layers (2)

The mismatch of color has disappeared:)

Enblend

A slight difference from the previous case but IMO both equally acceptable.

Smartblend

Again a slight difference, but another acceptable answer.

PTGui internal Blending engine

Yet another very similar good result as before.

PTStitcherNG beta 07 (integrated blending)

PTStitcherNG does blend correctly the 360 deg. seam, but it cannot cope with the exposure difference and because the seam is a priori situated halfway between overlapping (warped) images. This feature may leave a "star like" pattern on skies at the Zenith and in the present specific (extravagant) case, there is a strong visible color difference between image #4 and the others.

Conclusion:

While this could also sometimes happen with PS CS4, PTStitcherNG is the only "blender" that could not render a clean panorama where the fourth stitched image is so differently exposed in comparison with the three others. It is not a surprise and is probably the low price to pay for benefiting of its blazing stitching 'n blending velocity. PTStitcherNG is so fast and good for common and normal cases (i.e. with near-equally "manually" exposed individual images) that it should be my favorite blender anyway.

Thanks again Helmut.

Michel Thoby

9 March 2010