Maintaining character of detail while down sizing image dimensions?

[earlybird]

Hi,
 Yesterday, in the evening, I made a picture of a desert scene that was lit in such a way to provide lots of intricate texture. I assembled a panoramic stitch and the master file measures approximately 9600 pixels high by 29000 pixels wide.
 I used Photoshop to down res the image to 2400x7200 pixels so I could make a JPEG preview copy, and found that the "details" became too "busy" and harsh. I do this sort of process often. but this time, because of frequency and lighting characteristics of the natural texture the image looked aggressively hyped. Viewing it made me uncomfortable.

 I had used a bit of Deconvolution sharpening and some slight contrast tweaking, but no output sharpening on the master file.

 I ended up using Topaz Detail to soften the small details after I down sized and before I saved to JPEG.

 I have tried to keep up with up res technologies, but this experience led me to wonder; are there any more advanced down res processes?

 Thank you.

[Bart_van_der_Wolf]

Hi,
 Yesterday, in the evening, I made a picture of a desert scene that was lit in such a way to provide lots of intricate texture. I assembled a panoramic stitch and the master file measures approximately 9600 pixels high by 29000 pixels wide.
 I used Photoshop to down res the image to 2400x7200 pixels so I could make a JPEG preview copy, and found that the "details" became too "busy" and harsh. I do this sort of process often. but this time, because of frequency and lighting characteristics of the natural texture the image looked aggressively hyped. Viewing it made me uncomfortable.

 I had used a bit of Deconvolution sharpening and some slight contrast tweaking, but no output sharpening on the master file.

 I ended up using Topaz Detail to soften the small details after I down sized and before I saved to JPEG.

 I have tried to keep up with up res technologies, but this experience led me to wonder; are there any more advanced down res processes?

 Thank you.

Hi,

What Panorama stitcher did you use? PTGUI offers a choice of downsampling algorithms (Lanczos2 (Sinc16) is probably a good choice). Even if you edited the pano in e.g. Photoshop, you could try re-importing the final result back in PTGUI, reducing the output size there and saving that without any adjustments.

Alternatively, you could try using Capture One. I don't know if it has a maximum file-dimension limit, but if you import the resulting pano and save at a smaller size it will do a good job. C1 uses some of the insights that were gained by my tests here on LuLa with writing an optimal up/downsampling heuristics by using ImageMagick functionality (https://forum.luminous-landscape.com/index.php?topic=91754.0)

Lightroom also has a good downsampling quality, but it has file-dimension limitations.

A crude way of downsampling in Photoshop would be to Gaussian pre-blur the image before doing downsampling with Bicubic. The blur radius would need to be dimensioned as radius = 0.25 * downsampling factor (reducing to 1/3rd of the dimensions, would be a factor of 3).

Algorithms that do not use optimized filters will produce downsampling artifacts such as aliasing.

Cheers,
Bart

[earlybird]

Hi Bart,
 I used the Merge process in Photoshop.

 Thank you for sharing all the suggestions. Your comments have given me the insight that I need to study up on down sampling and not take it for granted as I have in the past. I'll try to learn more about all the choices you have mentioned.

 Thank you.

[bernie west]

I tend to use bicubic (smooth gradients) for the resampling method in photoshop resize.  And then apply a smart sharpen to taste after that.  You might have used Bicubic Sharper method, which I find tends to do exactly what you said in your description.

[earlybird]

Hi,
 Thank you for the suggestion.

 I have been using Bicubic Automatic with the Photoshop Image Size command, which as you suggest defaults to Bicubic Sharper for downsizing.

 In my save to web dialog I have been using the standard Bicubic choice, without the additional processing.

 As this file was far too large to use in the Save for Web process I uses the Photoshop Image Size command and therefore used the Bicubic Sharpen method.

 Now that I am aware of the issue I intend to make better choices. The particular image I was working on really highlighted the issue for me, I never had occasion to see such an alarming change in character when down sizing images before encountering this particular example.


 I appreciate the help and explanations.

 Thank you.

[Bart_van_der_Wolf]

Hi,
 Thank you for the suggestion.

 I have been using Bicubic Automatic with the Photoshop Image Size command, which as you suggest defaults to Bicubic Sharper for downsizing.

Bicubic Sharper creates significant aliasing artifacts when used for downsampling without pre-blur.
https://www.bvdwolf.nl/foto/resample/down_sample.html

Cheers,
Bart

[Lightsmith]

You are downsizing two aspects of the image, taking it to few pixels but also going from 12-bit or 14-bit down to 8-bit with the JPEG format. There is no need to do that. I keep everything as 16-bit TIFF until they being converted for Web use.

For panos there are two great applications, PTGui and Autopano, each with their own strengths. Photoshop is a bit like a Swiss Army knife that has many tools but none that are the best in any given situation. Like the old Japanese saying "he has many knives, none sharp".