snapsy
Online
• • • • • •
Upload & Sell: On
|
Posted this on dpreview (link) and posting it here as well for my FM peeps  Including the Alt board on this thread since many there are looking for a smaller/lighting system solution that doesn't sacrifice IQ.
I recently acquired a J4 and a preliminary workflow for producing full-frame equivalent IQ (in terms of noise). There are two main aspects:
ETTR (Expose to the Right)
Exposing the scene so that the brightest highlights wanted/needed are near the rightmost edge of the raw data/histogram. Unfortunately the J4 doesn't provide an RGB histogram and its luminance histogram is imprecise because it's based on a JPEG tone curve (even when shooting raw). I haven't yet tried UniWB or altering the picture control to produce a more reliable histogram. For now I just calibrated the raw levels vs the J4's middle-gray exposure for my most-often shooting situation of landscapes. I've found that middle-gray + 3EV will yield a relatively-safe ETTR exposure, provided the sky is the brightest element of the scene, although you may find it safer to use +2.3EV or +2.6EV.
When shooting I have the camera's metering set to spot meter and the shooting mode to Creative-Manual. I meter the sky to bring the exposure scale to "0", then adjust the exposure to 3EV brighter than that. This is a little clumsy for repeated shooting but if you're taking multiple shots in the same lighting situation you only need to perform the metering once. A more convenient alternative would be to use Creative-Aperture Priority and keep the exposure compensation pegged to +3EV - that way the camera would always meter +3EV when you point to the sky. Unfortunately the J4 has a bug where exposure compensation to near saturation levels causes the meter to over-exposure by up to 2EV. Not sure if other 1-series bodies have this issue.
Image Stacking for noise reduction
In addition to ETTR I also shoot 20-shot burst for each photograph (you can use a 40-shot on the V3 for even better noise reduction). For this I set the mode dial to "Best Moment Capture" and the capture mode to "Active Selection". For the "Active Selection" option I use the "On release, record preceding frames". That way I can hold the shutter half-pressed and have all 20 frames captured when I release the shutter, producing less motion jerking of the camera. I have the "Capture 20 frames over" parameter set to 1/3 second instead of 1 second - you want to capture all 20 images as quickly as possible because even when using a fast shutter speed the camera is only able to read the sensor at 1/60. I set the "Frames saved(default)" to ALL so the camera defaults to store all 20 images of the burst.
Post-Processing
All 20 images are dropped into Photoshop ACR. I set the WB, sharpening and general adjustments on the first image, then synchronize the other 19 images to the first. I then click "done" and use File -> Scripts -> Load Files Into Stack. I click both "Attempt to Automatically Align Source Images" (since I shoot hand-held there are a few pixels of shift between images sometimes) and "Create Smart Object after Loading Layers". The script takes a few minutes to run. When done, I then go to Layer -> Smart Objects -> Stack Mode -> Median. That takes about 30 seconds. When done you can then crop the image to crop off any blank areas from any pixel shift between the 20 images - I intentionally do this after the Stack Mode because that fills in some of the missing pixels first. Note that a 20-image stack with median averaging reduces noise by 3.5 stops. A 40-image stack (V3) would reduce noise by 5.3 stops. AE bracketing/blending can achieve the same level of noise reduction and only require a few frames but the J-series doesn't support bracketing - plus the stacking technique is more suitable for High ISO hand-held situations as well.
Sample #1 Results
Here are the results of a sample scene. I used a J4 with the 10-30mm PD kit lens and for comparison, a D750 with a Tamron 24-70 VC. I set the aperture, shutter speed, and ISO the same for both bodies. Note that the ETTR on the D750 caused some highlight loss but I wanted to keep the exposure the same so that the noise comparison is fair to the D750. All had the ACR shadow slider increased to max +100 (for the bushes in the shade, simulating a High-DR scene), and all were sharpened in ACR with 35/35 and two passes of USM in PS (30/30/0 and then 300/0.5/0). The "Matrix" images were for the normal exposure that the camera would choose for matrix metering - in this case 1/1000. The spot-metered ETTR exposures were 1/160. Top row contains shadows (raised +100 in ACR), middle row has midtones and upper midtones, and bottom row is the sky. Click "Original Size" to see the full-size of these crops. "J4 Matrix", "J4 ETTR", "D750 Matrix", and "D750 ETTR" show the results from a single raw; the other two J4 images show the results for a 20-image stack.
100% Crops of 8MP downsampled images
Full-sized images (8MP):
J4 Matrix-Metered (single exposure)
J4 ETTR (single exposure)
J4 Matrix-Metered (20-image stack)
D750 Matrix-Metered (single exposure)
D750 ETTR (single exposure)
Sample #2 Results
This sample has framing better matched and more shadow areas to compare. All three images below are ETTR and the shadows raised in post-processing.
100% Crops of 8MP downsampled images
Full-sized images (8MP):
J4 (single exposure)
J4 20-image stack)
D750 (single exposure)
|
