Soft Light blend mode

[Marpel]

Hello,

I have recently been trying out the Composite Transform where I use the same image as the input and overlay images, with Soft Light as the blend mode. I have found the effect quite appealing for some images. However, I am not yet familiar enough with this particular process so am limited at this time to "guess and try". A Photoshop-specific book indicates for Overlay, Soft Light and Hard Light blend modes, the lighter tones of the overlay image lightens the input image, darker tones darken and 50% neutral tones cause no effect. Soft Light causes the least change, Hard Light the most and Overlay lands between the two. However, the book gives no details on the exact amount of change with each mode. I have tried a full dynamic range image and found the result too contrasty with the highlights getting blown and the darks blocking up, so am trying to figure out how to gauge the dynamic range of the image when processing out of RAW into a TIFF so when blended, the resultant image is within 0 - 255. So, a couple questions:

- I presume the lighter, and darker at the other end, a tone is the more drastic the effect?
- Is Soft Light similar to just bumping up contrast and saturation with perhaps a mask for mid-tones? Visually, it appears to affect saturation and contrast.
- Rather than using a mask for the high end of the highlights and low end of the shadows (similar to the 3 tone adjustment curves devised by Den, with a less steep drop off), is there a way I can, with some exactness, know where to extend/reduce the dynamic range of an image coming out of RAW so Soft Light blend will not blow the highlights or block up the shadows?

Any comments on issues I may be missing would also be appreciated.

Thanks,

Marv

[couman]

Marv,

Mathematical descriptions and examples for the various blend modes can be found at:

www.pegtop.net/delphi/articles/blendmodes

The nomenclature used there is that used by Adobe. The list includes the filter and subtractive filter modes of PWP (multiply and screen blend in Adobe speak)

[den]

Marv...

An important distinction is that these filters [blend modes] do not affect the dynamic range of an existing image as converted from RAW to a tiff... but rather the distrubution of tones/colors within the converted dynamic range based upon their R,G,B 16-bit [or 8-bit] values...

If when applying these filters to a full dynamic range image [0-->255], the highlight/shadow blocking you see is not extending the 0-->255 range but rather the increase of more closely similar highlight and shadow pixels in close proximity resulting in a loss of detail...

If this is happening, it could be an indication that the RAW conversion tiff version already has sufficient brightness, contrast, saturation [at least in the highlights/shadows] and that this post-processing step is not all that beneficial for this particular image ...or... that rather than using the Input image Amount at 100% and the Overlay image Amount at 100%... the Overlay Amount should be reduced to a preference where the loss of highlight/shadow detail is acceptable yet the added contrasts from the image's 50% tone [128] and changes in saturation is a global enhancement to the image as a "whole".

A mid-tone mask will map an image's dynamic tone range to provide added insurance and controls to prevent objectionable blocking of the highlights and shadows... ...and to confine the filter's full effect to the mid-tones...

If the image's midtones are mask white and the shadows/highlights are mask black, consider a Composite-SoftLight or HardLight transform where: Input image=Overlay image; Input Mask Amount white=black=100%; Overlay Amount = 100%. Move the Mask black slider left to decrease the loss of detail in the shadows/highlights to an acceptable level... ...a suggested mid-tone mask applied to the Input image could be a MaskTool-BrightnessCurve BrokenLine curve = [0,0], [5,0], [20,40], [50,100], [80,40], [95,0], [100,0] with an applied Blur=3 for a 3456x2304 sized image... Do not overlook reducing the Input Mask white Amount as well as not ALL IMAGES ARE CREATED EQUAL!!!

...and Yes... the SoftLight and HardLight filters are similar to applying a RGB BrightnessCurve balanced contrast 'S-curve' whose mid-point is the [50,50] or 128 Luminance of the image... ...and... ...where the Input image = the Overlay image and is in 'color'.

Incidently when using SoftLight and HardLight filters, one could use an 'Extract'-ed Luminance or HSV-V channel as the Overlay image to avoid changes in saturation contrasts should that be a preference...

[Marpel]

Bob,

Thanks for the link. Although I must admit, the formulas were a bit (read "a lot") over my head, the descriptions and especially the examples were helpful.

Den,

Thanks for the, as always, detailed response. It's good to know the blending does not cause the resultant image's D R to go beyond the 0 or 255 levels. I have tried your suggested mask curve points and things seem promising (although I think the 5,0 and 95,0 points are especially image dependent). Interesting point about using the extracted Luminance or HSV-V channel. Is this the same thing as what others (Photoshop-centric) refer to as a Luminance mask?

Thanks,

Marv

[den]

(1) The suggested mask I have found to be 'generic' regardless of an image's dynamic range, full or otherwise, and is biased to include slightly more of the 0-->20% shadow tone range; more of the highlight 80-->100% tone range; and more of the mid-tones, 20-->80% tone range... ...than from a more accurate mapping of an image's darker 0-->50% HSV-V [0-->128] tones and its lighter 50-->100% HSV-V [128-->255] tones that would be accomplished using a BrokenLine curve = [0,0], [50,100], [100,0].

Note: A small Blur is needed to blend mask edge artifacts that may be created at the [50,100] control point due to the mapping curve's tone reversal.

The biasing makes the mask white [mid-tones] and mask black [shadows/highlights] Amount controls more effective when used in the Composite-SoftLight or HardLight transform as described in my previous post.

The suggested mid-tone mask BrokenLine curve file in text form follows... Copy and 'save as' with a "*.crv.txt" name... PWP5's Mask Tool will load this "Shrpn-LCE_mid-tones.crv.txt" as a crv file in its text form... for PWP4 and earlier versions: change the extention to only a "*.crv" name.

Curve 1.0
npts 5
style linear
histexpand 0
point 0 13 0
point 1 51 102
point 2 128 255
point 3 204 102
point 4 242 0
end

Incidently, this mask has further uses to provide fine mask white/black Amount control to minimize the lighter half auras/halos when sharpening or when adding local contrast enhancement to an image; and when blending images where emphasis is needed more in the mid-tones than the shadows/highlights...

(2) Luminosity is the black/white [0-->100% or 0-->255 tones] map of a color image when using the RGB color space model which is PhotoShop's default color space model. It is defined in PWP as:

Luminance refers to the perceived brightness of a color. Since the human eye
is much more sensitive to some colors than others, the luminance of a color is
computed as a weighted average of its red, green, and blue components.

Luminance = 0.30*Red + 0.59*Green + 0.11*Blue

So yes, PhotoShop users could be using this b/w mapping as a basis for a mask.

PWP's default black/white map of a color image is the HSV-V channel of the HSV color space model... the MaskTool-BrightnessCurve's histogram is based upon this channel.

The two are nearly the same for most purposes... ...to create a Luminosity mask in PWP, Extract an image's Luminance channel, then open the MaskTool and create a mask on it for use with a transform...

[den]

Update regarding "<file name>.crv.txt" extensions and the ability to use 'as is' with PWP... ... a thanks to Doug who notified me that on his system that he had to delete the ".txt" and his system OS is newer than mine.

In any case... if the warning "illegal crv file" appears; delete the ".txt" file name extension.

[couman]

Update regarding "<file name>.crv.txt" extentions and the ability to use 'as is' with PWP... ... a thanks to Doug who notified me that on his system that he had to delete the ".txt" and his system OS is newer than mine.

In any case... if the warning "illegal crv file" appears; delete the ".txt" file name extention.

I think it depends on which text file editor you're using -- my MS Notepad appends ".txt" to all files that it saves. It's wise to check the filename and change the extension to ".crv", or ".fcrv", or whatever is appropriate for the particular PWP transformation.

[Charles2]

Perhaps this recipe does something like to goal of the original post:

• FullRange-HSL (might leave image badly desaturated; don't worry)
• make a mask by brightness, inverse diagonal
• Composite | Soft light through mask, amount to taste around 50%
• compensating contrast with a Brightness-RGB S-curve

[Marpel]

Charles2,

Thanks for your suggestion. I will give it a try and see what happens.

Marv