Digital Light & Color

Hello,

I have noted, after using/trying a few different image editing programs over the years and reading related literature, that some "experts" suggest setting black and white points at around 8 - 9 and 248 - 249, respectively. In fact, a book I have on NX2, my current-used RAW program, suggests 9 and 249. I am trying to familiarize myself with PWPs RAW dialogue and see the Dynamic Range slider has a drop-down options box that allows not only "Full Range" but a couple others, including "Custom". However, the help manual does not seem to hold any info on this (it only briefly mentions "Full Range") and when I choose "Custom", it doesn't change the points on the scale, suggesting it is user customizable.

Can someone advise if "Custom" does allow the user to set the percentages to reflect 9 and 249 and, if so, how to do it?

Second, although related, question is - I presume if an image that has a lower dynamic range than 0 and 255 is put through the "Full Range" process, the tones are remapped (and expanded) to fit a full 0 through 255 (i.e. a foggy scene with a range of say 100 - 150 gets 100 remapped to 0, 150 remapped to 255 and everything in between gets expanded between the two). However, if an image that starts out with a range greater than 9 - 249 (say 0 - 255), has it's range changed to 9 - 249, do the pixels also get remapped and compressed (so the shape of the initial histogram between 9 - 249 actually changes) or do the tones between 0 - 9 and 249 - 255 just get clipped and become pure black and pure white (and the initial histogram between 9 - 249 stays the exact same shape)??

Thanks,

Marv

Dynamic range analyzes the input image and sets black and white sliders to the actual darkest and lightest pixels in the image. (Darkest and lightest pixels are determined from a histogram at the .01% frequency levels from the two extremes to prevent a few stray outlier pixels from biasing the results.)

Full range maps these darkest and lightest points in the input image to 0 and 255 (or 65536 in 48 bit images) in the output image.

If you want, you can move the sliders past the 0 and 255 marks. Depending on how far you move them, this can have the effect of setting the black and white points to the the 9..248 levels as you suggest. However there is nothing magic about the 9..248 numbers. The optimum settings will vary from image to image, so it is best to set them interactively while observing the effect in the preview.

Kiril

Kiril,

Thanks for your reply. I agree that each image requires its own evaluation as to it's optimum dynamic range. I think the 9 - 248 suggestions that I have read are more relevant to images destined for printing. Something to do with the dynamic range of photo papers I suspect. Regarding your comment about pushing the sliders past 0 and/or 255 to emulate 9 and 248, isn't it the other way and place the highlight slider lower than 100% (like about 95%) and the shadow higher than 0% (like about 5%)? If it is as you indicate, then I'm more confused about this stuff than I initially thought. Or by "past the 0 and 255 marks" do you mean closer together???

Also, where can I find info on the "Custom" drop down setting as noted in my initial post?

Thanks,

Marv

No, you actually do want to move the sliders beyond the zero and full scale values. For simplicity let's just talk about the black slider. However the same logic applies to the bright slider as well

The black slider indicates the darkest pixels in your image. If you place it at the zero point, the darkest pixel will have a brightness value of 0 in the output image. However the 9..248 recommendation says you should assign 0 to all pixels that have a brightness of less than about 4% (i.e. 9/255). To do that you want to move the slider into negative territory so that the 4% pixel will be at zero and the 0% pixel below zero. Of course no pixels can have a negative brightness. So what really happens is that all pixels below the threshold brightness are clipped to zero.

One justification for doing this is that these very low values are mostly noise, so what you are doing is taking these noise pixels and setting them to zero. This gives you nice solid shadows rather than wishy washy ones with no meaningful detail.

Custom simply means that the settings are not one of the choices on the drop down but are set by using the sliders. For instance if you choose Full Range, ths sliders will be set to the zero and full scale points. If you then move th sliders manually, the control will read custom to indicate that it is some setting other than the available automatic settings.

Kiril

Kiril,

Thanks for your further reply and sorry to belabour the point, but I expect that I may be responsible for some confusion due to my poor initial description. As I understood the experts, they were suggesting the 9 - 248 were set in the preferences for the black and white point tools, so when actually using these tools, the blackest point in the image is actually set at 9 and the whitest point is actually at 248, rather than 0 and 255 respectively. This has the effect of a less than full dynamic range to the image so when printed, the images brightest areas would have some texture from ink laid down and would not be just paper white. And the blacks would, of course, be likewise in the dark end. If I am incorrect, everything I thought was so, just got tossed out the window. If I am correct, I was merely asking if there was a way in PWP preferences to set the Full Range 0% and 100% to 9 and 249 (or 4% and 96% I guess) so it would mimic that method when the Full Range button was pressed, rather than manually setting the sliders to these two points.

And thanks, I now understand the Custom part of the Dynamic Range slider.

I have some further questions about the RAW dialogue, but will leave those for another day.

Marv

Full range sets the black and white points of the image to 0 and full scale, respectively. If you want to back off these values, you need to do it manually.

Kiril

Perhaps I'm missing something, but can't this be automated using curves? Set (approximate) the end points for a linear curve; save the curve; open the curve in a text editor and edit the approximate settings to 9 and 248; and save.
That curve is then available for use in a workflow.

Something to keep in mind when setting black/white points or expansion to Full Range is the color space model in which it is done... and also if the black/white points require color cast removals... ...as images and one's preferences for them are not always the same each time for every image...

PWP's strength is the availability to gain access to image data and manipulate it to preferences... ...but also is its weakness for new users and non-adepts of the program...

Most non-PWP Raw Converters use the RGB color space model for conversion and edits [setting black/white points or expansion to FullRange... among other editing features].

PWP's RAW Dialog has a default HSV color space model or an optional HSL color space model for edits [setting black/white points or expansion to FullRange... among other editing features] after a RGB conversion and RGB gamma expansion.

Following are illustrations for the FullRange expansions [no other edits] of the same CR2 raw file after a RGB conversion/2.2 gamma expansion in various color space models... and black/white point color balance... ...they are not the same... ...as they are all technically correct, perhaps one's preferences and artistic sense should now make the choice for a base image for further editing!!!! ...[perhaps to increase the shadow/lower mid-tones brightness/colors]...

Kiril,

Thanks for the update.

Bob,

My recent explorations have been into PWPs RAW dialogue and, unless I am missing it, there does not appear to be a curves capability. The Grey and Colour tabs each have a histogram but no curves function. I understand that I could do the type of curve, that you suggest, in the general PWP editing workflow. Up until recently, my usual workflow has been to RAW convert my images in NX2, then bring into PWP where, for many images, I would apply the Full Range under the Levels and Colour transform (among other things). As this became somewhat tedious, I decided to investigate the capability of PWPs RAW conversion process and whilst doing so, came upon the Full Range slider and associated drop down boxes. That got me to wondering if I could shortcut things and do the 9 - 249 thing at this stage with a single-click custom set up. I have Photoshop and NX2 set up so the black and white points are 9 - 249 rather than 0 - 255.

Den,

Thanks for the added information. Although I have been using PWP for quite a few years, my knowledge is not deep enough to fully grasp the "under the hood" technical stuff. I guess I would be considered a "non-adept" as opposed to a "new user"! Having said that, I find PWP to be one of the most user friendly of all the image editing programs. Your points about the different colour space models are interesting and causes me to conduct some experiments to determine which one is most suitable for which style image. So many choices!! Perhaps it would be better if only vanilla was available......

Marv

Marv...

I was feeling a bit uncharitable this morning. By the time I had something to eat... the editing time period had closed!

In truth, my illustrations for the HSV and HSL RAW Dialog 'FullRange' expansion are self-serving in that they DID NOT include Color tab edits... had they been made, their overall appearance would be closer to the RGB BrightnessCurve illustration. This is because changes in color [hue/saturation] will occur in the RGB color space model at the same time as changes in luminance are made...
...so when one is trying to simulate settings from other editors with PWP in its default HSV or option HSL color space mode, V or L settings will at the very least require corresponding S and sometimes H changes in order for the resulting image version to appear similar to one that only has RGB color space model edits... [Hint: nothing says you cannot change the Gray tab gamma expansion setting from its 'RAW File Settings' default when making either HSV or HSL RAW Dialog edits]
...still there will be nuiances and some images will preference better [and perhaps more easily] with RGB color space model edits...

...more food for thought! ...more options!! ...most of all -- HAVE FUN experimenting!!!