lens – How to determine a diffraction-limited MTF at a given contrast?

Tables and formulas for determining the "extinction" / "zero contrast" modulation factor in lp / mm at a given aperture for a diffraction limited system are well known.

How to determine the theoretical maximum MTF, at a given opening, which will produce a non-zero given contrast (eg 50%, 10%, 20%, 90%)?

Objects in a 3D space: color contrast on background

Is there a tool to help me choose the appropriate colors for:

  1. Objects
  2. Context

in the 3D space. The colors must have a good contrast.


Here is an example of my options for background color:

Color of the background: #c8c8c8c , color of the object: #576675

background color = # c8c8c8

Color of the background: #888888 , color of the object: #576675

background color = # 888888

Color of the background: #444444 , color of the object #576675

background color: # 444444

automatically calculate the contrast

A user can change the default design of their site by selecting a color. This color is applied to the color of the menu background. The problem is that I have to change the color of the menu text according to the selected color (for example, if the user chooses dark green, the color of the text should be white).

I only want to use white or black as the text color for the menu and know how to calculate if white or black allows better readability.


The website is for sports teams. As teams often have specific colors, I want to give them the opportunity to add team colors to the site. the models will not work because I can not provide all the colors with the models. I've also chosen not to give them the ability to set the color of the text because I think it's a physics problem (contrast)

Readability and contrast for light weight sources. With regard to accessibility

I develop a web application, from an approved design, I have the task to evaluate if it is readable.

The question is: the body of light, modifies the consideration on the contrast? because it's clearly less legible.

Thank you for the time.

color palette – The clearest "gray" shade of gray to contrast with white

I often use a slight shade of gray such as rgb (242,242,242) in my designs to create a subtle contrast with the white, eg. for the background of lines alternately in a table.

I can easily distinguish between this gray and white on my screen (a 27 "4K), but on other screens, this is not always the case, which affects my designs and could affect the user experience.

Reasons may include poorly calibrated / poor quality screens.

Assuming all accessibility standards have been met, is there a "lighter" shade of gray that:

  • Provides a contrast with a white background
  • No significant impact on the readability of the text in the dark foreground
  • Will be displayed reliably for most users under normal conditions

bit depth – theoretical contrast of the 8-bit monitor

Imagine a perfect monitor that can display pure blacks and perfectly calibrated.

What would be the contrast between its second darkest shade of black, 1.11 for the blue-green-red subpixel and the brightest white with 256 256 256 values ​​for RGB?

Please note that I mean the second darkest shade of black, which means that the pixel is active and the light emanates even very weakly. In particular, I do not want people to confuse this with the darkest shade of black (0.010 rgb), which means that the pixels are completely disabled and that no light is leaving them.

This is due to screens with perfect black, regardless of the maximum brightness value, the contrast is always infinite. That's why I ask the question about the second darkest black, and not about total black.

I know that SDR monitors have a gamma curve target of 2.2 and 256 possible values ​​because they are 8 bits. I know that 8 bits have a contrast ratio of 256-1 assuming that the brightness change is the same between all the bit values, but since the encoding of the 8-bit digital format is not linear like RAW files, I do not know at all which contrast / dynamic range 8 bits supposed to be becose, I do not know how much the individual values ​​of the bits are spaced.

If the maximum brightness of this theoretical 8-bit SDR monitor was 100 cd / m2, which brightness would be the second shade of darkest black?

Contrast vs sharpening? – Stack Exchange Photography

Sharpness and contrast enhancement are related. The difference is that although contrast enhancement is a global (That is, it applies to the entire image, although it can of course also be limited to areas of interest), sharpness is an important element. local operation that affects boundaries and edges.

Sharpness increases the contrast during sharp brightness transitions, ie. edges, to make them stand out more, which is perceived as an increased sharpness. The parameters to choose are the range of edges to be affected (how big the difference must be), the magnitude of the increase / decrease in tonal values ​​to be applied and the radius of reduction of this effect.

The contrast is increased by applying an S-curve to the chart, i.e. the luminous values ​​will become even clearer and the dark values ​​even darker.

There is even a kind of twitter using sharpness to obtain an improvement of the local contrast: the fuzzy masking with a low value but a large radius (generally hundreds of pixels) produces an effect of "sharpness" interesting.

print – Do I need to buy filters to control contrast in multi-grade papers?

Short answer: No, you do not need to buy filters.

Long answer: Unless you already have a dichroic head with built-in filters, you may want to buy the Ilford filter group anyway if you want to use contrast control. [Multigrade paper is usable without filters. Filters simply give you more control / choice from the same paper stock.]

Using color control lights is a bit difficult, but you can do it if you are ready to solve some of its problems.

First hurdle: Set values ​​on the LED that match the filters. You can somehow give an idea of ​​the guest and approximate results, but the results are rather sloppy. I have not read anything yet from a photographer who has managed to get a complete 1: 1 mapping for all filter categories.

In addition, you may encounter problems with accuracy between bulbs if it is time to replace them, if updates are made to the control software, or even as the LEDs and their controllers change. diet are getting older.

Second hurdle: The exposure time and rigging to the system of your enlarger. You will want either a shutter-controlled exposure timer or be very careful with your selection.

The power-on response time of some light bulbs may vary to reach the set color temperature, while others simply turn on with a default white light setting each time the power is turned on and wait that orders change. [For example, the last time I'd heard it, Philips Hues went blank when the power was applied.]

This will make use more difficult with most power-based exposure timing systems, which turn on and off the bulb for exposure.

The filters will last for years if treated carefully, and remain reliable and consistent while providing even control steps.

In summary, if you mainly want to print, buy the filters. If you want to tinker and experiment while making prints, explore and play to see what you can do.

Web Design – Why is color contrast important and the example of online businesses that are currently using it?

Someone can give me some examples of color contrast for accessibility What websites do big companies use?

I only find 2 examples of live websites



I make rocker contrast switches for my ecommerce website, but I have not found any other ecommerce website that does.

Can any one give me a reference to that color contrast that other websites use?

I want a reference for sites that actually use this feature

Why does an increase in Y-chain contrast cause apparent desaturation?

And is this the same phenomenon we see when colors appear less saturated in the middle of the day compared to dawn and dusk (when the contrast of brightness is reduced)?