Understanding Success Criterion 1.4.3: Contrast (Minimum) and NOTE Clarification

[PICARDBRB]

Ref: NOTE in the criteria on Image Editing application and measurement.

Is the NOTE section referring to video editing applications? Or just still image editing applications like photoshop? For text added to videos in post-production, such as name keys, legal lines, bullet points, etc. , what is the size of text to have it considered “large” from the point of view of WCAG given differences between video editing and image editing applications?

Context: Video editing applications do not have any explicit pixel densities. In the video world you really only talk about PPI for displays (phones, monitors, tvs). A video clip has no ppi characteristic, unlike a still image. That said, when you export a still image from a video and open that image in photoshop and check the ppi in photoshop, it will say 72 ppi. Perhaps that’s what is intented for 72 ppi applications but this is not clear? If it does apply, then to have large text, we would use at least 24pt or 19pt bold, rather than at least 18 point or 14 point bold for video editing applications.

NOTE from Success Criterion: Because different image editing applications default to different pixel densities (e.g. 72 PPI or 96 PPI), specifying point sizes for fonts from within an image editing application can be unreliable when it comes to presenting text at a specific size. When creating images of large-scale text, authors should ensure that the text in the resulting image is roughly equivalent to 1.2 and 1.5 em or to 120% or 150% of the default size for body text. For example, for a 72 PPI image, an author would need to use approximately 19 pt and 24 pt font sizes in order to successfully present images of large-scale text to a user.”

Thanks for your help.

[PICARDBRB]

Hi all, wondering if you had an update to this question for clarification on the NOTE in the success criteria at the top of this issue? thanks for your help.

[Myndex]

The meta data inside an image indicating a specific ppi is essentially meaningless in that it has no effect on the image resolution. A 320x240 image that has 72ppi set is identical in resolution to a 320x240 image that has 120ppi set.

The size that image is displayed is controlled either in the HTML tag, or in CSS, and those settings (by which I means width or height) ignore any "dpi" setting in the image's meta data.

The CSS reference px is tied to the canvas abstraction layer, and is defined as 1.278 arc minutes of visual angle, which is a 96ppi screen when viewed at 28". When editing images intended for the web, a best practice is to set the image editor's units to px.

For WCAG 2 contrast, Large text is 24px normal or 18.7px bold (pt * 1.333 = px).