27.9 Read pixel values of images

The outputs are suppressed using eval = F because of issues with ImageMagick and GitHub Actions.

Code

library(magick)
image = image_read("https://www.r-project.org/logo/Rlogo.png")
is(image)
print(image)
plot(image)

Code

library(reshape2)

df = image[[1]] %>%
  as.integer() %>%
  melt()

colnames(df) = c('x', 'y', 'rgba', 'value')

df = df %>%
  mutate(rgba = case_when(rgba == 1 ~ 'red',
                          rgba == 2 ~ 'green',
                          rgba == 3 ~ 'blue',
                          rgba == 4 ~ 'alpha',
                          TRUE ~ ''),
         rgba = factor(rgba, levels = c('red',
                                        'green',
                                        'blue',
                                        'alpha')))

Code

## Take a random sample so it plots faster
dg = df[sample(1:nrow(df), 100000),]

g = ggplot(dg,
       aes(x = value,
           fill = rgba))+
  geom_histogram(color = pubbackgray,
                 binwidth = 16) +
  facet_wrap(~rgba) +
  scale_fill_manual(values = c('red',
                               'green',
                               'blue' ,
                               'gray')) +
  labs(title = 'Distribution of Red, Green, Blue, and Transparency') +
  guides(fill = guide_legend(nrow = 2))



g %>%
  pub(type  = 'hist',
      xlim  = c(0, 255),
      #ylim  = c(0, 15000),
      facet = T)